Machine in shed for 15yrs - 1/4" audio tape PR99 Revox

[carolmaille]

Hello again. I have recently collected some machines from a terrace shed. They are analogue audio. One is an oscilloscope. All seem to have lights on to begin with, but I just put them on for a few seconds. The Revox PR99 1/4" tape machine was once a good machine I bought it from a redundant plant:
On the back next to the socket I lowered the power to 140V from 220 and switched it on; the LED display came on the Record light came on - then it all went off: The fuse on the machine seems to have blown
So - would this be because something went short circuit after switching it on for so long ? Would it be a capacitor but that would go open circuit ? So do you have any ideas of why this happens or/and of how to proceed please ?
With the oscilloscope I read to switch it on progressively for longer times while leaving it for 30 min in between ? Many thanks for suggestions, Have a good day Carol

 

[alec_t]

Welcome to ETO!

On the back next to the socket I lowered the power to 140V from 220 and switched it on

The selector on the back doesn't 'lower the power'; it selects the appropriate input for the mains voltage. If you set the selector for 140V, that's what the mains voltage should be. So applying 220V mains with the selector on 140V will destroy something. If you're lucky, only the fuse has blown.

 

[carolmaille]

Oh good, so the circuit selected was expecting 140V and it got 220V yes of course that makes sense now, I don't have a variable input, it is for a machine in different countries. Yes hopefully it is just the fuse ! I will get another one and get back here. Thank you so much

 

[danadak]

Older instrumentation have bulk caps in them, electrolytics, that can degrade over time.
And many with tantalums that essentially become shorts. Dipped tants very much a
restoration project to replace.

"Normally" one brings up these older instruments with a variac over some time, ramping
V over hours, a day or two, sometimes avoids damage thru cap reforming.


Regards, Dana.

 

[carolmaille]

That's good to know maybe I need to borrow a Variac as I would like to try to avoid replacing the dipped tants if possible

 

[danadak]

The variac will not help with the dipped tant problem. Just the electrolytics.

As a rule of thumb one just simply replaces the dipped tants, they are notorious for
failing as dead shorts.

I restore 90's era Tek scopes, 30 - 50 of those dipped tants to replace, tedious
to say the least.

 

[carolmaille]

That's okay as long as the track can hold - I just don't have a solder iron here but I am sure I can get one easily enough. Do you order them from RS or Farnell or something? And just lead solder. I can try to download a manual tomorrow and order them - and the electrolytics I guess. I also have a scope it seems to be dead - the tube - I guess it could be more capacitors !