how to identify and discharge filter caps Nashville 112?

[Joe Shelby]

I want to do some contact cleaning on my amp.
The filter caps look like the two cylindrical cans on the circuit board closest to the power switch.
Are these the filter caps?
How do I safely discharge them once I have indeed verified that these are them?

Joe

[J Fletcher]

I have never seen the inside of one of these but if you let the amp sit for a few days , they should discharge . Also , the voltages in this amp are probably not very high , unlike a tube amp, so just make sure it's unplugged from the AC socket .

[Joe Shelby]

Thanks J.

[George Biner]

Assuming you have the amp apart, put a volt meter on the voltage supply rail in the amp that the cap is connected to, switch the amp off, watch the voltage decay below the magic number, 50V. Below that, you won't get electrocuted. Or put the meter across the cap in question. Should only take several seconds to decay, certainly not days.

[Joe Shelby]

Thanks George.

[Joe Shelby]

Can I use a cheap-o multimeter to test what George described testing- the power supply voltage rail.
I was trying to do this on the cheap to avoid taking the unit to an amp repair shop.
My amp sounds like WWIII at low volume even and I thought cleaning the contacts might be one solution.
What do you think?

Joe

[George Biner]

Yeah, any multimeter will do -- make sure you set the meter to the correct voltage range. Actually, looking at the schematic online,

https://www.audioservicemanuals.com/p/p ... ice-manual

it appears to me (please check and don't take my word) the highest voltage is +/15VDC, which is very benign, can't hurt you.

[Joe Shelby]

I'm guessing these are the ones that lead from the transformer to the caps marked C17 and C18.
I hooked up the multimeter and set it for 20 Volts.
I got a reading of 0.00 on the multimeter.
Can this be right?
Maybe I'm just out of my league...







Joe

[George Biner]

One test lead to one side of either of those caps, and the other lead to the other side of the same cap, should give 15V when amp is on. Be sure to set meter to DC voltage, not AC (AC will show 0).

[Joe Shelby]

I hooked up the multimeter to the 20VDC setting and touched the leads to each filter cap (C17, C18). No matter where I put the negative lead all I got was 0 on the multimeter. I tested the multimeter on a 9V battery and it gave a reading.
What am I doing wrong?

[Joe Shelby]

I touched the positive multimeter lead to the circuit
trace marked C17+ (and also for the cap marked C18+) and touched the negative multimeter lead to each of the traces coming out of the cap. No reading but 0.

[Joe Shelby]

Thanks Georg.










Joe

[Joe Shelby]

So here's what I did once I determined that with the
amp off it was safe to get my hands in there.
1) cleaned molex connectors (with Peavey funk out)
2) cleaned pots from the notch where they're mounted in the chassis--this was much more effective than doing it from the front of the control panel.The mid shift pot
is still kind of scratchy. It doesn't have a rear access notch like the rest of the pots.
The amp is relatively noiseless and all of the WWIII noise is gone.
I'm happy...


Joe.

[George Biner]

Well, in view of Georg's post (that 15V power rails are not enough to get 80W into 4 ohms), I looked again at the schematic that was posted on the web, and it clearly shows +/-15V rails on the output stage -- into a 4 ohm speaker that should make about 28W max output power, not 80. So I don't know why the schematic says that, it can't be right.