Korg Forums

This request is addressed to all the "technicians" who have ever "put their hand" to their Korg M1 or similar (T1 / T3 Series).

Last week I turned my Korg M1 back on after more than a year. At the first start the screen presented a freezed boot text (I don't remember the content well but something like "Korg M1 version ...") with all keys completely locked for a few minutes. Off and ON again the keyboard, a completely blank screen (with backlight on) was presented but no text. [the rear contrast acts but no text appears anyway].

Of course, having a minimal electronic preparation, I opened it and proceeded to:

1) Change the backup battery 2032.

2) Check all the voltages coming out from the power supply board (PSU labeled KLM-1269) of +5V, +12V and -12V, are all perfect and stable (checked with an oscilloscope).

3) Carry out the recap (replacement of all electrolytic capacitors) of both the power supply board and the Mainboard (KLM-1266) with the same Faraday but with an increased voltage (e.g. 16V with 25V) and with a working temperature increased to 105 ° [although to tell the truth the measured values ​​of Capacity and ESR of the originals were not bad at all for the age].

4) Read and compared Bit at Bit the contents of the two EPROMs (IC23 and IC32) containing the Firmware v1.19 with the original dumps supplied by Korg, both found to be identical to the corresponding korg dumps.

5) With a thermal imager, I take pictures of the mainboard where the LS245 ICs and the IC6,7,8,9,10 are a little "turned on" (Temperature after a few minutes of 45/50 °)

Despite everything at boot the "Black / Empty Screen" persists

Request:
A) Advice? [apart from changing the mainboard (which cannot be found at "decent" prices)]
B) For those who have already tested it: the mainboard (KLM-1266) together with the power supply card (KLM-1269), [therefore without DAC card and buttons] is able to boot correctly [ok without sound emitted]? or is the DAC indispensable for the boot process?

Thanking you in advance for the patience of the "long read" I am waiting for some of your suggestions.
Thank you

Hi Crummy,

some years ago I had contact to a guy whose M1 didn't start - here's the outcome he had:

I thought you may be interested to hear my experiences with my faulty Korg M1 as we discussed a few months ago? You may remember I thought the main board was faulty and I ended up finding one on ebay for a reasonable price, from a fellow countryman of yours in fact.

On fitting the new board the exact same fault persisted, so I was very disappointed, but I noticed that if I unplugged and re-plugged in the LCD display whilst the synth was powered on it sometimes started to work. I thought the display might be faulty and was lucky enough to find a compatible one for just 8 Euros which, after a bit of soldering, I have just fitted, and now the M1 works perfectly. It's very strange that the display board could stop the whole system working; there were no short circuits on it and all the voltages were correct so I suppose it's just another strange fault to add to the knowledge base?

Maybe this could be of help...?

Regards,

Michael (aka the crimson thunder)

I thought you may be interested to hear my experiences with my faulty Korg M1 as we discussed a few months ago? You may remember I thought the main board was faulty and I ended up finding one on ebay for a reasonable price, from a fellow countryman of yours in fact.

On fitting the new board the exact same fault persisted, so I was very disappointed, but I noticed that if I unplugged and re-plugged in the LCD display whilst the synth was powered on it sometimes started to work. I thought the display might be faulty and was lucky enough to find a compatible one for just 8 Euros which, after a bit of soldering, I have just fitted, and now the M1 works perfectly. It's very strange that the display board could stop the whole system working; there were no short circuits on it and all the voltages were correct so I suppose it's just another strange fault to add to the knowledge base?

Hi Michael, and thanks for yor attention.

I forgot to mention that the M1 does not emit any sound or MIDI signals, also the function and numeric keys do not work and the related red LEDs are all off.


However, following your suggestion, I disconnected the Display with the keyboard ON and with the keyboard OFF. In both cases, no sound or MIDI signal is output.

(In the headphones, however, the typical "SHOCK" of the amplifiers is heard when M1 is switched ON or OFF)

Anyway thanks a lot!

From another user, whom I want to thank:

Before declaring the CPU dead, check with the oscilloscope that the clock and the reset signal are generated correctly. Looking at the diagrams we see that the clock is generated by IC3 (an LS74) and the reset comes out of IC4 which is a 3 pin M51951, similar to a transistor to look at. When a digital system does not start, after checking the correct operation of the power supply outputs, you must always check the clock and reset, because many times the problem lurks there. Without these two signals, the CPU and the rest of the logics do not start and the device remains frozen.

Thanks to this precious trace, I have studied a little better the MAIN BOARD (KLM-1266) wiring diagram from the Korg Service Manual and the SN74ALS74 and M51951 datasheets with relative pinouts, naturally coinciding with those shown in the Korg wiring diagram. (It is a pity that the Scan / "Analog" typography of the Service Manual, in some places, is really hard to read).

In the next few days, as soon as possible, I put the measurement set back up with the oscilloscope and check various signals. I have already verified, previously, that the oscillation was generated from the quartz which then allows the generation, of the signal CK and then CLK. (However, I did not measure if this was at 32MHz as per diagram).

Thanking again to the friend for "therapeutic persistence" I will report the results of the measures as soon as they are available, this also to help other users who are in the same situation as me (a case from what I have seen not so rare).

Crummy wrote:From another user, whom I want to thank:

Before declaring the CPU dead, check with the oscilloscope that the clock and the reset signal are generated correctly. Looking at the diagrams we see that the clock is generated by IC3 (an LS74) and the reset comes out of IC4 which is a 3 pin M51951, similar to a transistor to look at. When a digital system does not start, after checking the correct operation of the power supply outputs, you must always check the clock and reset, because many times the problem lurks there. Without these two signals, the CPU and the rest of the logics do not start and the device remains frozen.

Thanks to this precious trace, I have studied a little better the MAIN BOARD (KLM-1266) wiring diagram from the Korg Service Manual and the SN74ALS74 and M51951 datasheets with relative pinouts, naturally coinciding with those shown in the Korg wiring diagram. (It is a pity that the Scan / "Analog" typography of the Service Manual, in some places, is really hard to read).

In the next few days, as soon as possible, I put the measurement set back up with the oscilloscope and check various signals. I have already verified, previously, that the oscillation was generated from the quartz which then allows the generation, of the signal CK and then CLK. (However, I did not measure if this was at 32MHz as per diagram).

Thanking again to the friend for "therapeutic persistence" I will report the results of the measures as soon as they are available, this also to help other users who are in the same situation as me (a case from what I have seen not so rare).

Did you resolve your issue?