Fried CR-620?

andykill

New Member
Hello all! I need some help figuring out how to resuscitate a CR-620.

The problem:
When the unit powers on, the red LED light for AM/FM comes on but the relay does not click out of protection.

The symptoms:
I opened it up and found some of the transistors and the variable resistor have a blue-green residue on them. Also, the plastic tube containing some leads has been burned. There are four ceramic looking resistors and a braided fabric covering another component beneath the plastic tube.

The parts that look fried: TR709, 710,713,717,718, 719, 720, 721.

I am a bit of a noob to electronics but I know enough to get in trouble :D

Can anyone make sense of this? Any help is much appreciated. Please be a detailed as possible and dumb it down for me. Thanks!
 
Pictures

Here are some pictures of the carnage.
16417732668_c6b33a1343_c.jpg


This is the burned tube. Underneath the burned part is a fabric covered part next to 4 ceramic resistors.

16603765231_10763b7364_c.jpg


This is a shot of the part of the board with the transistors that look fried. Any ideas what would cause this? I really need help.
 
Last edited:
I can only see the first image, but from the looks of that trimpot I wonder if something got spilled in it. When things are burned up you've got some major troubleshooting ahead of you. Typically one pulls the obviously bad parts, uses a DVM on "diode" range to check diodes and transistors, checks the resistance of associated resistors and looks at the schematic asking "where did the excessive current flow and why?" A good check-out of the power supply is always needed as well. Where are you?
 
what caused it ? do you remember or is it new to you ?
quick look and seems to have been over-driven somehow . maybe massive feedback or a power supply fault . damage in both channels mainly at input stage of main amp .
 
I fixed the picture. I haven't gotten anywhere close to pinpointing the problem. It was given to me by a friend and I am trying to see if I can fix it or to just junk it. I have a DVM. What am I looking for when testing? It's not a very expensive one so I may be limited as to what I can do. Please advise. Thanks!
 
that's had liquid spilled in there .. the trimpot has gone bad and shorted or open and sent the bias crazy .
you need to replace all the trimmers for sure .
all transistors resistors and diodes need testing . including the outputs .
power supply needs checking too .
might not be too costly . . could take a while though .
another way is replace all transistors and diodes and trimpots and checking resistors replacing bad ones .
 
Back
Top Bottom