I agree with others here. If you can measure the correct voltages *sometimes* and the unit begins working when they are present, it's more likely a problem with the 6-pin Molex header than the power supply. Pictures would help us guide you towards an effective repair or workaround.
Lexicon PCM-80
- Thread starter W DeMarco
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Fabriguitar
Member
Thanks Ike, thanks Radardoug!
I have found that soldering cables to Molex will be very difficult and destructive. I'm thinking of cutting the Molex and using 6 single plugs, or soldering the wires directly to the board.
The welds on the back of the board look good.
I send some photos, as recommended.
Putting my description of the problem back in order, I would like to point out that the fault occurs when I don't hear the "click" at the end of the diagnostics (it should also be heard when the machine is turned off). The "click" seems to come from the center of the main board, or perhaps the CPU board, where 5V wires arrive (and this 5V current seem to work, as the PCM does the diagnostics correctly).
The 15V wires cross the whole box and feed directly the analog section which is on the far left. This thing makes me think that some element is malfunctioning in the digital section that should unlock the 15V power supply. Could it be? Is there a relay?
P.S. I post an image of a component, cleraly marked with "made in China". It is not really important, but does it seem strange in an American machine from the 90s.
I have found that soldering cables to Molex will be very difficult and destructive. I'm thinking of cutting the Molex and using 6 single plugs, or soldering the wires directly to the board.
The welds on the back of the board look good.
I send some photos, as recommended.
Putting my description of the problem back in order, I would like to point out that the fault occurs when I don't hear the "click" at the end of the diagnostics (it should also be heard when the machine is turned off). The "click" seems to come from the center of the main board, or perhaps the CPU board, where 5V wires arrive (and this 5V current seem to work, as the PCM does the diagnostics correctly).
The 15V wires cross the whole box and feed directly the analog section which is on the far left. This thing makes me think that some element is malfunctioning in the digital section that should unlock the 15V power supply. Could it be? Is there a relay?
P.S. I post an image of a component, cleraly marked with "made in China". It is not really important, but does it seem strange in an American machine from the 90s.
Attachments
https://nl.farnell.com/artesyn-embe...45/power-supply-switch-mode-5v-15v/dp/1171467 , in stock and € 33,61
That actually looks like quite a good quality SMPS, and yes most of those are made in China and have been for years. But, they do wear out.
The "click" is a relay which most likely uses the 5v supply to activate it. So, no 5v supply = no relay = no "click". It looks like the solder joints for the Molex header are fine, but one thing I would still like to see are the pins on the 6-pin header. On the 2-pin header, you can just see a bit of the tin plating starting to flake off on one pin. In this supply, it looks like they used good capacitors (Nichicon) but they probably cut costs by using shitty Molex headers.
Fabriguitar
Member
good, if I will need to replace it, this is good information!I am attaching an image where you see 1 pin disassembled (with a bit of violence ...) from the female 6 wire connector in the background.
The wire is crimped only, but it is tightened well.
It seem ok...
Attachments
I meant the male pins, but they look ok from what I can see in the background. I haven't seen this mentioned yet but I have encountered this often in SMPS: There is a small cap, usually 47-100uf, near the front end of the supply that can go high ESR but still read the correct value in uf. I am by no means well versed in the design of these supplies but it is my understanding that that cap is part of the start-up circuit and when they go high ESR they can not operate at the high frequencies required for the switching to take place. This failure mode is very common in devices that have been running 24/7/365, and that fail to power up after having been turned off for some reason (maintenance, power failure, being sold etc.). So, the device runs for a long time, that start-up cap goes high ESR...but the device keeps running because that cap is not needed once the supply is running, so the fault only appears after the device has been powered off. Another symptom of this issue is that the device may power up after several attempts, or after being left alone with the power switch turned on for a while.
Fabriguitar
Member
Thank you Ike, I think that my Lexicon's history should be different. It was long time owned by a big professional live service, so it had to be started and stopped every day. I can not know exactly... Anyway the behavior is very compatible with the problem you described.
At this time I've reassembled all, and it temporary works again. It's not predictable, but I'm not a professional user, can accept it (for a short time).
In next days I'll try to find a new Molex female (if I don't find, i will solder wires to board).
Further, if it doesn't resolve, think I will buy a complete PSU like the one shown linked here. It's worth doing a $ 33 repair before I start soldering (without being a good technician ). Sending the gear to service would cost a lot more (and I know repairers often consider old gears just obsolete, don't struggle to find quality components, etc etc). Instead it is very nice sounding: old but perky.
Thanks again to anyone contributing to my understanding of some ways to resolve. I will let you know the results
Ciao
Fabrizio
At this time I've reassembled all, and it temporary works again. It's not predictable, but I'm not a professional user, can accept it (for a short time).
In next days I'll try to find a new Molex female (if I don't find, i will solder wires to board).
Further, if it doesn't resolve, think I will buy a complete PSU like the one shown linked here. It's worth doing a $ 33 repair before I start soldering (without being a good technician
). Sending the gear to service would cost a lot more (and I know repairers often consider old gears just obsolete, don't struggle to find quality components, etc etc). Instead it is very nice sounding: old but perky.Thanks again to anyone contributing to my understanding of some ways to resolve. I will let you know the results
Ciao
Fabrizio
Rob Flinn
Well-known member
The click you hear on power on is a relay that time delays connecting the output sockets. this stops a load of digital crap coming out on boot up. The power supply is quite easy to replace. I did this over the summer for a client who had PSU issues on his pcm80. It is generic & there are a few manufacturers to choose from. The one I got was a drop in replacement & from memory (not so good nowadays) it was maybe £30-35 uk.
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