Memorymoog Power Supply woes (solved)

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zaiusz
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Memorymoog Power Supply woes (solved)

Post by zaiusz » Wed Jan 27, 2016 7:11 pm

Hello folks, after quite some time I've taken the plunge and popped my MM open after it died years ago. It was a little daunting at first to understanding what is happening inside but the more I did my research it's all starting to make sense. I've managed to trace my problem to the 5V rail, and I've rebuilt the power supply with all new capacitors, rectifiers and all the other semiconductors. After attempting to get the 5v up I still had 0 volts even while freerunning the board measuring between pins 2&4 of p131. Eventually it occurred to me to see what's happening from the transformer, and I'm a little suspicious as to the readings I'm getting. I'm seeing 23 volts coming out of both 15+/- plugs (Red&Grey), but the yellow 5v i'm only seeing 9V. I have no idea what the output of the transformer should be on each tap, but I feel like it should be higher as I recall something said in my moog service binder-- something like the voltage at the bridge is "much higher" and the transistors and 723 do the rest.

My questions--
1. Does anyone here by chance know what the measured AC voltage typically is at each tap from the transformer?
2. If my transformer is toast, does anyone know where to get a suitable replacement??

Thank you for reading.
Last edited by zaiusz on Thu Feb 11, 2016 10:21 am, edited 1 time in total.

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noddyspuncture
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Re: Memorymoog Power Supply woes

Post by noddyspuncture » Wed Jan 27, 2016 9:22 pm

I seem to remember that you need to short the sensing lines to the relevant supply lines if you are 'free running' running the power supply...?
I recapped mine a while back and it is much the same as working on my CS80 power supply in that respect...!

Also each rail has it's own dedicated bridge rectifier. I'd start by checking the DC voltage on the rectifier output into the smoothing cap - C7. You should be seeing 11.5v DC there. If you got that voltage there then your T/X is OK.

Cheers
Tom

zaiusz
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Location: Torontoish

Re: Memorymoog Power Supply woes

Post by zaiusz » Wed Jan 27, 2016 10:42 pm

Hi Tom, thanks for the reply. So in other words I could measure between pin 4 & 5 at the raw voltage since it looks like its directly connected to the + on the cap. Will do that.

Also, I have the original service manual here with me and I don't see mention of shorting any pins to measure them.. unless thats on a service bulletin I don't have

zaiusz
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Location: Torontoish

Re: Memorymoog Power Supply woes

Post by zaiusz » Wed Jan 27, 2016 10:49 pm

Ok, when I measure between pins 4&5 I get slightly over 12 volts. So this is normal?

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noddyspuncture
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Re: Memorymoog Power Supply woes

Post by noddyspuncture » Thu Jan 28, 2016 8:20 am

zaiusz wrote:Ok, when I measure between pins 4&5 I get slightly over 12 volts. So this is normal?
You are confusing me with your pin numbers. My MM schematic tells me P131 pins 12, 13, 14 and 15 are the +5volt ones.
It says that 12 and 13 are common/ground. 14 is +5v output. 15 is +5v sensing.

Just measure across C7 - 4700/16v smoothing cap. You should be getting around 11.5 volts DC there.

Cheers,
Tom

electrojoe
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Re: Memorymoog Power Supply woes

Post by electrojoe » Thu Jan 28, 2016 10:32 am

Hi Guys,
Be careful here as the power supply markings are mislabeled.
The pin number on the physical power supply circuit board is INCORRECT.
Refer to the power supply schematic for the correct pin numbering.
For reference, if you are looking at the power supply with the connector end towards you and the components on top, pin 1 is on the left and pin 15 is on the right.

Hope this helps.

Gerry

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noddyspuncture
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Re: Memorymoog Power Supply woes

Post by noddyspuncture » Thu Jan 28, 2016 11:35 am

electrojoe wrote:Hi Guys,
Be careful here as the power supply markings are mislabeled.
The pin number on the physical power supply circuit board is INCORRECT.
Refer to the power supply schematic for the correct pin numbering.
For reference, if you are looking at the power supply with the connector end towards you and the components on top, pin 1 is on the left and pin 15 is on the right.

Hope this helps.

Gerry
This seems strange as the power supply circuit board layout diagram I also have here has pin 1 on the right and pin 15 on the left - looking at it from the same angle you mention. The pin 15 end is right next to the +5v section and the schematic says 12,13,14 & 15 are +5v related, so it would make sense... do you think that the layout diagram I have is incorrect...?

Cheers
Tom

zaiusz
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Re: Memorymoog Power Supply woes

Post by zaiusz » Thu Jan 28, 2016 12:12 pm

Hi guys, yes the diagram in the service manual is all wrong. For measuring the voltage pin 2 & 4 are 5V, 7 & 9 are 15-, and 12 & 14 are 15+. I quickly found this out while actually measuring and comparing what the SM says. There is also another section in the service manual that is all backwards for troubleshooting the power supply voltages.

Anyway, while probing around last night I noticed that I made a mistake when putting in new TIP41's. I didn't realize the heat sync on the TIP41 was in fact directly connected to the collector and the big heat sync needs to be isolated from the TIP41 using the original plastic squares that were there. The plastic squares kind of blended in with all the heat sync compound and I didn't notice it missing. This made the big sync have voltage but fixing this didn't help. Maybe this fried one of the new parts I had in there... I'll check on this later when I'm home.

zaiusz
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Re: Memorymoog Power Supply woes

Post by zaiusz » Thu Jan 28, 2016 12:25 pm

I wonder Tom if you are correct that the raw pin 5 and pin 2 (5v) need to be shorted to properly measure it. I don't see anything in the service manual about this but looking at the schematics the 5v is the only section that has a raw voltage output.

Also just to add one other thing, you can see the schematics also say the correct pinout for p131 while the circuit description in the SM is backwards. Probably because they confused themselves and started talking about the power supply in the polymoog(at least in my original printed manual, I don't see it in the scan that's available online).... no idea why they even talk about it in the first place.

**Edit-- sorry meant shorting the sensing line, not the raw 5v.

electrojoe
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Re: Memorymoog Power Supply woes

Post by electrojoe » Thu Jan 28, 2016 3:56 pm

O.K.
First, you need to have the +15 volt power section active, because, the 5 volt regulator gets it’s power from the +15 volt supply.
Second you need to connect the sensing lines for all voltages.
So for best test results, connect all 3 AC power connectors.
Using the pin numbering I suggested earlier ( Pin 1 on the left, pin 15 on the right) do the following.

Pins 1-2 connect together and that is +5 volts
Pins 3-4 connect together and that is Ground for +5 volts
Pins 7-8 connect together and that is Ground for +15 volts
Pins 9-10 connect together and that is +15 volts
Pins 12-13 connect together and that is –15 volts
Pins 14-15 connect together and that is Ground for –15 volts.

Then connect the 3 Grounds together, and use that as your test ground reference.

This should give you the voltages you are looking for.

Gerry

electrojoe
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Re: Memorymoog Power Supply woes

Post by electrojoe » Thu Jan 28, 2016 3:58 pm

Oh, and please be careful!
Double check everything.

Gerry

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noddyspuncture
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Re: Memorymoog Power Supply woes

Post by noddyspuncture » Thu Jan 28, 2016 4:10 pm

electrojoe wrote:O.K.
First, you need to have the +15 volt power section active, because, the 5 volt regulator gets it’s power from the +15 volt supply.
Not on the schematic I have.... each of the sections... +15 / -15 / +5 ... have their own AC outputs from the transformer - into separate bridge rectifiers, separate smoothing caps and regulating IC's.

Am I looking at the wrong schematic here...?
How do I upload so you can see it...?

Cheers,
Tom

zaiusz
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Re: Memorymoog Power Supply woes

Post by zaiusz » Thu Jan 28, 2016 4:15 pm

Isn't there two different revision power supplies for the memorymoog? I seem to recall reading that somewhere. On my supply if you are looking at the board with the 3 ac connectors towards you, pin 1 is labeled and on the right. +15 is on the left side of the board, the trimmer on the left affects it, -15 is in the middle, and 5v is on the right.

When I tested my voltages I had all 3 AC lines plugged in too. I can get the 15v lines working no problem, just the dreaded 5v stays at 0, don't see anything coming out of the TIP41's but see the voltage at the collectors.

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noddyspuncture
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Re: Memorymoog Power Supply woes

Post by noddyspuncture » Thu Jan 28, 2016 4:25 pm

zaiusz wrote:Isn't there two different revision power supplies for the memorymoog? I seem to recall reading that somewhere. On my supply if you are looking at the board with the 3 ac connectors towards you, pin 1 is labeled and on the right. +15 is on the left side of the board, the trimmer on the left affects it, -15 is in the middle, and 5v is on the right.

When I tested my voltages I had all 3 AC lines plugged in too. I can get the 15v lines working no problem, just the dreaded 5v stays at 0, don't see anything coming out of the TIP41's but see the voltage at the collectors.
Do you also see a set of four BR diodes next to each of the three AC input sockets...? If you do then the +5 isn't derived from the +15 as was suggested before...!

Cheers,
Tom

zaiusz
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Re: Memorymoog Power Supply woes

Post by zaiusz » Thu Jan 28, 2016 4:30 pm

noddyspuncture wrote: Do you also see a set of four BR diodes next to each of the three AC input sockets...? If you do then the +5 isn't derived from the +15 as was suggested before...!

Cheers,
Tom
Yes, I have 3 separate AC lines coming into the PS board and each have 4 MR502 diodes arranged in a bridge for each section.

The only thing in the schematic I can see is that there is some sort of connection happening from the -15 section, right after the -15 smoothing capacitor there is R24 470 ohm resistor which is between that and the collector of Q7, the MPS-U05 in the 5v section.

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