White noise in a console module, please help!

n

Look for a short to ground on the buses. That would make the sum amp run at full open loop gain.

JR

user 37518,
In addition to looking for bus shorts to ground as JR mentioned, also look for buses shorted to each other.
If both L & R buses are giving you the same white-noise, you may have mistakenly tied their bus connections together
while doing the re-capping.

JP

Pops usually indicates DC in audio path.

Best,

/Dave

Again if the buses are shorted the very high gain will amplify small dc offsets resulting in significant DC on the outputs.

JR

Ok i understand, on what should i focus my attention i mean its like a very symetrical module, 1 opamp per gain stage, 2 metal can transistors per opamp (1 NPN 1 PNP), bypass caps already replaced, and 4 resistors per gain stage, that basically it. Already replaced the opamps on the buffers, electrolytics are all in correct polarity, i measured voltage and all transistors (placing voltmeter probe on the metal can) and they all measure around -30 or 30v depending if its the NPN or PNP, tantals in logic section are new also (4 of them). And i just basically explained my entire module to you, theres a logic section but that controls an area that doesnt seem to have any problems. What else could be ?

I suspect workmanship.  You have inadvertently either shorted or lifted something crucial while doing the recapping.  It may be difficult to locate.

check for lifted pads, solder bridges, etc. all really tiny things that you sometimes need a magnifying glass to see well(at least for me sometimes)

nothing to really add here other then one should have  a magnifying lens  on the test/fix bench for just such an occasion, it comes in really handy. Especially when you are having to fix someone else's repair job and they unsoldered and resoldered parts like a caveman.

When you are so involved with something, you can miss a boo-boo even with a loupe.  Actually, a loupe is too close IMO.  Have a friend go over it with the $20 Staples magnifying lamp.  Your description looks like DC shorting somewhere, like only one rail making it to the chips.

If you don't have an extender, you can remove modules on either side to trace signals.

If the problem was there before the re-cap, then you are going to have to go to the schematics and look at all the vitals (voltages) first before picking possible faulty components.  I would not suspect a volume pot to cause this.  Maybe a 4 way pot in an EQ circuit, but not a volume pot.  Then take a trip through the circuits- patch OSC into an external input and trace the point of it's demise.
I recon that one of your audio rails is not making it to the IC's
Mike

craptical said:

Pops usually indicates DC in audio path.

Best,

/Dave

Click to expand...

Not faulty relays. 

user 37518 said:

Well i did the replacement and i was really careful but ill check it out, im not perfect , thanks for all your replies guys, ill check the module with a magnifying glass, and ill let you know, in the meantime if anyone has another idea, please let me know

Click to expand...

When electronic circuits are misbehaving I find it easier to test with a VOM...  With power off you can check for shorts where they shouldn't be, and inadvertent opens.  With power connected check opamps for power present at power pins and valid voltages at inputs and outputs.

I often find solder problems after diagnosing electrically that something isn't as it appears. Many times I find a joint that looks good but isn't or vice versa.

JR

user 37518 said:

Actually i didnt test the module before the recap, i just saw a lot of bloated and puffed capacitors so i decided to replace them all before anything, i think this was with the module before even changing the caps, ive changed a lot of caps in my console, entire modules, and almost in all of my gear, and never had a workmanship error on any of them, im very careful with my stuff although sometimes ill forget to cut some leads on new components but this is not the case, everything is double checked since that last time i forgot to cut the leads.


Im running out of ideas here, ill try to take all of the modules out of the console and leave only the master section in and see what happens, but i dont think thats it.....

Im back to where i started

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Aha!  Important information hitherto undisclosed!  So there could be plenty wrong with this having nothing to do with your changes.

Pretty much just need to do signal tracing, power rail checking, continuity checking as discussed above.  A process of elimination, which needs to be well-informed by a knowledge of the circuits and their functions.

congrads.  Make sure the switch is actually working and not just a burned out bulb. I have had it happen enough times were the switch is working perfectly but the bulb in the switch is burned out or not seated properly. Happens alot with those eao series one switches...