CR-2020 mess.

I am working on a CR-2020 for an AK'er. He got it from a local repair shop that no longer services vintage gear. Any way, it is pretty butchered.

The regulators were replaced, and in doing so, the traces got trashed and jumpers and solder were installed to complete the circuits.

The transistors they used are 2SD1276A and 2SD1267A. I think they meant to install 2 1267s, but they failed. What do you think of these?

Maybe these would work, but the voltages are all screwed up.

The receiver wont come out of protection, but I can force it to by shorting the relay driver. I only did this for a second. I thought it would be a transistor or cap in the protection circuit, so I replaced about 4 caps and 4 transistors. Didn't help.

The power supply board was about 50% recapped by the previous shop.

There is less than 30mv of DC on the amps outputs.

I will replace the regulators, but it will be a pain since the traces are gone.

Rob

If you need any photos let me know. I have a 2020 opened up down in the shop.

Robbie
BTW there is a silkscreen cap polarity mistake on the electrolytic board.Maybe someone installed a cap ass backwards.

Photo of a incorrectly installed cap due to silkscreening ..
http://www.audiokarma.org/forums/showpost.php?p=4756787&postcount=2

avionic said:

If you need any photos let me know. I have a 2020 opened up down in the shop.

Click to expand...

Thanks.

I actually have mine open right now too.:yes:
It's on the back burner for the SB updates.

I'll check that cap as well, but I don't believe they changed any on that board. Although the one that's in the way was obviously hit over and over as they worked on this, because the traces are lifted and the cap moves around.

I will replace it and glue it down before returning it to the owner.

I did notice that the power supply board with the relay on it is different than the one in mine. It has at least one more cap on it. Didn't look much closer than that.

I think the transistors they installed for the regulators are causing problems.
The voltages on their pins are way different than on mine.

Rob

I replaced the regulators with what I had, TIP32AG's.

Now it comes out of protection and music plays.:yes:

But, there is a hum that changes with volume. I used a preamp and there is no hum.

So, do you think it could be the transistors I used for the regulators?

The hum is in both channels.

Edit: Did some searching and it seems that it could be caps for the 25 volt supply. Guess I need to replace them.

Second Edit: Replaced the 1000uf 50 volt caps and the hum is still there.

Rob