(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.

--
Jim Yanik
jyanik-at-kua.net

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

Hello,

thanks for your help, I've got a Service Manual for the Scope. But now
I've got 2 new Problems:
- the line fuse was blown after a short time when I switched on the
scope. Which Units should I disconnect for the LV - Test?
- How should I test the HV - unit? It's installed behind a shield and
two other PCBs are mounted on the shield.

I also think the Problem is in the HV - section, because the crackling
came from this direction.

Greetings,
Holger

(Holger Menges) wrote in
om:

Hello,

thanks for your help, I've got a Service Manual for the Scope. But now
I've got 2 new Problems:
- the line fuse was blown after a short time when I switched on the
scope. Which Units should I disconnect for the LV - Test?
- How should I test the HV - unit? It's installed behind a shield and
two other PCBs are mounted on the shield.

I also think the Problem is in the HV - section, because the crackling
came from this direction.

Greetings,
Holger


IIRC,There's a fuse on the cap rectifier board(top board on the lower rear
module,above the pwr xfmr) that supplies -15 unreg to the HV. If the HV has
a problem,that should open.Ribbon cables to the Z-axis PCB can be pulled to
isolate the HV/Z-Axis from the LV supplies.Check the manual for the right
ones to pull.Then,IIRC,the cal procedure identifes the place to measure the
LV supplies.

The LV regulator board (top assy at rear)has to be connected to the
interface PCB(where the plug-ins connect) by 2 ribbon cables to maintain
sense feedback and decoupling.The LV reg can have cracked solder joints on
the studs for the TO-3 collector screws,causing LV problems.also,the 'IC'
on the LV reg PCB should have the socket removed and the 'IC'(5-xstr array)
soldered direct to the PCB.


Note,the circuit description is a great source of info for knowing how the
scope circuits work. Read it!!
--
Jim Yanik
jyanik-at-kua.net

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

Hello,

thanks for your help, I've got a Service Manual for the Scope. But now
I've got 2 new Problems:
- the line fuse was blown after a short time when I switched on the
scope. Which Units should I disconnect for the LV - Test?
- How should I test the HV - unit? It's installed behind a shield and
two other PCBs are mounted on the shield.

I also think the Problem is in the HV - section, because the crackling
came from this direction.

Greetings,
Holger


IIRC,There's a fuse on the cap rectifier board(top board on the lower rear
module,above the pwr xfmr) that supplies -15 unreg to the HV. If the HV has
a problem,that should open.Ribbon cables to the Z-axis PCB can be pulled to
isolate the HV/Z-Axis from the LV supplies.Check the manual for the right
ones to pull.Then,IIRC,the cal procedure identifes the place to measure the
LV supplies.

The LV regulator board (top assy at rear)has to be connected to the
interface PCB(where the plug-ins connect) by 2 ribbon cables to maintain
sense feedback and decoupling.The LV reg can have cracked solder joints on
the studs for the TO-3 collector screws,causing LV problems.also,the 'IC'
on the LV reg PCB should have the socket removed and the 'IC'(5-xstr array)
soldered direct to the PCB.


Note,the circuit description is a great source of info for knowing how the
scope circuits work. Read it!!

Holger,

I'd strongly recommend to follow Jim's proposal. Especially about the
circuit (schematics) and the theory (there is a description chapter in
the service manual, describing the LV supply)

And, try to use a variac to limit the input current (see postings
above).
If you can't get access to a variac, use a sries light bulb (details :
google, sam golwasser, repair faq...)

good luck!

Andreas