If there's soot on the pot you are advised to check it's resistance and wiper connection integrity...

Have juist looked with magif.glass. Coal deposition seems to be coming from small bulging in C645 just near it. (Y amplifier)

 

Have juist looked with magif.glass. Coal deposition seems to be coming from small bulging in C645 just near it. (Y amplifier)

Please give me a moment to find it on the schematic

 

Please check R104 and R98 out of circuit -- make sure R104's wiper maintains proper 'connection' to each 'end' throughout its travel...

i ll desolder R104 and check it. Will be tomorrow since I have to go shopping.
CU later and many thanks

 

Good enough! --- In the meantime I'll make a step-by-step troubleshooting list - and post it sometime tomorrow!

OBTW -- If C645 shorted, it would likely load down the 13V rail -- If it is indeed ruptured - then by all means replace it! - though I doubt it is the cause of your Horz. difficulties...

 

Have desoldered R104: is 280 instead of 220 ohm; turning it degaged coal dust. Guess that's the one. Unfortunatly I dont have a spare. 'll have to order one. (Can be few weeks ...). I 'll keep U updated. Many thanks for yr fantastic help. Hypatia should be your protégé.

 

Have desoldered R104: is 280 instead of 220 ohm; turning it degaged coal dust. Guess that's the one. Unfortunatly I dont have a spare. 'll have to order one. (Can be few weeks ...). I 'll keep U updated. Many thanks for yr fantastic help. Hypatia should be your protégé.

@patpin
Inasmuch as R104 is connected as a rheostat, you may temporally use a 1K pot in its place to continue troubleshooting -- Just make sure to adjust it such that no more than 220Ω appears between the wiper and R98



Best regards
HP

 

I have found a 220 ohm in another device and replaced the presumed bad one on the scope... no cure yet...

 

I rechecked supply voltages: test point 205/18 appears to be a little low (-12.66V (should be -13 V);
at R69 top -12.33 (expected -13V)
checked on trafo: 13V AC is not present either: it is 12.2VAC; (previous checks were 13V)(I checked with 2 DMM's)
the 100V point is only 93V (OK before)
The primary voltages are OK (mains 234V;trafo not hot; no noise); C 402/403/408 not hot or bulging or leaking

 

I have found a 220 ohm in another device and replaced the presumed bad one on the scope

Good deal -- Please set it to ≈ 100Ω (Wiper to 'R98 end") and we'll continue trouble shooting!

 

I rechecked supply voltages: test point 205/18 appears to be a little low (-12.66V (should be -13 V);
at R69 top -12.33 (expected -13V)
checked on trafo: 13V AC is not present either: it is 12.2VAC; (previous checks were 13V)(I checked with 2 DMM's)
the 100V point is only 93V (OK before)

I don't make much of that so long as the transformer is not overheating or (audibly) noisy...

 

@patpin

That facts that horizontal deflection is linear but either insufficient or unbalanced -- taken with the observation that deflection is occasionally normal (during a portion of the warm-up period) tends to implicate the horizontal (X-Axis) driver circuitry (specifically, an intermittent condition therein)...

So, to the 'prime suspects'...

-Please check the decoupling resistor R124 for correct resistance (5.6K)
-Please check the decoupling capacitor C56 for a shorted or otherwise electrically leaky condition (Replace for any reading < 100KΩ) -- Note - a momentary 'down scale' reading following connection of the meter is normal...

Note: The above tests must be preformed 'out of circuit' (i.e. with at least one lead disconnected from the circuit)

Please remember to disconnect the scope from the mains prior to desoldering/soldering!!!


Let me know what you find!

Best regards
HP

 

Hallo, R124 is 5.48K; I cannot measure on C56 since I ll have to remove the whole time/div block. Are there other suspects we can check first.
Exteriorly C56 is in good shape( for what thats worth).

 

Dont understand that part of the diagram either. Fig 3; on top; Point 205/15 bringing 110V and after R124 (left of it) stil remaining 110V...no current through it?

 

Dont understand that part of the diagram either. Fig 3; on top; Point 205/15 bringing 110V

110V is applied to the horizontal amplifier at point 156/29, whence it is connected to the horizontal driver (and other circuitry) via the decoupling network (R124 and C56) -- (Where are you seeing point 205/15 ???)

and after R124 (left of it) stil remaining 110V...no current through it?

The EMF drop across R124 will be slight for the following reasons:
1) The current demand of circuitry left of R124 (as per the schematic) is relatively modest.
2) Inasmuch as said demand is undular, C56 functions much as a filter (a.k.a. 'smoothing') capacitor..

Best regards
HP

 

110V is applied to the horizontal amplifier at point 156/29, when it is connected to the horizontal driver (and other circuitry) via the decoupling network (R124 and C56) -- (Where are you seeing point 205/15 ???)



The EMF drop across R124 will be slight for the following reasons:
1) The current demand of circuitry left of R124 (as per the schematic) is relatively modest.
2) Inasmuch as said demand is undular, C56 functions much as a filter (a.k.a. 'smoothing') capacitor..

Best regards
HP

 

Hallo, R124 is 5.48K

Good...

I cannot measure on C56 since I ll have to remove the whole time/div block. Are there other suspects we can check first.
Exteriorly C56 is in good shape( for what thats worth).

Yes, please check the EMF across C56 (i.e. the 'left side' of R124 to the chassis) --- Please connect your indicator such that you may observe any EMF changes during the entire warm-up process until symptoms of 'full' malfunction appear)

Please be advised that there are many other 'things' to examine/inspect -- howbeit I prefer a 'first things first' approach

Talk to you later!
HP

 

@patpin

You don't seem to have included a message on post #155?

 

Our diagrams are apparently slightly different. I see 110V at top Right and top left. In one of my first fig 3's the left side was cut off.

 

@patpin

You don't seem to have included a message on post #155?

It was erraticly posted. Sorry

 

Our diagrams are apparently slightly different. I see 110V at top Right and top left. In one of my first fig 3's the left side was cut off.
View attachment 98894

I'm using the schematic for your scope (D61A) -- anyway there is no real difference -- the drop will be negligible for reasons summarized in post #154