Recapping my M1 - PART 2

[Tekhed66]

Hi all

Firstly, thanks for the info on a previous post regarding the white gunk around the capacitors on my M1's power board... yes, it was glue... I ended up just desoldering and levering the capacitors off the PCB... it was obviously glue once you had a close up look... all of the removed caps were intact and the PCB was in good condition - no corrosion or other nasties.

Which brings me to my next sad tale of woe....

I recapped all the boards on the M1 and now it won't power up... I double checked all of the soldering and cap orientation, all of the plugs and general bits and bobs but no joy...

I removed the back of the synth and switched it on and noticed a loud(ish) buzzing noise coming from the power board... sounds like an electrical hum but I didn't leave it on long enough to check exactly what's causing it... the onboard PCB fuse is still intact, there isn't any funny electrical smell and fortunately, no blue spark or smoke (!!!!!)

To be honest, I was a little bit surprised that it didn't power up and I've done surgery on many synths over the years and this is the first one that died on the table (so to speak)... I want to check to see if there is power going to the 5V and 12V output but I'm unsure what to do... here is the power board so you know what I'm looking at:

Can anyone pls tell me which pins to check on the 5V and 12V white output plug and can I do this with a bog-standard multimeter? ... I can't afford to take it to a tech so this is a DIY kitchen table job... I just wanted to ask here first before I make a bad job even worse.

Thanks very much for your help.

[Yekuku]

Hi buddy,
first of all check the fuse.
I have noted the pins in the picture.
Good luck !

[Tekhed66]

Hi buddy,
first of all check the fuse.
I have noted the pins in the picture.
Good luck !

Hi Yekuku
Thanks for the info on the 5V / 12V pins... definitely a job for when I'm back from work!
I checked the fuse (first thing I did)... it's still OK (I was hoping it had blown if that makes sense).
Any idea what might be causing the buzzing?
I might re-cap the thing all over again and see if that helps.
many thanks

[Yekuku]

Buzzing can be caused by coils and transformers.
I think that you might broke a pad while soldering / desoldering caps.
Test pcb traces for continuity with the psu powered off.
take extra caution as these things are dangerous.

[madtheory]

I think that you might broke a pad while soldering / desoldering caps.
Test pcb traces for continuity with the psu powered off.

Yes this is what I was going to suggest also. There's a crack right where it says KLM-1269, and the bottom right corner of the PCB is cracked off as well. So a continuity problem seems the most likely.

With a picture of the other side of the PCB, we can do a visual inspection.

FWIW in the future the best rule about recapping is: if it's not broken, don't fix it. Because it's possible another component may have been over-heated in the soldering and de-soldering process, and has failed.

[Yekuku]

Well , Madtheory nailed it.
Super sharp vision you have there Mr. Thomas, very good observation!

[Tekhed66]

I think that you might broke a pad while soldering / desoldering caps.
Test pcb traces for continuity with the psu powered off.

Yes this is what I was going to suggest also. There's a crack right where it says KLM-1269, and the bottom right corner of the PCB is cracked off as well. So a continuity problem seems the most likely.

With a picture of the other side of the PCB, we can do a visual inspection.

FWIW in the future the best rule about recapping is: if it's not broken, don't fix it. Because it's possible another component may have been over-heated in the soldering and de-soldering process, and has failed.

Yekuku / Madtheory

Thanks for the info guys... funny you should say 'if it aint broke - don't fix it' ... I told a friend of mine who used to work as an electronic technician in a PCB panel repair job about my dis-repair job... his first words were 'if it aint broke...' except that the language that he used was much, much more explicit and to the point ... he is kindly coming over on Friday night to run his multimeter over the PCB and have a good look.

I saw the crack in the PCB when I dismantled it but I'm pretty sure that it it's only localised to the edge of the board though checking the continuity of the traces will be the sure bet.

The only thing I can think of - apart from accidentally cracking the board when removing the cap that was glued down - was that I have accidentally soldered the legs of the capacitor into the wrong hole... if you look carefully at the last photo where the big central capacitor is soldered, you'll see two holes right next to each other (they appear to be joined to the same trace)... the original capacitor was much wider and the legs spanned the widest gap but the new capacitor is narrower and the legs wouldn't fit... I assumed the two adjoining holes were there to accommodate different width capacitors... (have I just made a bigger fool of myself )

Well I'm not going to do any work on it until Friday night when a grown up comes over and tries to undo my mess... stay tuned and thanks again for the help

Photos of the reverse of the board as requested:

[Yekuku]

Hi tekhed,
the big central capacitor looks good , the 2 holes are for fitting different sizes of capacitors.
The problem should be on the secondary side of the power supply, can you please upload a picture showing the back side of the whole pcb (especially the area that you have worked on)? In the pictures that you took , the secondary side is missing.

[Tekhed66]

Hi tekhed,
the big central capacitor looks good , the 2 holes are for fitting different sizes of capacitors.
The problem should be on the secondary side of the power supply, can you please upload a picture showing the back side of the whole pcb (especially the area that you have worked on)? In the pictures that you took , the secondary side is missing.

Hi Yekuku

The Friday night repairs never happened... my friend is a good technician but sadly, a bit unreliable... oh well.

I've attached two photos of the entire PCB front and rear.... I was hoping to get my friend check continuity of all of the traces.. I've checked a few places on the PCB and some spots show continuity (mostly the components I didn't replace) and other parts dont have continuity (eg. across the main big capacitor but I don't know enough about electronics to know if there should be continuity across capacitor terminals or not...).

Anyway, if you see anything or can suggest any specific places on the PCB to check, that would be great.

many thanks

[Yekuku]

Hi , unfortunately I dont see any cracks.
The picture resolution is not great, but from what I see, I would reflow all worked solder joints.
To continue troubleshooting you need to measure the 5v/12v/-12v voltages of the psu.
If you are not comfortable with this , dont do it, wait for your friend to do it.
You said the synth does not power up. What happens when you switch it on, does the screen stay dark or does it light up and stays blank?

[Tekhed66]

Hi , unfortunately I dont see any cracks.
The picture resolution is not great, but from what I see, I would reflow all worked solder joints.
To continue troubleshooting you need to measure the 5v/12v/-12v voltages of the psu.
If you are not comfortable with this , dont do it, wait for your friend to do it.
You said the synth does not power up. What happens when you switch it on, does the screen stay dark or does it light up and stays blank?

Hi Yekuku

Yeah... pic resolution isn't great... I tried uploading a higher res pic but it wouldn't upload... might try a third party host next time.

I'm prepared to wait for help... fortunately, this is a synth that I hardly use so I wasn't too stressed to open it up and work on it ... I would have preferred that it worked but it's no big deal.

The synth has no power at all... screen stays dark after you switch it on so my guess is that it's the power board... I'm prepared to recap if necessary but in the meantime I'll reflow the solder as you suggested... I also can't see any cracks but would like to verify this by checking continuity across the board.

Anyway - this looks as if it's a work in progress so I'll keep adding to this post as I bumble my way along (maybe it will be of some use and/or amusement to other M1 owners) (!!??)

[Yekuku]

If the LCD stays dark then you are probably missing the 5v voltage rail , but we need to be sure about this.
I would also check diode D8 and coil L5.

[Tekhed66]

If the LCD stays dark then you are probably missing the 5v voltage rail , but we need to be sure about this.
I would also check diode D8 and coil L5.

Hi Yekuku

I checked D8 and L5 as you suggested... my multimeter shows 000 when the continuity is 100% closed/circuit closed 1 when the continuity is broken/circuit open... after checking, D8 shows 214 in one direction and 115 in the other direction (by swapping over the multimeter probes)... L5 shows 000.

I also re-flowed the solder joins again and rechecked the voltages which was very interesting...
the 5V rail now showed 7.1V and the 12V rail showed 32V... I checked the voltages by applying the multimeter probes to the two outermost (red) pins of the rail ie. | i i |

I haven't plugged the board back into the synth yet... just wanted to run these voltages past the forum first...

Puzzling...

[Yekuku]

Hmm, voltages might be ok since there is no load.
You are measuring the 12v rail wrong.
-12v : ii||

12V :||ii

Please measure these again and let me know.

[Tekhed66]

Hmm, voltages might be ok since there is no load.
You are measuring the 12v rail wrong.
-12v : ii||

12V :||ii

Please measure these again and let me know.

Ha! ... stupid me... I measured the 12V pins the same as the 5V pins.

OK - I've remeasured correctly (!?) and the new results are:
5V rail shows 7.1V
12V rail shows +/- 16V

I haven't plugged the power board back into the synth... I'm waiting to feel a bit braver first (might have to have one more beer first).... might do that tonight if I have time ... (the board, not the beer... then again a beer sounds great).

I'll post back here and let you know how things are... I'm just hoping that the problem is located in the power board... I'd hate to have to go through each of the remaining boards and look for a fault.... grrrrr

And as always, thanks very much for your help