Recapping my M1 - PART 2

Pulling out your hair? Don't know what to do or where to go? Ask in here.
Forum rules
READ: VSE Board-Wide Rules and Guidelines

If your Help request has been solved, please edit your first post in order to select the Image Topic Icon to let others know your topic has been solved.
User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Tue Jan 19, 2021 11:32 am

The voltages are a bit on the high side, but there is no load on the PSU , so the chances are that the PSU is ok.
In order to be 100% sure , you have to add a load and measure the voltages again.
According to my thread from more than a decade ago :
I have disconnected the power supply from the main board and I have found out that the cn9 connector outputs 7.9 Volts instead of 5V and the cn12 connector outputs 17 Volts instead of 12V. Could this be the cause of the problem ?
I have connected the mainboard back to the psu and measured 4.99V for pins 1-2 of the cn9 connector and 12.05V for pin 1 of the cn12 connector BUT only 1.85V for pin 4 of the cn12 connector.
According to my previous findings I think that the PSU is ok, but dont trust strangers, you should put a load and check voltages.
If you are feeling brave, connect it to the mainboard and measure the voltages as quickly as you can, if sth is on the high side , power off immediately.
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Tue Jan 19, 2021 12:13 pm

Yekuku wrote:
Tue Jan 19, 2021 11:32 am
The voltages are a bit on the high side, but there is no load on the PSU , so the chances are that the PSU is ok.
In order to be 100% sure , you have to add a load and measure the voltages again.
According to my thread from more than a decade ago :
I have disconnected the power supply from the main board and I have found out that the cn9 connector outputs 7.9 Volts instead of 5V and the cn12 connector outputs 17 Volts instead of 12V. Could this be the cause of the problem ?
I have connected the mainboard back to the psu and measured 4.99V for pins 1-2 of the cn9 connector and 12.05V for pin 1 of the cn12 connector BUT only 1.85V for pin 4 of the cn12 connector.
According to my previous findings I think that the PSU is ok, but dont trust strangers, you should put a load and check voltages.
If you are feeling brave, connect it to the mainboard and measure the voltages as quickly as you can, if sth is on the high side , power off immediately.
That's really interesting Yekuku (btw - I didn't know you had previously posted on the forum regarding this topic... how freaky!).

I'm surprised to see that your measured non-loaded PSU voltages were 7.9V (instead of 5V) and 17V (instead of 12V)... they're very close to my measured voltages (7.1V and 16V, respectively).

Well I'm having that beer so I think I'll just think about it for a bit more but I'm going to reassemble the boards tomorrow and remeasure/reboot... maybe the PSU was OK after all and the problem lies in another board? I'll know tomorrow...

I'll post again with either good news or bad news... cheers for now.

User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Tue Jan 19, 2021 3:26 pm

In a situation like this , it is recommended to have the multimeter probes already in place before switching on .
Instantly , switch on and take readings then power off and go to the next voltage rail.
What you dont want to see is more than 6V on the 5V rail, this could be bad news for the digital ICs. The other voltage rails ( 12,-12V) can withstand some overvoltage without blowing sth.
good luck buddy !
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Thu Jan 21, 2021 8:48 am

Yekuku wrote:
Tue Jan 19, 2021 3:26 pm
In a situation like this , it is recommended to have the multimeter probes already in place before switching on .
Instantly , switch on and take readings then power off and go to the next voltage rail.
What you dont want to see is more than 6V on the 5V rail, this could be bad news for the digital ICs. The other voltage rails ( 12,-12V) can withstand some overvoltage without blowing sth.
good luck buddy !
Hi Yekuku

Well I got brave and plugged the PSU back into the synth... in the end I didn't check the synth PSU voltages under load because the keyboard didn't even power up... there is definitely power going to both the 5V and 12V rails but the synth is dead (for now)... not even a flicker.

My technician friend who used to do these sort of diagnostic repairs for a telecommunications company said it's quite common to have a few more volts up your sleeve when a PSU isn't under load... funnily enough he also has an M1 so I'm hoping to use his as a guide when I go hunting for the fault in mine.

The fact that there's power to the PSU rails means the fault lies deeper in the synth and on another board... I might just pull the whole thing apart once again and rebuilt it from scratch (checking / reflowing all my solder joins and checking cables along the way)

It's frustrating but not the end of the world... though it would have been nice to see that thing light up... anyway, I'll probably leave it for a few days and get back to it later in the weekend... grrrrrr

stay tuned for updates :mrgreen:

User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Thu Jan 21, 2021 10:03 am

Could it be that a cable is not properly connected to the main board ?
The PSU looked good, but we need to measure voltages with load in order to figure out whats going on.
My guess is that the 5V line does not go to the mainboard or the 5V is down due to a short / failing component.
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Thu Jan 21, 2021 11:33 am

Yekuku wrote:
Thu Jan 21, 2021 10:03 am
Could it be that a cable is not properly connected to the main board ?
The PSU looked good, but we need to measure voltages with load in order to figure out whats going on.
My guess is that the 5V line does not go to the mainboard or the 5V is down due to a short / failing component.
I'm was hoping it was something as simple as a bad cable but I unplugged the 5V cable and tested it... all OK (didn't do the 12V cable).

I'm going to disassemble the synth and go over it again... my tech friend said he could help but won't be able to come to my house for at least another week as he is taking his family on holiday for a while... no big deal.

I'll check the 5V supply at the motherboard connector and see what is happening there...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Tue Jan 26, 2021 11:00 am

Yekuku wrote:
Thu Jan 21, 2021 10:03 am
Could it be that a cable is not properly connected to the main board ?
The PSU looked good, but we need to measure voltages with load in order to figure out whats going on.
My guess is that the 5V line does not go to the mainboard or the 5V is down due to a short / failing component.
Hi Yekuku

Well good news and bad news and some very embarrassing news...

I fixed the M1 and got it working again... I stripped it down, rechecked the soldering, checked the cables and carefully reassembled it... then I discovered why it didn't work and what a stupid thing I accidentally did :o

When reassembling it for the first time, I accidentally swapped the 5V and 12V cables over so that the main board received 12V and the AD board received 5V.... aaarrgghhhhhhhh!!!!!!!!!!!!!!!!

The synth now works except that the output signal in the L channel is very low... I can only just hear something in headphones and the 1/L output jack only gives a signal if the main volume is set to maximum... the R channel is fine... nice and clear and loud in both headphones and from the 2/R output jack...

What a careless thing to do... I had accidentally mislabelled the cables when I took it apart and thought that everything was OK when I pieced it back together.

I can still use the keyboard (I only ever used it with the 1/L output jack anyway)... it just makes me annoyed that I botched such a simple job...

On the bright side, the new tactile switches are fantastic :D

Just out of interest, would you know if something like this (cooked MB and low output) is something that can be fixed?... and where to start?????

Oh well... you live and learn...

User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Tue Jan 26, 2021 2:41 pm

Tough luck buddy :-/
You are lucky you did not fry sth on the dgital section, sounds like the analog section has the problem.
What you need to do is get an oscilloscope or an audio signal tracer, and track the output from the DAC.
My guess is that you have audio output from both L & R outputs of the DAC, but in the way to the output jacks the left channel is lost. This could be a failing opamp between the DAC and the outputs.
For start you should inspect connector CN13 :
-PIN2 is ground
-PIN4 should be L ( or right)
-PIN5 should be R (or Left)
Listen to these pins and check if one channel is louder than the other.
If yes, the problem is between the DAC and the CN13
If no, the problem is between CN13 and the L output jack.

Edit : are you sure that the volume slider is working correctly ? could it be that the sliders left channel is bad?
If you apply vertical pressure on the fader, does this have an effect on the volume of the L channel?
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Wed Jan 27, 2021 3:03 pm

Yekuku wrote:
Tue Jan 26, 2021 2:41 pm
Edit : are you sure that the volume slider is working correctly ? could it be that the sliders left channel is bad?
If you apply vertical pressure on the fader, does this have an effect on the volume of the L channel?
Hi Yekuku

Thanks for the info ... I have a friend who owns an oscilloscope so I'll borrow it and see what damage I've done.... I'm still kicking myself over such a stupid mistake... oh well...

To answer your questions, I think the volume slider is OK... I've pressed it down as suggested as well as wiggling it, bashing it and swearing at it and it doesn't have any effect... the L channel is still very low (so low that you have to turn the volume to max in order to hear anything).

I'll check that chip as suggested and maybe that will help... out of interest I looked for second hand DA boards on the web and I've found 2 available.... for a synth I hardly ever used, it sure is costing me time and a few dollars (!!??)

cheers :-)

User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Wed Jan 27, 2021 7:43 pm

I thought of what could have been damaged when you connected the plugs wrongly, and a fault on the analog section makes no sense since you connected 5V to the 12V line. There was no overvoltage and no overcurrent, but some kind of shorting 12v & ground to 5V, which shouldn't cause an opamp to fail.
By connecting 12V to the 5V you could have fried a lot of things on the digital section, but since the unit boots up, it looks like everything is ok there.
I believe that it could be the volume slider.
When assembling /disassembling , you put the unit upside/down and apply pressure to screw / unscrew.
Due to the front panel shape of m1 , a lot of pressure is applied to the volume slider and it can get easily damaged.
Before using oscilloscope or signal tracer , rule out the slider first.

Edit: you can try bypassing the slider and check if left channel plays at full volume.
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Thu Jan 28, 2021 1:23 pm

Yekuku wrote:
Wed Jan 27, 2021 7:43 pm
I believe that it could be the volume slider.
When assembling /disassembling , you put the unit upside/down and apply pressure to screw / unscrew.
Due to the front panel shape of m1 , a lot of pressure is applied to the volume slider and it can get easily damaged.
Before using oscilloscope or signal tracer , rule out the slider first.

Edit: you can try bypassing the slider and check if left channel plays at full volume.
I was thinking along the same lines ie. only 5V went to the 12V DA board so nothing too serious could have happened there...

The volume slider??? Really?... that would be like dodging a bullet if that were the case... well ruling that one out is a good place to start... the Right channel is clean, loud and isn't distorted while the left channel also sounds clean but has a very, very low output in both the headphone jack and main 1/L jack... I'll give it a go.

Fingers crossed!

User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Thu Jan 28, 2021 5:54 pm

In order to bypass it you need to connect a wire from the Left channel input of the slider to left channel wiper.
Sorry I have no pic about this.
If you are unsure about it , connect a signal tracer or oscilloscope to the Left channel input of the slider and compare it to the right input of the slider. it should be full volume on both.
Good luck!
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - PART 2

Post by Tekhed66 » Mon Feb 01, 2021 1:17 pm

Yekuku wrote:
Thu Jan 28, 2021 5:54 pm
In order to bypass it you need to connect a wire from the Left channel input of the slider to left channel wiper.
Sorry I have no pic about this.
If you are unsure about it , connect a signal tracer or oscilloscope to the Left channel input of the slider and compare it to the right input of the slider. it should be full volume on both.
Good luck!
Hi Yekuku

This is taking a bit longer to diagnose than I thought... we've just gone into Covid lockdown again so it's impossible to get hold of an oscilloscope and the only tool that I have available is my trusty old multimeter...

I tried checking the resistance of the potentiometer as I swiped it up and down (from min to max vol) ... (I think) one of the channels showed 0 to 19 kOhm and the other showed 19 kOhm no matter where the volume was...

I'm not sure if I measured this correctly though as I may have used the wrong contacts ... would it be possible for you to tell me which PCB contact points I should check in order to either bypass the potentiometer completely (as you suggested) or to test whether the potentiometer is working?

I hope to get hold of an oscillosope next week assuming we're given the all clear.... will post back here and let you know.

many thanks :-)

User avatar
Yekuku
Active Member
Active Member
Posts: 735
Joined: Tue Nov 18, 2008 11:29 am
Gear: dk'tronics speech synthesizer :P
Location: Greece

Re: Recapping my M1 - PART 2

Post by Yekuku » Mon Feb 01, 2021 9:37 pm

Hi buddy,
try these steps
1. remove slider
2. connect/solder the 2 contacts in the green circle ( OUT 2 in schematics, should be Right channel)
3. connect/solder the 2 contacts in the red cycle.( OUT 1 in schematics, should be Left channel)
if you choose to skip step 1 , set slider to full volume.
Main output should have full volume
Attachments
M1 volume bypass.jpg
It is all about sharing...

User avatar
Tekhed66
Junior Member
Junior Member
Posts: 197
Joined: Thu Jun 04, 2015 6:59 am
Gear: Roland JD990 / JD800 / XV5080 / SH-01a,
Behringer DM12, Korg Triton Rack / M1 / Radias,
Akai s5000, Yamaha An1x, Kawai K5000s,
Studiologic Sledge 2
Band: The Creepy Uncles
Location: Australia
Contact:

Re: Recapping my M1 - SOLVED

Post by Tekhed66 » Fri Feb 05, 2021 6:39 pm

Yekuku wrote:
Mon Feb 01, 2021 9:37 pm
Hi buddy,
try these steps
1. remove slider
2. connect/solder the 2 contacts in the green circle ( OUT 2 in schematics, should be Right channel)
3. connect/solder the 2 contacts in the red cycle.( OUT 1 in schematics, should be Left channel)
if you choose to skip step 1 , set slider to full volume.
Main output should have full volume
Hi Yekuku

Well I never thought I'd be posting this but the M1 is now fixed and working perfectly... what a relief!!

It turns out that it was all due to bad soldering on my part :oops: ... my technician friend came over and we methodically went through the boards with his oscilloscope, working back from the jack board until we found the source of the problem on the DA board which was a dry joint on one of the capacitor legs on the output 1 channel of the DA board.

To recap, I had no signal out of output 1, clear signal from output 2 and none from 3 and 4 (that I could tell)... we worked out that output 1 had the bad joint even though it looked OK... with a bit of wiggling, we sometimes got a signal and sometimes not and that gave us a clue... to be sure, we reflowed all the recapped capacitor connections on the DA board and when we tested it, everything came back to life. We realised that the lack of output on channel 3 and 4 must have been because of a programming error (ie. nothing was allocated to ch 3 or 4 as the main output) which meant ch 1 was broken, ch 2 was OK and ch 3 & 4 were also working but muted.

The 12V load into the 5V board didn't do any damage and he thinks that may have been because I simply switched the synth on and off without playing anything through the synth or perhaps just because I was very lucky.... the jury is still out though it makes you think that a lot of these old components are much stronger than you realise (or are stated in the service manual).

I'm pretty sure that the power board also had a dry joint as there definitely wasn't any voltage from the 5V or 12V rail when I made my first repairs many weeks ago... I reflowed those joints which fixed the problem so we figured the problem would be hiding in either the motherboard or the DA board.

Anyway - whichever way you look at it, I think I was lucky to get away without damaging the synth and after having recapped and replaced all of the switches, there's no need to open it up again so hopefully, that's the end of the story.

I just want to thank you for all of your help and advice through this... I learnt quite a lot about the synth and really appreciated your advice and interest in trying to get it working again... hopefully this drama might stay in the forum archives and help someone else out in the future... just remember to correctly and carefully label your cables and be careful of those 5V and 12V power supply cables that sit next to each other and look almost identical (and triple check your soldering!!!!)

That's enough excitement for now....

thanks again
tekhed :D

Post Reply