Technics SU 8080 Channel Imbalance Problem (Left Channel Is Quieter Than Right Channel)

[Ivan T]

I have the Technics SU 8080 integrated amp with a channel imbalance problem - left channel is quieter than right channel even if I run it in power amp mode. All electrolytics (except power supply ones) have been replaced with Panasonic FCs, FRs, Elna Silmic IIs and some Nichikons, depending on availability. One of power supply caps (C503 - left channel) drains much faster than the other ones when the amp is off. Any suggestions from the local community? Is this a common issue with this amp? Where should I look? Speaker relay, volume and/or balance pots, speaker selector (sounds a little "scratchy"), direct/via tone switch ( sounds a little "scratchy"), DC/low cut switch (sounds a little "scratchy"), power limiter boards, resistors? Please, help.

P.S. When I try to adjust power limiters according to the service manual - nothing happens to the waveform on the scope screen.

 

[Ivan T]

the protection circuit is across one of the capacitors, the 2 switches dc\ac couping and the other usually need ripping apart and contacts cleaning,
measure across the relay and check the resistance - never a bad idea to clean the contacts nowadays

Thanks for the advice. It's a good thing that the amp is still taken apart, because the protection board is very hard to get to once you put the amp back together. I'll try that tomorrow. Can you actually take the "DC/low cut" and "direct/via tone" switches apart to clean them? What exactly do I need to measure on the protection board? I can't seem to understand how to clean pots (e.g. volume and balance pot), because it looks like you can't take them apart to clean them.

 

[Ivan T]

if the amp is in bits then its easier to measure across the contacts of the relay, the switches will come apart but may be easier to soak them in sw cleaner
spray sw cleaner in the pots

Thanks. I will get to it.