Kenwood 700m repair help

[pcimone]

Ok, so I have two kenwood 700m amplifiers and both are having the act same problem after I recapped them.

The first one I went all in and replaced everything. As soon as I power it up, it cooks the large white ceramic resistor mounted to the inside of the rear panel.

So I buy another one and figure I'll go slow, one part at a time. So I start by just replacing the two main filter caps. Power it up, exact same problem. Put the old ones back, still doing it.

I need help. I don't see any shorting cables or anything. I barely did any work to the second one and it's just strange that both are doing the exact same thing. When this happens, the relays do not activate. It just immediately smokes that resistor.

Thanks in advance. I'm now thousands of dollars into this and I just want a working amp.

 

[cademan]

It's possible that you accidentally connected an electrolytic backwards. Once done, a part has already been damaged.

Look at any transistors associated with that resistor.

Study a schematic and make sure the replacement capacitors are connected with the proper polarity.

Some designs use a pair of capacitors in a series connection where one capacitors negative will be connected to the other capacitors positive. Some designs strictly use all capacitors in parallel depending on capacitance needed for that circuit and design. Some designs use normal connections where negative is the same as chassis ground.

Have you got a schematic and/or pics?

 

[pcimone]

It's possible that you accidentally connected an electrolytic backwards. Once done, a part has already been damaged.

Look at any transistors associated with that resistor.

Study a schematic and make sure the replacement capacitors are connected with the proper polarity.

Some designs use a pair of capacitors in a series connection where one capacitors negative will be connected to the other capacitors positive. Some designs strictly use all capacitors in parallel depending on capacitance needed for that circuit and design. Some designs use normal connections where negative is the same as chassis ground.

Have you got a schematic and/or pics?

So, it was only the two main filter caps and I'm 100% sure they are in correctly. It makes no sense. Literally opened the unit, undid the 4 bolts on the top of the two filter caps, installed two new ones of exactly the same value. Smokes soft start resistor now. Both units, same exact symptom.

 

[painttoad]

were they working before you started replacing parts?

you should build a dim bulb tester and you will likely need a 150watt bulb for this amp.

since you say that the relays don't close, the unit should still power up and possibly even run thru the softstart resistor without smoking so i would be looking at shorted output transistors.

you need a dim bulb tester before you do anything else. lots of threads on here, use the search feature