Old 25V PSU recap/rebuild?

[Golgoth]

Hello,

I am currently in the midst of recaping a 83046 compressor that had progressively lost all lower end response over the years to the point of acting as a hi-pass filter when engaged.

One channel is done and perfectly working, which is encouraging. Had to order a few caps to be able to recap channel 2 so this one is still stock with all its defectuous caps.

While testing the freshly recapped channel 1 and comparing it to broken channel 2, I remarked a noise in the background, almost inaudible without compression engaged and gain turned up, but still present when both channels are engaged (LIMIT and COMPRESSION out, just the BYPASS switch on the IN position). Said noise is too loud to be able to use the compression normally as it becomes apparent on takes where make up gain is added.

The noise is exactly the same on both channels which rules out an issue with either of their cards and leads me to believe it is coming from the PSU.
Here is that noise boosted +24db: PSU noise snippet

The PSU is a custom unit installed into the compressor some 30 years ago for 220V mains:


As I am working on that unit anyway I want to recap the PSU and possibly replace that transistor too.
I have never worked on a PSU before and have just been reading that scary "shocked by a can cap" thread!

Do you guys have any suggestion about how to possibly make the PSU better, or if it looks good enough how to work on this safely?

Thanks a lot for your help,
G

 

[Rob Flinn]

The noise snippet clip doesn't work for me.

The thing you call a transistor is actually a 7824 voltage regulator. It is just in a TO3 package rather than the more usual TO220 package. Personally I wouldn't be replacing any parts in the PSU with possibly exception of the main capacitors unless I knew they were faulty. The caps may need replacing but might be fine.

 

[Golgoth]

The noise snippet clip doesn't work for me.

The thing you call a transistor is actually a 7824 voltage regulator. It is just in a TO3 package rather than the more usual TO220 package. Personally I wouldn't be replacing any parts in the PSU with possibly exception of the main capacitors unless I knew they were faulty. The caps may need replacing but might be fine.

Hi Rob, does this link work? PSU noise
This is a stereo recording of both channels.

 

[Rob Flinn]

Hi Rob, does this link work? PSU noise
This is a stereo recording of both channels.

yes, it works. That sounds like perhaps a poor connection, or a cap.

 

[Golgoth]

yes, it works. That sounds like perhaps a poor connection, or a cap.

All connections / solder points around the PSU look great to me. I'll replace all PSU caps and report back!

 

[scott2000]

Weird...Sounds like some wireless noise almost....
But if it's always there, that probably wouldn't be the case..

Was joking with my neighbor while we were texting that it was easy to tell when he respsonded because I'd hear it coming before it got to my phone....

 

[chilidawg]

You'll get zapped if:
- you touch a bare live main AC voltage wire (such as the metal tabs on the transformer primary side), but this is only when the PSU is switched on.
- you touch the main caps' pins a second after you turned off the PSU, and this is also only if the DC voltage are very high (very unlikely since the regulator is 24V)

 

[Rob Flinn]

All connections / solder points around the PSU look great to me. I'll replace all PSU caps and report back!

Unfortunately when fault finding electronic equipment "looks great" doesn't necessarily mean anything.