Jim Yanik wrote in message ...
(Holger Menges) wrote in
m:

Hello,

I've got a problem with my Tektronix scope 7313. After switching on I
hear a crackling from the inside (only for a short time, then the main
is melting).
Has anybody of you got a similar problem with a scope from the 7000
series?
Has anybody got spare parts for the scope?

Thanks,
Holger


This is a really old scope.
Do you have a service manual?
What do you mean by the "main" is -melting-?
Is the line fuse opening?
How are the low voltage supplies? In tolerance,low ripple?


Your scope probably has a HV problem.

Sounds like the main fuse blows or one of the fuses in the LV
supplies.

I'd recommend Holger gets himself a service manual. Best is one for
the 7313,. If a free download from www.logsa.army.mil (TM section,
tektronix ,lokk for a 7603 model) helps, this low voltage (LV) power
supply are quite similar.

To the fault description: Looks like one of the rectifiers (bridge
type) are malfunction (shiorted/partly shorted). Or one of the big
electrolytic capacitors is shorted (happens seldom, but happens).

As Jim proposed: Check the power supply voltages and the ripple FIRST
before going deeper in search. Use a variable AC transformer (german:
Stelltransformator; here we say variac) this eases repair a lot.

HV problem is possible, but this check comes after checking the LV
supplies.

hth,
Andreas