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Several issues with Korg M1
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computerchemist1



Joined: 02 Oct 2016
Posts: 6
Location: Warrington, UK

PostPosted: Mon Oct 03, 2016 9:15 pm    Post subject: Reply with quote

Wow, thanks for all the tips T3! I didn't think to scope the PSU rails, I went straight in the deep end looking at pulses on the DAC!
With my oscilloscope, I'm reading about 40mV P-P ripple with reference to the local ground for both the +12 and -12v at the DAC board connector CN12A. Is that about right for a 1988 design? It does feel a little high, so I'll check out the ESR on C18/19/23/21 on the main PSU. I might as well look at C22/23 on the 5V while I'm there, does that sound like a plan?
I'm seeing exactly -11.8V and +11.78V at CN12A on the DAC board measured with my Fluke ( only a year old, so I trust that figure at the moment). So, "nearly" perfect, but yes, not quite 12V.
Across R80, there is a 1.146V drop. Across R79, 1.125V drop.
Across R83, 1.039V drop, R84 1.137V drop.
-9.52V at pin 28 of the DAC, 9.58V at pin 26.
I see where you're going with the voltage drop, if there is excessive current flowing through those caps that would certainly bring the rail down, good call. I just thought I'd post this first before I dive in again, I think I've got enough spares to swap out the caps. There's no leakage on any that I can see, but of course that's no guarantee of anything!
I'll post back as soon as I've done a cap swapfest of all the caps in the sub psu and the main PSU. I'll also have a closer look at those 4 resistors too. Plan? I'll give an update soon and thanks again for the pointers!
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T3owner
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Joined: 17 Jun 2011
Posts: 368
Location: USA

PostPosted: Mon Oct 03, 2016 10:53 pm    Post subject: Reply with quote

computerchemist1 wrote:
Wow, thanks for all the tips T3! I didn't think to scope the PSU rails, I went straight in the deep end looking at pulses on the DAC!
With my oscilloscope, I'm reading about 40mV P-P ripple with reference to the local ground for both the +12 and -12v at the DAC board connector CN12A. Is that about right for a 1988 design? It does feel a little high, so I'll check out the ESR on C18/19/23/21 on the main PSU. I might as well look at C22/23 on the 5V while I'm there, does that sound like a plan?

That's a reasonable approach. Ripple at 40mV P-P isn't bad, I've seen it a lot higher when the caps go low in value and/or high ESR. Switching hash gets cleaned up further on the KLM-1261, by LC2/C50/C51 and LC1/C48/C49.

 
computerchemist1 wrote:
I'm seeing exactly -11.8V and +11.78V at CN12A on the DAC board measured with my Fluke ( only a year old, so I trust that figure at the moment). So, "nearly" perfect, but yes, not quite 12V.
Across R80, there is a 1.146V drop. Across R79, 1.125V drop.
Across R83, 1.039V drop, R84 1.137V drop.
-9.52V at pin 28 of the DAC, 9.58V at pin 26.

Assuming the 5 volt supply looks relatively clean (or if you've checked C22/23 and replaced if needed), see what its voltage measures. Adjusting VR1 affects all of the supply outputs - you can bring up the +/-12v a bit as long as the "5 volt" doesn't go above 5.1v or so. However, I don't think that 11.8v is the cause of your problems.

 
computerchemist1 wrote:
I see where you're going with the voltage drop, if there is excessive current flowing through those caps that would certainly bring the rail down, good call. I just thought I'd post this first before I dive in again, I think I've got enough spares to swap out the caps. There's no leakage on any that I can see, but of course that's no guarantee of anything!

I wasn't anticipating physical leakage, but the possibility of them being electrically leaky. Another possibility, of course, is capacitance being low or high ESR, either of which can reduce decoupling - I'd suggest scoping points [G]/[H]/[J]/[K] to verify that the caps are doing the job. Excessive noise at those points can couple from stage to stage.

 
computerchemist1 wrote:
I'll post back as soon as I've done a cap swapfest of all the caps in the sub psu and the main PSU. I'll also have a closer look at those 4 resistors too. Plan? I'll give an update soon and thanks again for the pointers!

You're welcome, and best of luck with the repair.
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Korg: T3EX, 05R/W | Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Fender Chroma Polaris | Roland U-220 | Etc.
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computerchemist1



Joined: 02 Oct 2016
Posts: 6
Location: Warrington, UK

PostPosted: Tue Oct 04, 2016 9:41 pm    Post subject: Reply with quote

A little update: I have changed all the caps in the sub PSU area on the DAC board. I discovered that C57 on the positive rail had an ESR of 4.7R and C56 on the negative rail had an ESR of 3.4R. They are now replaced as are their brethren with caps all having an ESR less than 0.2R. I also replaced R80/79 and R83/84 with 1/2W resistors, maybe a little overkill but the tiny little 1/8W really looked a little roasted. I also swapped R81/82 for 1/4W on the same basis.
The bad news: it's pretty much the same as before. Same garbled noise on keypress Sad
I now measure -9.53V at pin 28 of the DAC, 9.62V at pin 26. Voltage drops are still about the same: R80=1.077V, R81=1.114V; R83=1.053V, R84=1.13V.

Quote:
I'd suggest scoping points [G]/[H]/[J]/[K] to verify that the caps are doing the job

G/H and J/K have about the same amount of noise, somewhere between 10mV and 30mV peaks.

Quote:
Assuming the 5 volt supply looks relatively clean (or if you've checked C22/23 and replaced if needed), see what its voltage measures.

The 5V rail is 5.086V on the main board. Ripple/noise is very low on the 5V rail, I only have a DS203 and I can just see very slight movement there on 50mV/div (the most sensitive setting).

However ripple/noise on the 12/-12V rail is still around 30mV (it does seem slightly lower). Do I need to look at the smoothing caps on the PSU next, specifically those on the 12/-12 side (C23/18/21/19)? They are all Nichicon VX(M) which I believe is something like a Panasonic FC/FM? I'm guessing as it's a switched mode these are much more superior at noise rejection and ripple flattening as well as having very low ESR than the run of the mill caps.

Do you think it's still worth pursuing the PSU first before getting too deep into the guts of the CPU board?

I would kill for some accurate voltage measurements and scope traces from a completely working M1 overlaid on the schematic, it's a shame the service manual doesn't have any of those!
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T3owner
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Joined: 17 Jun 2011
Posts: 368
Location: USA

PostPosted: Wed Oct 05, 2016 3:37 am    Post subject: Reply with quote

computerchemist1 wrote:
[...]Do you think it's still worth pursuing the PSU first before getting too deep into the guts of the CPU board?[...]

Sorry, busy day, first chance I got to reply.

It's always good practice to replace caps with questionable ESR, and resistors that show signs of stress, even if they're on value. Having done that, and finding reasonable ripple levels, it's probably time to look beyond the PSU. Have you seen this thread?...
http://www.korgforums.com/forum/phpBB2/viewtopic.php?t=99451
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computerchemist1



Joined: 02 Oct 2016
Posts: 6
Location: Warrington, UK

PostPosted: Mon May 15, 2017 8:44 pm    Post subject: Reply with quote

Just in case someone finds this thread again in the future. In the end, I gave up trying with the keyboard, and bought another (working) M1 at the right price.

And the first thing I did after getting my "new" shiny working purchase back was to rip the back of it and do some comparisons.

The only thing I could really tell from voltage measurements is everything was indeed fine and consistent between "old" and "new" keyboards.

The big difference was around the inputs to the DAC. They were positively jumping all over the place on the "new" one on all data lines. So the problem appeared to be the logic board's outputs to DAC - or at least that was what I observed.

As a last final "gotcha" I briefly swapped the logic board from "new" to "old" - and "oldie" all worked fine, including the key that didn't work with "old" logic board. So I in one fell swoop ruled out wiring looms, keyboard, PSU, front panel controls, Display, DAC and expansion card PCBs.

So I came to the conclusion there were at least two things wrong on the logic board - the keyboard LSI controller and something between the sound generation and the DAC.

In the end I sold it for what I paid for it to someone who wanted the spares "in case" his M1 ever developed problems - after I pointed out other than the "Brain" it was all OK, he was a happy bunny!

I'm definitely bitten with the early M series now. I just bought an M3R... as a parting shot, can anybody point me at a schematic for the M3R?
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Gunter



Joined: 27 May 2017
Posts: 1
Location: uk.

PostPosted: Sat May 27, 2017 7:07 pm    Post subject: Reply with quote

Hi , There , I have recently have brought a korg m1 as I wish to add some new sounds ,However I must say I find the unit very complicated.I have fitted a new battery and loaded the factory sounds. I dont no how to work the unit and would welcome some advice .Thankyou.
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T3owner
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Joined: 17 Jun 2011
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PostPosted: Sat May 27, 2017 8:00 pm    Post subject: Reply with quote

Gunter wrote:
Hi , There , I have recently have brought a korg m1 as I wish to add some new sounds ,However I must say I find the unit very complicated.I have fitted a new battery and loaded the factory sounds. I dont no how to work the unit and would welcome some advice .Thankyou.

If you don't have the Owner's Manual, you might want to download a PDF version and get a general idea of the M1's operation...
http://www.synthfool.com/docs/Korg/Korg_M1_Owners_Manual.pdf

Then, I'm sure you'll have more specific questions which we can answer.
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mediterrano



Joined: 26 Nov 2020
Posts: 6

PostPosted: Thu Nov 26, 2020 5:34 pm    Post subject: Reply with quote

I want to load in new sounds to M1 using FLEX Editor but the buttons and keys of my M1 are all dead/sticky/corroded, therefore I can’t follow the below instructions to swith M1 to SysEx receive mode.

Set your M1 as follows in the global section:
Midi channel to 1
Memory protects to OFF
Midi filtering excl: ENA; 100/100 mode

Is there anyway to remotely enable M1 to receive “Bulk Dump” or “Sysex Dump”?

Maybe by sending some MIDI or SysEx messages from Midi-OX?...
If not, my M1 is pretty much useless without repairing/replacing the buttons
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MauriceFitz



Joined: 01 Feb 2022
Posts: 2
Location: Ireland

PostPosted: Tue Feb 01, 2022 5:29 pm    Post subject: Korg Mini upload of orginal factory settings. Reply with quote

I have directly contacted KORG about the issue regarding the problems with the legacy data transfer. As follows: "SysEX data dumps with non-well know brand midi cables make it impossible to restore an instrument's factory data via midi". The also suggest buffer sizes of "1024 to 2048". My opinion is that M1 should have come with the original cards MPC00P and MPC 00S in the box and mine didn't.....? The is intriguing. They said nothing when I mentioned the issue of absent program and sequence cards which now appear to be so crucial given the problems flashing the M1 with USB midi data. Other than to say that these "cards are no longer available". They are for sale on the web alright for rip-off prices. I would like to know where they got them and were they in the box when they got the work station...? The buffer sizes are also an issue they direct me to, but surprising the buffer sizes KORG suggest are only suggestion. The cable seems to be the big issue now. Buy one for 10 bucks and then buy another one three times the price in the hope it might work. You know something: one is likely to spend more time solving troublesome technical problems and snags with musical gear than actually playing and they wonder why the art of songwriting is almost dead!

Disclaimer: I am not responsible in any way for this opinion and its use to solve problems with the KORG M1 workstation. It is my own personal experience.
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MauriceFitz



Joined: 01 Feb 2022
Posts: 2
Location: Ireland

PostPosted: Tue Feb 01, 2022 5:30 pm    Post subject: Korg Mini upload of orginal factory settings. Reply with quote

I have directly contacted KORG about the issue regarding the problems with the legacy data transfer. As follows: "SysEX data dumps with non-well know brand midi cables make it impossible to restore an instrument's factory data via midi". The also suggest buffer sizes of "1024 to 2048". My opinion is that M1 should have come with the original cards MPC00P and MPC 00S in the box and mine didn't.....? The is intriguing. They said nothing when I mentioned the issue of absent program and sequence cards which now appear to be so crucial given the problems flashing the M1 with USB midi data. Other than to say that these "cards are no longer available". They are for sale on the web alright for rip-off prices. I would like to know where they got them and were they in the box when they got the work station...? The buffer sizes are also an issue they direct me to, but surprising the buffer sizes KORG suggest are only suggestion. The cable seems to be the big issue now. Buy one for 10 bucks and then buy another one three times the price in the hope it might work. You know something: one is likely to spend more time solving troublesome technical problems and snags with musical gear than actually playing and they wonder why the art of songwriting is almost dead!

Disclaimer: I am not responsible in any way for this opinion and its use to solve problems with the KORG M1 workstation. It is my own personal experience.
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