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Dear all,
I was given a Tek 7904 which was left abandoned in a garage for decades.
The instrument internal boards, cables and hardware is literally covered by a layer of dust about 1mm thick.
What is the best/recommended way of cleaning?
What is the best way to clean the pcbs?
Most of them seem very easy to remove, if required…
Does it make any sense (in terms of work) to try to remove the main pcb?
There ate probably bad tants to be replaced there, but read some comments that is is a nightmare to try to do it.
Thank you in advance for all the help.
Roger

Roger, in addition to any other support provided, take lots of pictures to help you if you disassemble anything. Aslo be careful when pulling the harmonica connectors as they can be very fragile in older scopes.
Bob

Some connector colors are much more brittle than others, but I'm drawing a blank on the culprits.??
-Dave

blue, from what I've heard.? I'd also suspect red and tan.

Harvey

Rogerio,

The boards can be removed then cleaned with Dawn, on a brush then rinsed off with water. Let dry long enough. The other parts can also be done the same way. The front and other metal parts can be cleaned with ammonia and a brush then rinsed. I suggest cleaning the knobs individually. IPA on a rag to get off any sticker residue and any other dirt that other cleaning did not remove. It will be tedious yet worth it. Oil the set screws and shafts of controls. The CRT can be removed and cleaned. The main board in the back, can be cleaned with a brush and Dawn or water, depending upon the dirt type. The removable sides and bottom can be cleaned with soap/ammonia and a brush. Use 91% IPA and a small brush to clean the legs/pins of the solid state devices while moving them up and down in their sockets right after applying the IPA. Clean all controls and switches with contact cleaner or IPA then exercise. You will be glad to take the time to clean it after you see it cleaned then working. I have had electronics that was filthy then after cleaning, looked excellent to new. I never regretted the time and effort in cleaning. I let dry in the sun all day, if warm/hot or over a heat register overnight when in winter. A fan will speed up the drying, then heat of some kind will do the rest while you are sleeping or at work for the day. Cleaned, there will not be an odour when turned on due to heat heating up the dust and debris.

Mark

Thank you all for the replies.
After a closer look I am beginning to loose hope to fix this unit.
The unit is really beaten.
Someone has been here before, and disconnected all the cables, harmonica connectors, etc probably trying to isolate a shorted tantalum.
I have downloaded the SM from tekwiki and it seems that it shows where each cable connects with the PCB's.
Is there any known error about the cabling connections in the SM?

I still have some questions:

1- How to treat the Power Supply "cube"?
Is it safe to remove the boards from it to clean them? It seems safe to do it
Can I wash the remaining parts of the "cube" after removing the boards for cleaning?
Is it safe to spill water (or wash?) the HV components?

2- Since all the rf cables (the ones with the golden connectors) were removed from their sockets, most of them have the central pin (wire) oxidized.
Is it a good practice to sand and tin the central wire?
What is the best way to "fix" them?


3- Is it possible to remove the pushbuttons assemblies (A20 and A21) from the front panel for cleaning?
It seems that it is, if I remove the -Front Panel Interconnect Board. (A3).

What I used for my 7904 was just an old toothbrush. Cleans off most of the dust and gunk, but doesn't damage anything. If you want a deep clean, follow what the other people above me replied.

Also the blue connectors are just dust at this point. Blue flour held together only by age.

I was going to suggest noting the orientation of all the harmonica connectors, because there are a few cases across the entire product line where the connector isn't installed correctly (or the manual is wrong), but if the cables have been pulled, that's not going to help!
-Dave

Thank for the suggestion Dave.
Although the connectors have been pulled out, the cables are so “dried” and “hardend” that it is possible to figure out how they were once connected.
Most of them are just one inch apart from the boards.
Lets hope this scope was working when the connector have been pulled out….