TEK 7623A repair ? + other 7623A related questions

[Bernhard]

Hi,

bought a 7623A with two 7A26 and one 7B71 on a flea market for 35 EUR and as it was to expect for that price, the thing does not work.

My question is: What is wrong with it ?

The cooling fan works, but no beam and no LEDs, even the Power LED is off.

All fuses on the big PSU unit ok, except the "15/100" on the "regulator" board that is mounted on the back side of the scope and has this aluminium cover on it.
But that fuse was broken mechanical, one cap was loose.

Where do I have to search ? No burned resistors so far.

Any link to manual PDF ?



Other questions:

Is this scope good for audio ?

Does it take the audio analizer plugin 7L5 ?

It is a scope with storage screen, the screen seems to be smaller than some others.
Is there another mainfraim with bigger screen, that fits the 7L5 and my plugins ?


Thanks, Bernhard

 

[till]

some information:
http://www.caip.rutgers.edu/~kahrs/testeq/7000.html

http://www.helo.de/helo/museum/tek/7000/7000.htm

exept some special stuff for very fast scopes (1GHz or so) you can use every 7 series plugin in every mainframe.

There is a yoahho group for TEK scopes you may ask speacial questions, because there are some very skilled freaks.

 

[jackinnj]

a service manual is available

but it will cost you USD58 from www.w7fg.com Unfortunately there is a real false economy in some of the scopes -- but for EUR35 you can certainly sell the plug-ins on EBay for more than you paid for the mainframe plus plug-ins !

if you aren't nice to a 7XXX scope by allowing it sufficient ventilation, the power supply can go out -- these scopes are so inexpensive now that it is less expensive to purchase a used one from a good seller.

to ship a 7XXX series scope from the US to Continental Europe costs about $80.

 

[Bernhard]

It looks like some supply voltages are missing.


TO3 power transistors on reg board ok, (square form) bridge rectifier in PSU ok, what can it be ?

Are input voltages on the reg board missing or does the reg board shut off because there is a short somewhere in the scope ?

 

[Bernhard]

Fixed

First problem was that the 150mA fuse for the 130V rail was not
replaced because I did not have one.

I was afraid to damage something with a 6A fuse, later I just
measured the current and it was 40mA = ok.

Without the fuse the PSU shuts off...

Second problem...:

Then with the 6A fuse inside, I pulled the plugins one after another
and the scope started working.

So the PSU was shut off by a defective plugin.

Next I opened the plugin and put the short-find-beeper across one
orange drop tantalum and it was clear: Short on one 15V rail.

The second tantalum I soldered out, was the bad one.
Shorted @ 1.5ohms.

Now the plugin and the whole 35 €$ scope works just fine.

 

[Brian Donaldson]

Bravo.
Good show.
It's nice to see a nice peice of equipment that cost more than most new cars (new) continue to function.