Memphis 16-mcd1000.1

[rhempz01]

I working on a Memphis for someone and one of the safety caps is completely burnt up and I need the value. C240.

 

[Perry Babin]

2.2uF@100

 

[rhempz01]

I found this in a old Memphis board, 225k100 will it work?

 

[Perry Babin]

That's the right cap.

 

[rhempz01]

The amplifier is up and running however it seems that something is wrong with one or more of the drivers on the output daughter board, something on the card is exceeding 140° f. Comparing the other card its highest temp being only 110°f

 

[Perry Babin]

There are 3 large drivers on the card. Are all 3 overheating on the hotter card?

Have you tried looking at the output with only one car installed at a time to see if there is distortion for one card? Swap sides to confirm that the problem follows the card.

 

[rhempz01]

both driver cards are the same in either side the output remains the same. a high pitched sqeal emittits overtop the audio. regulated voltage is good no opamps seems to be heating up. One of the 33uF 200 NP caps seem to be getting hotter than the other. there is
-0.055vdc at the speaker terminal

 

[Perry Babin]

How does the waveform on the drain of the outputs compare from one side to the other?

 

[rhempz01]

from main ground or rca sheild?

 

[rhempz01]

even after its shut off itt continues to make a sound from one of those caps i beleive. both of them are non polor 33uf 200v correct?

 

[Perry Babin]

Are you saying that with no power applied that the cap itself is making a noise?

I'm not sure that I understand #9. If you're asking where to ground your scope, leave its ground connected to the 12v power supply ground unless you have a reason to use a different ground (rare).

 

[rhempz01]

Yes perry the cap was making a sizzling scary type noise so I pulled them again. And now they are failed, they were also damaged badly at the initial year down but tested within tolerance so I reused them until I could find replacements. I am having a difficult time finding non-polar 33uF 200v replacements.

 

[Perry Babin]

I use 10uf film caps to replace these. If you have the tutorial, the part numbers are given on the 'type 1' page.

That said, I think that one of the inductors is shorted and that's killing the caps.

 

[rhempz01]

one of the large round ones or the smaller 8uH ones? i have a old board with a 10uF 200V set of caps in it, if those will work?

 

[Perry Babin]

One of the large ones.

The 10uf will work but if you install them with a bad inductor, they will fail again.

 

[rhempz01]

How do I determine which one is bad? Should they both have oscillation at pin marked output?
The amplifier does have audio.

 

[Perry Babin]

With the caps in place, you should have rail-rail oscillation on one terminal of each inductor and essentially nothing (but audio) on the other terminal.

If you connect a dummy load between the cap and inductor, you may be able to see far more noise on one inductor than on the other.

 

[rhempz01]

Do you know what they should measure by chance perry if I can get them out, they are proving most difficult to remove.

 

[Perry Babin]

Compare the readings in the board with the filter caps out of the circuit. If you remove them, you may break any intermittent short and they may appear to be OK.

You can also install the filter caps with a current limiting resistor in series with one terminal of the cap and compare the voltage across the limiter, one side to the other to see if they're the same.

 

[rhempz01]

OK I'll remove the filter caps and see what I have on both of them in curcuit.