full documentation of telequipm D61 scope (mine is D61a) see:http://www.hobbielektronika.hu/forum/getfile.php?id=262895

 

Hate to disapoint anyone who offered help. After doiing the measurement, I happen to have nothing anymore at all at my scope tube..as if it died

I'm not sure I follow? Do you mean that the display now remains dark? Did performance of a measurement precipitate said symptom? If so, what were the circumstances of the measurement/procedure?

I had no HV probe and made one with a serial R of 3,4M and between the measuring electrodes 340K

As I understand your description, said arrangement presents a resistance of ≈3.7MΩ to the circuit under test (i.e. 3.4MΩ+[10MΩ*340KΩ]/[10MΩ+340KΩ]) Please be advised that said impedance is rather low for 'flea power' 'EHT work' and will likely overload said circuits with consequent erroneously low readings... Consider, for instance, that the measured value of 1730V (above) represents a current of >460uA!!!

any ideas on what to check next?

Absolutely! I will carefully examine your readings and get back to you early Thu AM (Note: I reside in the UTC -6 timezone)

Best regards
HP

 

I'm not sure I follow? Do you mean that the display now remains dark? Did performance of a measurement precipitate said symptom? If so, what were the circumstances of the measurement/procedure?

As I understand your description, said arrangement presents a resistance of ≈3.7MΩ to the circuit under test (i.e. 3.4MΩ+[10MΩ*340KΩ]/[10MΩ+340KΩ]) Please be advised that said impedance is rather low for 'flea power' 'EHT work' and will likely overload said circuits with consequent erroneously low readings... Consider, for instance, that the measured value of 1730V (above) represents a current of >460uA!!!
HP

Indeed 3.4MΩ in serial with testpin and 340K between 2 electrodes could influence the measuring.
What would you advise for both probe resistances? ten times more for both?
Discovering the fact that I saw nothing anymore on the tube was before any in circuit measurement. I desoldered R68 and the -13V at R69 in order to check resistors. Everything was OK exept that R69 potmeter appears to be 36K instead of 22K, but I guess this is far from critical. After soldering every thing back I was astonished to see nothing any more at the tube screen. I have double checked all solderings and wirings around the work area. All seems OK. I rechecked TR33 and 37; are bothe OK; also checked TR31: OK; It is only afterward that I constructed the probe. Since tensions are present, I suspect sweep generator, but I do not know how to manage without a scope. Thanks for all yr efforts.

 

as you might have suspected i am in UTC +1. Have a good night!

 

What would you advise for both probe resistances? ten times more for both?

EHT probes applicable to service of low current equipment are typically designed such that the instrument reading corresponds to 1/100th the measured value -- hence, equipped with such a probe, a 10MΩ DMM requires a 1GΩ divider resistor... Thus the current at full scale (typically Speced at 50kV) ≈49.5uA --- If not in possession of same, please be advised that such resistors are both difficult to source and rather delicate -- my suggestion is that you arrange the highest impedance 'probe' practical and anticipate (i.e. 'allow for') loading of low current supplies... Note that focus divider resistors may be useful in this regard -- One caveat: construction technique preclusive of flashover is imperative!

After rectif; 9) 111 V; and 10) -12,8;

Good and good!

Based upon this resource: 1324Y/1346Y Data
heater: 6V AC → Ok
cathode part of heater at -810 (intensity low); -560V (intensity high) → Without regard to the appropriacy of the readings - pins 2 & 3 should be at very nearly the same potential with respect to the chassis...

on g1(intensity): -620;
on a2 (focus):-510 ->-700; on A4(anode?) +1730V (should be 2500);
on g of GEOM:+50;

We'll leave analysis of these reading in abeyance pending correction of the 'blank display' issue


On the face of it, there are but three 'problem categories' that may result in a wholly dark display:
1) A 'gassy' or otherwise defective CRT (Not likely unless the tube experienced physical 'trauma' in the interim).

2) Electrode EMFs inconsistent with beam current (e.g. 'faulty' bias, accelerating potentials, etc...) -- (In consideration of the probe impedance, I regard the a4 EMF reading to be acceptable -- in any event it is sufficient to produce light on the display...)

3) Deflection electrode differential EMFs inconsistent with an 'on screen' display

I desoldered R68 and the -13V at R69 in order to check resistors. Everything was OK exept that R69 potmeter appears to be 36K instead of 22K, but I guess this is far from critical. After soldering every thing back I was astonished to see nothing any more at the tube screen.

Given that the difficulty occurred following your inspection of R68 and R69 (both being central to the horizontal deflection circuity) -- it seems 'etiology #3' (above) is likely...

R69 potmeter appears to be 36K instead of 22K, but I guess this is far from critical.

Perhaps not critical per se - howbeit a ≈ 163% discrepancy is significant - and may well be syndromic with further problems in the potentiometer (e.g. dropouts secondary to compromised wiper contact, etc...) -- Please check the pot for tracking (First from one 'end' then the other) with an analog resistance indicator -- Or, better yet, temporary install another pot (Nominal resistance within 20%) then attempt to adjust for a display...

Please keep us posted! -- You've got my word that we'll return the scope to full working order - or know the reason why not!

Best regards
HP

 

EHT probes applicable to service of low current equipment are typically designed such that the instrument reading corresponds to 1/100th the measured value -- hence, equipped with such a probe, a 10MΩ DMM requires a 1GΩ divider resistor... Thus the current at full scale (typically Speced at 50kV) ≈49.5uA --- If not in possession of same, please be advised that such resistors are both difficult to source and rather delicate -- my suggestion is that you arrange the highest impedance 'probe' practical and anticipate (i.e. 'allow for') loading of low current supplies... Note that focus divider resistors may be useful in this regard -- One caveat: construction technique preclusive of flashover is imperative!


Good and good!

Based upon this resource: 1324Y/1346Y Data
heater: 6V AC → Ok
cathode part of heater at -810 (intensity low); -560V (intensity high) → Without regard to the appropriacy of the readings - pins 2 & 3 should be at very nearly the same potential with respect to the chassis...


We'll leave analysis of these reading in abeyance pending correction of the 'blank display' issue


On the face of it, there are but three 'problem categories' that may result in a wholly dark display:
1) A 'gassy' or otherwise defective CRT (Not likely unless the tube experienced physical 'trauma' in the interim).

2) Electrode EMFs inconsistent with beam current (e.g. 'faulty' bias, accelerating potentials, etc...) -- (In consideration of the probe impedance, I regard the a4 EMF reading to be acceptable -- in any event it is sufficient to produce light on the display...)


3) Deflection electrode differential EMFs inconsistent with an 'on screen' display

1/ No trauma's in anamnesis (far or recent)
2/ ok acceptable i understand
3/I changed the potmetre with one of 22K: makes no difference
K.reg

 

[
I measured at middle of the temporary 22K potm R68 in utmost right pos: -12.1V; at "-13V point" I measure -12.2V;
at the "156/59 ref": -1.04V(DC)

 

Dont have an anolog meter, but I suppose I would see an interruption... in the case I see something on the tube...Thanks for encouragements. Start to need it...

 

I measured at middle of the temporary 22K potm R68 in utmost right pos: -12.1V; at "-13V point" I measure -12.2V;
at the "156/59 ref": -1.04V(DC)

R68 does not appear to be a potentiometer?
I doubt R68 is the problem -- please substitute R69 with another potentiometer, then see if you can get a pattern on the tube... If you cannot obtain a pattern following substitution, please measure the EMF between the wiper and ground at R69 shaft positions of: full CCW, full CW and mid-range...

For my convenience please tabulate the readings as follows:

R69:
Full CW = __
Full CCW = __
Mid = __

Best regards
HP

 

Dont have an anolog meter, but I suppose I would see an interruption... in the case I see something on the tube...Thanks for encouragements. Start to need it...

Don't worry about it! -- The method outlined in post #69 will be just fine!

 

R68 does not appear to be a potentiometer?
I doubt R68 is the problem -- please substitute R69 with another potentiometer, then see if you can get a pattern on the tube... If you cannot obtain a pattern following substitution, please measure the EMF between the wiper and ground at R69 shaft positions of: full CCW, full CW and mid-range...

For my convenience please tabulate the readings as follows:

R69:
Full CW = __
Full CCW = __
Mid = __

Best regards
HP

HP I say it is typo! I say he means R69 cuz he's talking about pot! I like idea to tabulate cuz numbers separated by semicolon too confusing. Good luck!

 

Thanks for encouragements. Start to need it...

No worries!!! -- We'll get it sorted!

 

HP I say it is typo! I say he means R69 cuz he's talking about pot!

Hey Aleph!

Very likely -- howbeit it pays to be certain!

Al the best
HP

 

indeed I changed R69 by a potm of 22K, (sorry for the typo): The measurements below are done on the old (36KOhm) one since I took the temporary 22KOhm potm. away since it didn't helped.
Full CW = 0 V
Full CCW = -12.2
Mid = 4.1
k.reg

 

Please read MID=-4.1 !

 

indeed I changed R69 by a potm of 22K, (sorry for the typo): The measurements below are done on the old (36KOhm) one since I took the temporary 22KOhm potm. away since it didn't helped.
Full CW = 0 V
Full CCW = -12.2
Mid = 4.1
k.reg

Understood that Mid = -4.1

That's probably as should be considering the loading on the wiper -- are you certain that R66 is ok?

Did you turn the replacement pot through its entire range while watching the display? -- If yes, are you certain all other controls were set so as to allow a display?

Please tell me everything you did with the Scope between the last time the display showed a pattern and your initial discovery that it was blank...

Best regards
HP

 

Yes I checked R66 it was 17.9K; The only thing I did was desoldering R66 and the wiper leg andt the -13V conn. of the R69. What do you think of the 12V AC on my soldering iron...
and Yes I always check buttons or switches: Intensity; focus ; TV/A and +/- switches and vert positions of channels and X5/X1.

 

I ment TV/AC

 

What do you think of the 12V AC on my soldering iron...

Is the soldering iron grounded? If not it's probably down to a low current element-to-tip fault in the soldering iron -- I strongly suggesting grounding the tip - for both electrical safety and protection of equipment!

But first - To make certain it is the iron and not the scope chassis that's 'elevated' - please check for EMF between the iron's tip and the mains receptacle ground...

Let me know what you discover

 

Is the soldering iron grounded? If not it's probably down to a low current element-to-tip fault in the soldering iron -- I strongly suggesting grounding the tip - for both electrical safety and protection of equipment!

But first - To make certain it is the iron and not the scope chassis that's 'elevated' - please check for EMF between the iron's tip and the mains receptacle ground...

Let me know what you discover

Mains ground is connected to frame at scope interior. I must admit that in this 1800 century house I haven't check ground quality since I dont have a megger. I 'll ground the iron for next soldering actions.