REVOX B780 does not retain tuner preset memory when unplugged

[Boogeydog]

Good Day All,

Hoping for some great guidance. I recently rebuilt a Revox B780 that was for the most part still working except for two issues. One was one phono channel was dead, the other tuner memory was not being retained when unplugged. Replaced the electrolytics, cleaned IC sockets and all connectors, replaced some badly corroded IC's yada yada. Got everything working pretty good but no luck with memory issue. I did have to clean the battery compartment and connecting wires. Checked that there is proper voltage leaving the battery pack. Checked that a charge voltage was present for the battery pack. My suspicion, being that I had badly corroded IC's, the one responsible for retaining memory requirers attention. Tracing to this extent is beyond my capability however. I would like to get it working 100% as it is a wonder of design. Any suggestions would be greatly appreciated!

Many thanks!

[wasedadoc]

What are the battery voltages when the tuner is plugged into AC and when it is not?

[GLouie]

I don't know this unit, but a quick scan of the service manual from HiFi Engine indicates you need to check for battery pack voltage at pin 4 of the microcomputer chip IC1, which looks like memory backup.

[Boogeydog]

Somewhere around 5.6 both ways.

[Boogeydog]

Thanks for that. It is looking like trouble with the microprocessor. I think I am boned.

[wasedadoc]

How long between removing power and measuring the voltage? How long does the power interruption need to be for memory to be lost?