Re: 7854 Repair & Restoration

Brian Bloom

I am going to try to get this U50/vertical amplifier issue figured out & resolved this weekend.
I've had to set the project aside for the week while I fix, clean up, calibrate, and list at least one of the 485's so I can get some more project funds flowing in.

I'm hopeful that It'll be a simple fix and not a U50 failure! If I'm stuck replacing U50, I'd like to just replace the entire vertical amp board for the time being while I obtain the proper equipment to re-adjust the affected circuitry. I'd prefer not to have to make one scope from two, though.

Good news regarding my newly acquired 7S14:

Only one of the four Hg cells in my 7S14 is bad. The other 3 measure near 1.36V. They are Duracell D313. All look to be in good physical condition with no leaks, rust, etc. So at least 1 channel will likely be functional.
I'll clean it up and test it out sometime this weekend, hopefully.

I'm wondering how I should proceed with this. I don't want to replace the good ones.

I can find similar 1.35V mercury coin cells ( PX625 ), but not exact replacements. Does anyone see any reason why I couldn't just use one of those? I wouldn't be willing to weld/solder tabs into the cell itself, so I would probably use a couple pieces of balsa and a small zip tie to secure it between the old cell's contacts.

Once the old Hg cells do fail, I think I may go the 'battery' route, whether it be with two individuals or a single 3V coin cell and a voltage divider arrangement. Doing so would add some more info to the wiki for that solution.

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