GEM RP90 successful repair

Posted by: Kumi_27

GEM RP90 successful repair - 02/05/13 07:07 AM

Hello all

This is my first post here, so I'll introduce myself.
I'm Michael, from Poland, Europe, turned 44 this year... adult beginner, I think smile
Somehow I always wanted a piano to learn & play but never got to buy one, actually.

But some weeks ago I was browsing online local ads and found a "digital piano" for 50$.
At first I thought that it must be only some cheap keyboard but it turned out to be a full size GEM RP90, big, black and broken. Battery leak.
As I learned later, it was a common failure in Generalmusic products - leaked battery caused failure of CPU board.
I bought it almost for fun, a big paperweight.
Maybe to salvage the keybed in some hobby project.
But I thought "I have to dust off my electronics knowledge and check this board first"...

Power on caused only a row of grey bars on the LCD and lit a set of 8 LEDs.
Like the CPU hanged in the middle of startup.
I examined the board - some traces around the battery were slightly eaten by the electrolyte, also some connections between traces and SMD IC pins.
Removed the battery (it looked new, apparently someone already tried to repair the piano).
In meantime learned to solder and unsolder SMD elements using some unconventional homemade tools smile

Turns out, the RP90's mainboard (and probably other RP's by GEM, and some GEM-made Baldwin Pianovelle too) is powered by Hitachi H8/3003 micro-controller with a Flash EEPROM and 2 static RAM chips. The sound is generated by the GEM proprietary DSP chip with wave ROM and DAC chip.
The PCB has place probably for second DSP (bigger polyphony models?) and additional wave memory.
And to my surprise, the keybed has it's own uC communicating over some sort of serial connection (maybe something like MIDI, but inside the instrument).
Keybed, as expected, from Fatar.
Maybe I'll post some pictures later.

The most damaged area was near the battery connectors - RAM and Flash IC connections.
I unsoldered the 3 ICs , checked and cleaned the board. One trace was broken and needed repair.
Flash was intact, with all the program inside. There's hope.
Soldered everything back - still doesn't work.
Then I thought, maybe the RAM was short-circuited by the battery leak...
I ordered two new RAM chips (~4$ total), yesterday night replaced them, today put the board back inside the piano and switched it on.

When the GEM lighted up the LCD and displayed * REALPIANO * RP90 I was very happy smile

Checked the keys, played the demos, everything works now.
Probably I'll put a coin lithium battery for RAM data retention.
Now I have to clean my GEM and make some minor mechanical repairs.

And to learn piano, at last. I hope smile


PS. English is not my mother tongue, so forgive me any errors.
Posted by: Paolo70

Re: GEM RP90 successful repair - 02/05/13 07:52 AM

Hi Michael,

My congratulations and best wishes for your new piano experience, and also my respect for such a corageous electronic engineering feat.

Now it's time to have some fun laugh

Ciao,
Paolo
Posted by: spanishbuddha

Re: GEM RP90 successful repair - 02/05/13 07:55 AM

Nice story. We also love to see nekid pictures.
Posted by: Kawai James

Re: GEM RP90 successful repair - 02/05/13 09:42 AM

Congrats!

James
x
Posted by: toddy

Re: GEM RP90 successful repair - 02/05/13 10:11 AM

That's the way to do it.... Very well done!
Posted by: Kumi_27

Re: GEM RP90 successful repair - 02/05/13 05:53 PM



Here's photo of the CPU board during the repair.
Top right corner is the area damaged by the battery leak.
Battery is already removed, and the two nearest ICs (flash and one of the RAM chips) unsoldered from the board. Traces to flash were the most corroded, but the IC survived.
RAM, on the other hand, was damaged.

Left side - sound generator (RAM, DAC, GEM DSP), mid-top - wave memory.
Right side - CPU, memory, logic gates and data buffers.
And some sort of service connector - data and address bus going to memory ICs.
Bottom - connectors to the other internal equipment.
From left - audio, power, pedal board, front panel, keybed (serial), MIDI.

Thank You for the comments.
More photos later smile
Posted by: Kawai James

Re: GEM RP90 successful repair - 02/05/13 06:19 PM

Truly impressive stuff!

Congrats again on the repair!

James
x
Posted by: xorbe

Re: GEM RP90 successful repair - 02/05/13 06:20 PM

+5 for any DIY fixes!
Posted by: Hubert

Re: GEM RP90 successful repair - 02/05/13 08:15 PM

woooo... not an easy task but you made it!!!
Posted by: Kumi_27

Re: GEM RP90 successful repair - 02/18/13 08:16 AM

Hi. Thanks again smile
I was on vacation, so the reply is a little late.
As promised, some photos of the inside.

The IC's soldered back in place - original flash ROM with repaired traces, and two new RAM chips on the left.
Battery so far not needed, maybe I'll add it later.




Cover removed - You can see the two speaker's cabinets and the electronic boards in the middle
Green "digital" main board on the left, main "analog" board in the middle (power supply, power amplifier) and the audio/MIDI in/out board on the back side of the piano.
The wide ribbon cable is for the front panel (main LCD, buttons and LEDs).
The keybed controller is under the keybed on the left side and is not visible here.








Fatar keybed TP 20/21

Posted by: Qbert

Re: GEM RP90 successful repair - 02/18/13 02:54 PM

Nice work, weldone!

Originally Posted By: Kumi_27
In meantime learned to solder and unsolder SMD elements using some unconventional homemade tools smile

I'd be curios to see the tool!

Originally Posted By: Kumi_27
And to my surprise, the keybed has it's own uC communicating over some sort of serial connection.

Some kind of multiplexing IC?
Posted by: Kumi_27

Re: GEM RP90 successful repair - 02/19/13 02:35 AM

Originally Posted By: Qbert
I'd be curios to see the tool!

Well, for soldering I used some common low voltage soldering iron with adjustable power, nothing special. Only had to file the tip.
But for the desoldering...
This is the main part of the ultimate SMD IC desoldering station - 75W GU10 halogen lamp grin



Plus the socket & cable, pair of tweezers and DIY stand from an insulated bent wire to place the lamp ~10-15mm above the PCB.
I used a liquid flux, too. And, of course, sunglasses grin
Got the idea from http://www.youtube.com/watch?v=HkO71G4wvo4
But You don't really need the temperature sensor.
I just used the flux, switched on the lamp, watched the IC and tried to pick it with tweezers.
Depending of the IC size and thickness, after 45s~1m20s the chip was up, nice and clean.


Originally Posted By: Qbert
Some kind of multiplexing IC?

No, there are too little wires, must be another CPU. I traced most IO pins of the Hitachi H8 on the board.
Multiplexing is used for the front panel, ~16 IO pins are connected there via the wide ribbon cable.
But the H8 has two serial ports.
One pair of Tx/Rx pins is used for MIDI communication, and the other pair is going to the keybed controller so there must be another CPU capable of serial communication, scanning the key contacts and calculating the velocity.
The connector has only 6 pins, one is ground, two for Tx/Rx signals, one logical pin (maybe enable signal or something) and remaining two are shorted by the 10R resistor.
I will probably disassemble the piano for cleaning so then I'll check the keybed.
Posted by: Nigeth

Re: GEM RP90 successful repair - 02/19/13 04:57 AM

I'd guess that the CPU is connected via either a SPI or I2C serial connection to the main controller. It's simple, offers enough bandwidth to transfer all of the key and velocity info on time and there is hardware support in nearly every microcontroller
Posted by: Jake Jackson

Re: GEM RP90 successful repair - 02/19/13 12:15 PM

Interesting coincidence. Two weeks ago, I bought a GEM RealPiano2, used of course. It plays, but the led has dead pixels. Your keyboard looks similar. Was it fairly simple to open yours and have the view that you show in your first picture?

(I've been hesitated over opening mine to see if the repair might be simple. The last keyboard I opened, an Ensoniq, had several layers of small boards and connections above the main board, and each had to be removed just to fully expose the main board. Had to remove about 20 screws, some hard to find and reach. Great sounds in the Ensoniq, but complicated to work on.)
Posted by: Kumi_27

Re: GEM RP90 successful repair - 02/19/13 12:45 PM

Originally Posted By: Nigeth
I'd guess that the CPU is connected via either a SPI or I2C serial connection to the main controller.

This H8/3003 CPU has no integrated SPI nor I2C, only 2 serial ports with sync/async mode.
SPI should use 4 wires - here's only 3. For I2C the pull-up resistors are not here.
Really, to me this looks just like MIDI but using TTL levels instead of current signal. Maybe it's faster, too.
But without logic analyzer I can't tell for sure.

Originally Posted By: Jake Jackson
Was it fairly simple to open yours and have the view that you show in your first picture?

Congrats for Your GEM smile
Opening of this one is really simple. The top cover has only 4 screws on the back and then You have to slide it a bit forward to release two "locks" on both sides (just 2 another screws, which are going into some keyhole shaped cuts) and some others on the back.
Then the cover can be lifted up and that's all.
I removed also the sliding keyboard lid - just unscrewed another two screws (they limit the lid movement).
Front panel is still in place but it's just another set of few screws.

But if the LCD has dead pixels then I'm afraid the only way is to replace the display.
This is probably some generic 2x16 LCD display with integrated controller, You just have to find a compatible model.
Posted by: dewster

Re: GEM RP90 successful repair - 02/19/13 05:22 PM

Fascinating Michael! Thanks for sharing! Awesome desoldering hint.

Added this thread to the nekid pichures collection.
Posted by: Jake Jackson

Re: GEM RP90 successful repair - 02/23/13 10:34 AM

Originally Posted By: Kumi_27
Originally Posted By: Nigeth
I'd guess that the CPU is connected via either a SPI or I2C serial connection to the main controller.

This H8/3003 CPU has no integrated SPI nor I2C, only 2 serial ports with sync/async mode.
SPI should use 4 wires - here's only 3. For I2C the pull-up resistors are not here.
Really, to me this looks just like MIDI but using TTL levels instead of current signal. Maybe it's faster, too.
But without logic analyzer I can't tell for sure.

Originally Posted By: Jake Jackson
Was it fairly simple to open yours and have the view that you show in your first picture?

Congrats for Your GEM smile
Opening of this one is really simple. The top cover has only 4 screws on the back and then You have to slide it a bit forward to release two "locks" on both sides (just 2 another screws, which are going into some keyhole shaped cuts) and some others on the back.
Then the cover can be lifted up and that's all.
I removed also the sliding keyboard lid - just unscrewed another two screws (they limit the lid movement).
Front panel is still in place but it's just another set of few screws.

But if the LCD has dead pixels then I'm afraid the only way is to replace the display.
This is probably some generic 2x16 LCD display with integrated controller, You just have to find a compatible model.



Thanks. I'm still working up my courage to dive into it. Mine appears to be a bit harder to get into, with all of the screws on the bottom and under the end-caps. I want to do a thorough inspection and cleaning, and see if I can repair two keys on the far right that were broken. My vague hope is that I can find a compatible lcd display on a visit to Radio Shack, but I dimly suspect that I may be spending more time looking at electronics catalogs than I can plan for right now. I'll post some pictures once I have it open. I'm interested in learning if our interiors are more or less the same, but with simply different code burned into the chips.

How is the sound of your GEM RP90? I'm finding the RP2 to be lively, and it has a slider that by default controls the velocity response. Very nice to have--I can play chords with one hand and move the slider with the other until the sound is right for specific pieces, which also makes it very good for controlling software pianos. Each note can be tuned separately, too, using the same slider. The one problem is that I have to watch out for long sustains. The modelled sounds are great on the attack and a fairly long decay, but once they eventually die, I hear what sounds like an old fashioned, very well-looped sample.

All in all, I'll echo the popular sentiment--I wish GEM had survived as a digital piano maker. I rarely hear of the organs they now sell in the US. A more specialized clientele, I imagine. More than once I've wanted to write them to ask that they re-enter the market or pair with Modartt to create the next step in the evolution.

You may be far ahead of me in searching for additional information. But just in case you are starting to do further research, are you familiar with the GEM threads on the Keyboard Player forum at http://forums.musicplayer.com/ubbthreads.php/forums/18/1/The_Keyboard_Corner ? David McMahan. who was once the head of US marketing and apparently support for GEM still writes there. You must register to search the site, and specify the range of years to search in, but the results may be of interest.

Finally, although the main GEM site is more or less dead, I've run across some subsites that they still keep open for downloading old manuals and some tech references:

http://www.generalmusic.us/Manuals/

And: http://www.generalmusic.us/GEMFiles/Upgrade/GemOS/Oldproducts/

However, there is disappointment lurking in that last site and the folders that can be reached by moving up in the directory structure. Most of the service manuals require a password. I wrote GEM to request one, but haven't heard back...

Looking forward to hearing more about your instrument and what you make of it when you have time.
Posted by: Kumi_27

Re: GEM RP90 successful repair - 02/25/13 09:26 AM

Originally Posted By: Jake Jackson
My vague hope is that I can find a compatible lcd display on a visit to Radio Shack, but I dimly suspect that I may be spending more time looking at electronics catalogs than I can plan for right now. I'll post some pictures once I have it open. I'm interested in learning if our interiors are more or less the same, but with simply different code burned into the chips.

I suspect, that GEM didn't used anything fancier and it will be some generic 2x16 display with Hitachi HD44780 compatible LCD controller. Lots of replacements are available. Even with different colours smile

Originally Posted By: Jake Jackson
How is the sound of your GEM RP90? I'm finding the RP2 to be lively, and it has a slider that by default controls the velocity response.

Well, don't have much to compare with but simply said, I like it.
Controls are somehow limited and slider is for volume only, but there are additional options for adjust the touch sensitivity (3 steps), brilliance, tuning, piano frame size etc. via buttons and menus.

Originally Posted By: Jake Jackson
You may be far ahead of me in searching for additional information. But just in case you are starting to do further research, are you familiar with the GEM threads on the Keyboard Player forum at http://forums.musicplayer.com/ubbthreads.php/forums/18/1/The_Keyboard_Corner ? [...]

Thank You very much for the links, they're new to me, as well as the most of the piano stuff, I started just as I bought my GEM.
I found the old manual folder before, but the other links are also very interesting.
For example, I found the self-test sequence and figured out the firmware number.
Maybe I can make a serial MIDI cable for my DP, there are some schematics in the service section.
However I don't think anyone would reply to the password request...

I found also some general informations in the Web Archive - http://web.archive.org/web/*/http://www.generalmusic.com/

Originally Posted By: Jake Jackson
Looking forward to hearing more about your instrument and what you make of it when you have time.

I have to clean it inside and repair the lid.
But for now my GEM is quite ok and I can play it. Now I just should learn to play... smile
Posted by: Jake Jackson

Re: GEM RP90 successful repair - 02/25/13 12:55 PM

Originally Posted By: Kumi_27
Maybe I can make a serial MIDI cable for my DP, there are some schematics in the service section.
However I don't think anyone would reply to the password request...


The best midi solution I've found with my GEM is my M-Audio Uno cable, which has midi in and out cables connected to a usb plug. No need for the MUMBO software or any configuration. The midi cables go into the keyboard, the usb cable goes into the computer, and it works instantly. (No need for an old-fashioned midi card in the computer or anything else.)

Thanks for the links. Looks as though there is more to learn...
Posted by: Kumi_27

Re: GEM RP90 successful repair - 02/25/13 01:56 PM

As for the LCD - better check the model in Your piano first.
Hitachi is very common but I'm not 100% sure GEM uses that.

Probably I'll buy some USB-MIDI cable.
But GEM has "To-Host" interface, which is basically a RS-232 (serial) connection, found also in instruments from other manufacturers (like Yamaha).
You install the serial MIDI driver, connects only one cable and it works as well smile
Posted by: Mooncalf2012

Re: GEM RP90 successful repair - 12/06/13 06:16 PM

The password is 2571 (also 5069 for some).
Posted by: Mooncalf2012

Re: GEM RP90 successful repair - 12/06/13 06:33 PM

The NiCd can be replaced with a Varta 3.6V 80 mAh NiMh (green, rechargeable) or equivalent. A lithium battery may work if it is 3.6V and rechargeable, but the NiMh is the same form factor, and no mods necessary, just solder it in and go.
Posted by: Kumi_27

Re: GEM RP90 successful repair - 10/24/14 02:43 AM

Small update - for all of You who will read this thread in the future hoping for repairing Your GEM RP90 (and similar).

Including mine, I have now two confirmed cases of repair.
In both cases, cleaning/repairing the board and replacing the static RAM chips solved the problem.
Battery can be either replaced by a NiMH one or just removed if You don't care about on-board note recorder. The piano is working fine without it.
The RAM ICs supply voltage is separated from the rest of the board by a transistor because of the backup power. Maybe this is the reason that only the RAM is damaged by the leaking battery.

According to schematics, the two RAM ICs to replace should be HM628128 - Hitachi CMOS static RAM 128k-word x 8-bit (1Mbit). SOP-32 (32-SOP-525) form factor. CPU is afaik 16MHz so access time should be probably 55ns.
For battery data retention You should use low power versions.

On my board actually there were two Samsung KM681000CLG-5L chips.
I couldn't buy them so I used Lyontek LY62W1024SL-55LLI and they're working as well.
Any memory with the same specs will do.

Flash ROM should be ok.
The type is AM29F800BB-90EC - AMD 8 Mb (1M x 8-Bit / 512K x 16-Bit) TSOP-48 CMOS 5V flash memory with bottom boot sector. The firmware should be still available somewhere on the GEM USA support pages.


Posted by: Jake Jackson

Re: GEM RP90 successful repair - 10/24/14 01:12 PM

Many thanks for this update. I do not need to make these repairs, but maintaining an ongoing catalog of repairs that work is extremely valuable. We can keep these great instruments working!

(I still haven't replaced my display. I plan to try later this year, and I will post the results.)
Posted by: DoItYourselfGuy

Re: GEM RP90 successful repair - 11/30/14 04:59 PM

Hello - I have a Baldwin RP100 with the same battery leaking issue and have determined my RAM chips need to be replaced.

I can't find the lyontek or the Samsung chips you mentioned for sale in the USA. I am amateur at these types of repairs and I did my best to search the internet and found this chip - SRAM Chip Asynchronous Single 5 Volt 1m-Bit 128k X 8 70ns 32 Pin Molded SOIC

link to the chips webpage at Jameco electronics USA:

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_391831_-1

My question...can you help me determine if this chip is compatible and will work in this piano's cpu? As far as I can tell the specs match up except for the 70ns instead of the 55ns. I don't know if that speed difference will cause performance issues or not, or if there is another difference I haven't discovered. I found other chips that met the specs but the physical dimensions were not 11mm x 20 mm which is the size of the Samsung chips on the CPU.

If anyone could tell me if this chip would work I would be very appreciative. If it won't work maybe you could suggest a company in the USA who sells the correct chip. I prefer not be buy overseas because I assume shipping costs would be high.

I've taught myself to solder and have the supplies needed to make install the chip and I would like to bring the piano back to life if anyone could help with their advice.

Thank you for your time.
Posted by: Kumi_27

Re: GEM RP90 successful repair - 12/10/14 06:25 AM

Imho 70ns will be too slow for the CPU clock speed and may cause problems.
1/(16MHz) gives 62.5ns - therefore 55ns memory should be used.
Low power CMOS, 5V, 128K x 8.

You can use mentioned Lyontek, Samsung, Hitachi.
Samsung K6X1008C2D-GF55 (or -GB55) should work too (they are on ebay), or Alliance Memory AS6C1008-55SIN - there are many types of compatible chips.

PS. In the past I bought some IC's on ebay across the ocean so it's really not a big deal smile
Posted by: Dwscamel

Re: GEM RP90 successful repair - 12/10/14 08:54 PM

Wow, Michael, wow!

If you put half as much energy into learning the piano as you must have with electrical engineering, I think you'll get plenty of great moments out of it smile.

It must feel awesome to have such a close connection with your instrument. After all, most pianists don't even know how their pianos work :$.
Posted by: MacMacMac

Re: GEM RP90 successful repair - 12/10/14 10:10 PM

Not so. RAM speed need not match CPU clock speed.
Originally Posted By: Kumi_27
Imho 70ns will be too slow for the CPU clock speed and may cause problems.
1/(16MHz) gives 62.5ns - therefore 55ns memory should be used.
Low power CMOS, 5V, 128K x 8.
Most CPUs devote several clock cycles to a RAM access cycle.

Consider a fast PC running a CPU with a 3 GHz clock. Your method of computation would require RAM speed of 0.333 nsec. There's no such thing!
Posted by: Kumi_27

Re: GEM RP90 successful repair - 12/11/14 03:31 AM

Your "most CPUs" is right - but not "all CPUs".
Modern PC (or better to say modern PC's CPU) has a special memory controller just because there's no such thing as 0.33 ns memory. Yet. The rising speeds of memory chips are going to reduce the waitstates to minimum. To achieve one clock cycle access.
But You still have to match the memory access time with the memory bus speed. All the numbers on DRAM sticks indicate the access time, the waitstates and such, it's also programmed in the SPD chip. The controller can accomodate to that.

And here we have something "oldschool" - not modern "the most".
I'd say - back in the day it was "the most" but now we have 1GHz quad-core phones wink

Inside GEM's board is a 16MHz microcontroller, most probably running the direct memory bus with zero waitstates.
The factory chips with 55ns, which is less than CPU cycle time, suggest just that.
Also - async static RAM is fast enough and is often used just for that purposes - small and fast embedded systems, and it does not need the extra controller needed for memory refresh in dynamic RAM.
I know such designs, I programmed similar ones years ago at university (it'll be >20 years already).

Maybe the 70ns will work - but maybe not.
H8/3003 can work with or without waitstates, with different memory configurations, it's programmable and versatile CPU.
I don't know how the firmware is written and if the hardware won't go off-time.
But why bother? The price difference is negligible and I think it's better to have a direct replacement with 55ns.

I could joke "Trust me, I'm an engineer" but I really have the MSc in that field smile
Know a bit about sound synthesis too.
Unfortunately, in playing the piano I'm not that good... still a way to go...
Posted by: Ed NL

Re: GEM RP90 successful repair - 03/01/15 08:06 PM

Hi,

This is my first post. My name is Ed, I'm from the Netherlands.
I've played piano as a kid until I was 18 years old. At that point, I didn't like the weekly piano lessons. Also, the piano I played on was a bit irritating with stuck keys, being out of tune and other problems. So, I stopped playing. But a few years later, like my teacher had predicted, I wanted to play again.

This time, I bought a digital piano, a General Music Realpiano 2. I was able to buy it 2nd hand in very good condition for 600 euros if I remember correctly. It was 2004 or 2005 I think.

About two years ago it started to give problems. While playing, the sounds would distort.
Luckily I mostly used it with Steinberg the Grand II VST, which is a wonderful VST by the way.

The problems got worse, but the MIDI-Out still worked, so with volume at zero I could still enjoy it.
Over time I heard about the battery-leak problem, so I decided to open up the piano and check the mainboard.
And, yes, the battery had leaked. So I removed the battery and cleaned up the print a bit.
And then, it stopped working altogether.. No more MIDI-out. No more sound. No LCD display. Oops.

Attached, please find a photo of the mainboard and one of the damaged area.
The damage is definitely in circuit around the SEC/Samung memory chips. Actually, these seem to be waveform ROM chips. That explains the scrambled sounds. Those would be a lot more difficult to replace, as I don't have the ROM contents.
But also a few pins of the EPROM might have been damaged, but the EPROM might have survived.

So, I will probably have to replace the ROM memory chips.
Kudoos for Micheal by the way! Great work and very nice of you to document it all so well. Thanks!

Even if I would be able to source the ROM chips, with the waveforms in it already, doing SMD soldering myself is a bit too much for me (normal soldering I do, but SMD is a step too far).

So, I thought of an alternative, as I mostly use the piano for connecting it to the Steinberg The Grand VST.
I was wondering if it would be possible to use the signal coming from the keybed and then wire it straight to the MIDI-Out port.
Perhaps it might need some signal adjustments (resistor?), and I have to be lucky that the serial signal coming from the keybed is indeed MIDI and not some other serial protocol.
If it's not MIDI coming from the keybed, then I could use an Arduino microcontroller to convert the keybed signal into midi and then connect it to the midi-out.

**EDIT**
It seems the signals from the pedals and the keybed are combined and then sent to the microprocessor. See last photo, which I got from the service manual page 7. The keybed calbe has these pins:
1. RX
2. NEXT
3. GET
4. RST
5. TX
6. GND

Michael, you seem to know a lot about this.. Perhaps you can give me some pointers?
Am I correct that the cable from the keybed, is the grey/blue cable coming from the right (directions like on the photo), and which connects to the mainboard on the bottom left, with a red connector?
Another similar cable runs, also from the bottom-left part of the mainboard to the board which is mounted above the LCD screen and all the buttons.
I reckon the cable on the top left of the mainboard has the Midi-signal, as it connects to the midi-panel on the back of the piano (north-west of the mainboard in the photo).
Another bigger cable, in the center on the top of the mainboard probably carries the analog sound output and connects to the amplifier/power board north of the mainboard in the photo).

I have also added an annotated photo. The wiring diagram is from the service manual which I got from http://www.generalmusic.us/GEMFiles/Service/ with password 2571 .








Posted by: Kumi_27

Re: GEM RP90 successful repair - 03/02/15 04:16 AM

Hi Ed.

I looked into this service manual and schematics and here I have some thoughts about it.
The main board has a H8/3003 microcontroller ("server"), the 2 other boards have H8/329 uC each, lets call it "clients".
The internal communication is done via some serial protocol. It might be MIDI on the TTL level (0-5V, not current loop), but not necessarily - the same protocol is used here for the local control buttons, LEDs and LCD display. I'm not sure if GEM used MIDI control messages for that. Probably not, and using 115 Kbps from RS232 standard (for example) will be faster than 31 Kbps from MIDI.

Both clients are connected to the same serial port of the server CPU (TXD1/RXD1)
Both connectors on the keybed/control panel side have the same pinout (below they're not in order)
1. TXD - transmit data. This pin sends the data to the main CPU board (where the pin is labeled RX)
5. RXD - receive data. This pin receives data from the main CPU board (where the pin is labeled TX)
4. ~RES/~RSTV/~RST - different description, but common function - negative reset. This is connected to the standard RC circuit for power-on-reset.
Might be also forced from the main CPU, don't know, the signal is connected to pin 113 of H8/3003, but the ~RES pin of it is on pin 71 with separate reset circuit.
6. GND/NC, from the main CPU side also connected to GND.

There are also 2 pins, labeled GET (3) and NEXT (2) - and they're looped and crossed on the mainboard between CN3 and CN4 connectors.
To me it seems like some token network - one client is programmed after reset to set the "NEXT" signal, then the second (via the loop) gets GET signal - the permission to transmit data to the server. Probably so, looking at the names smile
After transmission, it sets the NEXT signal, so the first client gets GET signal and switches off the NEXT. Atter transmitting data, it switches the NEXT signal on, giving the permission to the other client and so on.

Actually, I was wondering why on my GEM there's a loop between two pins on the keybed connector, only via 10 ohm resitor.
Now it becomes clear, my GEM has buttons and LCD connected directly to the main CPU and only the keybed uC is connected to the serial lines.
This way, the keybed uC always has GET signal when sets the NEXT one.

It may be possible to reverse-engineer this protocol.
Probably the GET signal should allow the client uC to transmit somehing (like key press on the keybed), but You must find the correct baudrate and figure out the data format.
There is also a receive in on both clients. I don't know, what kind of data the CPU might send to the keybed controller. Maybe only "loopback test" message during startup and nothing more and the keybed controller will work fine without it.
The GEM FAQ states, that for example You need to connect the pedals (and release them) before switching on the piano, because in other case they will work in reverse. It means, the pedals are checked during init/reset and then only transmitted when a position change is detected.
You can try and connect an Arduino board, and try to capture something on the RX pin. Later using SoftwareSerial library You can probably use both boards (keybed and control/pedal) with one Arduino. Or just connect the pedals directly to Arduino and write functions for it
(I made a MIDI triple pedal from a similar KORG unit and Arduino board)
I have a Saleae logic analyzer and some time ago I thought about checking the protocol inside my GEM, but just now I totally don't have a time for that, sorry... orz

***

As for the damaged board... I learned SMD soldering just to be able to repair my GEM.
Repairing such board is possible, but it requires patience and time - any service shop will charge You a lot for that, so I did it myself. Like I wrote, I practiced on some junk boards, like old DRAM sticks.
"SMD drag soldering" is quite simple to learn, and do not require any special and expensive tools.

The board is only two-sided, no hidden traces or layers, everything can be repaired.
Everything can be (and should be) checked with a multimeter/low voltage continuity tester.
You has the service manual and schematics - I did it even without that.
The distorted sound probably came from data or/and address lines shorted together and there is a high possibility, that the waveform and program memory is still good, just the board has breaks and shorts. And probably RAM to replace.
In my case, and in the second confirmed repair (user from Holland), the only really damaged thing was the static RAM.
In both cases careful board repair and RAM replacement solved the problem.
The static RAM is a CMOS chip and quite prone to damage.
On RP2 board they're also near the battery and use the same battery backup circuit like on RP90.
I think, if You spend a little time, You might be able to repair Your GEM too smile
Posted by: Ed NL

Re: GEM RP90 successful repair - 03/03/15 08:27 AM

Thanks a lot, Michael, for your extensive reply! I really appreciate your help!

I'll first try and interface with the keybed controller.
I'll try and hookup an Arduino to the TX/RX lines and see what I can discover.
The GET and NEXT line of the keybed interface, I can connect together with a 10 Ohm resistor, I assume.
With some luck, the keybed controller might send some data when I press keys. If I'm unlucky the controller will first wait for some special unknown code before it starts transmitting. I'm afraid using a logic analyser won't give results on my now defective mainboard.

I'll let you know the results.
If that doesn't work out, I'll try and learn the SMD soldering.

Ed
Posted by: sasabi

Re: GEM RP90 successful repair - 03/16/15 02:09 PM


Hello Michael and all
I Am Sandro and I'm from Italy.
Sorry for my poor English.

I read with admiration your repair of Generalmusic RP90.

I'm a teacher in italian school, music fan.
I have a Piano arranger Generalmusic PS1300 with a similar problem: loss of acid from the battery. The piano went to freeze.
After replacing the battery, the piano worked, but after a while disappeared the written on the screen and the lighting of the LEDs of the buttons on the control panel.
I state that my piano has the CPU board-motherboard separate from the and power amplifier board..
My attention was focused on the RAM. I noticed that the one that is on my motherboard (KM416C1204CJ-L6) is different from the original chip as shown in the schematic (HM5118160A LJ 16 Mbit DRAM, Ta = 70 ns). This suggests to me that has already been replaced once.
Both are now unavailable.
So, could you tell me a chip equivalent because I'm going to change the RAM (I know that may need just a reballing, but, like you said, these are very fragile RAM).
2) A last question, for your kind patience: the relay on the power board don't activate; I do not know if I even a power problem that comes from the final stage chips (TDA7294) or even if this is caused by the failure of RAM.
Confident in a reply illuminating

Thanks
Sincerely.
Sandro
Posted by: Kumi_27

Re: GEM RP90 successful repair - 03/16/15 05:02 PM

Hello.
Looks like I'm becoming sort of a guru of old GEM repairs smile

The dead battery probably caused the freeze of the CPU - the memory wasn't working because of low voltage.
Replacing the battery solved this problem, but in the meantime the acid probably destroyed some traces on the board and then the memory stopped working for the second (and last) time.

I don't think the memory was replaced.
GEM factory could use different ICs with the same function, coming from different manufacturers.
My GEM also had different chips than stated on schematics.
HM5118160A is a Hitachi 1Mx16 static DRAM with fast page mode. There are similar chips still available.
Current replacement are for exaple Integrated Silicon Solution ISSI IS41C16105C available from Mouser Italy http://www.mouser.it/Search/Refine.aspx?Keyword=IS41C16105C
or Siemens HYB 5118160BSJ (on ebay).
(I'm not sure about the package version used in GEM, SOJ-42 or TSOP-44/50, You must verify it by yourself)

The relay is connected to the "Muting" signal - it's connected to the CPU pin so I'm 99% sure, that it does not function because the CPU board is not working properly (hangs in the middle of startup sequence)
Again - the RAM should be unsoldered, then the board carefully cleaned of even small traces of battery acid, then any broken/shorted traces should be repaired. If the acid damaged bigger area (under other chips), You can unsolder them too and clean the board.
Maybe there are some chemicals to neutralise the NiCad acid, don't know.
I just used a fair amount of IPA, but I unsoldered both RAM chips and the flash memory, so I could clean and check the whole damaged area.
Then You can solder the new memory chip.
I hope You will be able to repair Your piano.
Good luck smile
Posted by: sasabi

Re: GEM RP90 successful repair - 03/19/15 04:40 PM

Hi Michael thank you very much for your precious wanted response, which gave me important tips.
Sorry for my late reply, but I'm Czech Republic for work.
I'll buy Ram chips on the web.
Thanks for equivalent model names of it.
I'll say you what's happening...
Thanks a lot..
sincerely..
Posted by: Jake Jackson

Re: GEM RP90 successful repair - 03/19/15 10:14 PM

A post on the Gearslutz forum links to an announcement that GeneralMusic is being restarted. I kid you not. Here's the link to the very brief GeneralMusic announcement:

http://www.generalmusic.com/

Here's the link to the thread on the Gearslutz forum:

http://forums.musicplayer.com/ubbthreads.php/topics/2652758/Generalmusic#Post2652758

Could be great news, yes?
Posted by: Kumi_27

Re: GEM RP90 successful repair - 03/20/15 02:23 AM

Some company from Finland bought the rights - it could be great, yes.
If only they're fans of the old GEM gear, not only want the logo.