8080 Need Advice

[Mototo]

First off thanks to everyone who chimed in on my last thread. I couldn't have fixed that unit without all your help.

I'm hoping to get some guidance on a new project. I have an 8080 that picked up on Craigslist. It's in pretty rough shape but I have it partially working. When I got it, it was missing the rear fuse cap and most of the fuses in the unit were the wrong values, and most were blown. I sourced a replacement fuse cap and replaced the fuses, along with the two fuses on the driver board that appears to be post fuse notice. I checked the fusible resistor values on the driver board and everything is close enough to in spec, but will eventually be replaced. After connecting my dim bulb tester I powered on the unit and everything looked good. I removed the DBT and biased the unit. I also checked the channel voltage while I was at it. I have deoxed all the switches and pots multiple times. I have one channel, the right channel, I just can't seem to get working regardless of input or switch selection. I have poked and prodded the switches, relay, and boards to see if I get any change but nothing so far. If I connect a phone to the main in I get audio out of both channels. If I remove the pre out main in jumpers, and use rca cables to rotate the jumper in the problem moves between channels.

Any help would be greatly appreciated.

Thanks
Mototo

 

[LBPete]

If it moves from one channel to the other when you cross connect the pre out, the problem is in the preamp. Do you get both channels when you push the mono switch? If so, the dropout is in the signal path before the mono switch.

Can you post the serial number for the database? Click on the link below.

- Pete

 

[Mototo]

Pete,

Thanks for the reply. Moving the switch to mono or stero still only results in one channel.

I didn't see a link in your last post. Would you mind posting it again, or I'll message you directly with the serial tomorrow?

Thanks,
Mototo

 

[LBPete]

The link is in all of my posts. Look below. If it doesn't produce sound with the mono switch, the problem may be on the output side. Check the speaker switch. To narrow it down more, pull the U jumpers out of the pre out on the back of the unit. Use an RCA cable to connect the left pre out to the right main in and the right out to the left in. Does the channel drop switch sides? If it stays on the same side, the dropout is in the amp section. If it switchs sides, it's in the preamp between the mono switch and the pre out.

- Pete

 

[Mototo]

Pete,

Sorry for the several month delay on this. I ended up tracing my issue to a bad ba312 ic. The unit still needs some work but progress is being made... finally

Thanks