Date   

Re: 547 HV Transformer: Bill Schell rewind failed

Roy Thistle
 

On Wed, Mar 3, 2021 at 08:06 AM, Dave Wise wrote:


I used to think my Bill Schell transformer was wax-impregnated; now I don't. I
think it's epoxy
Hi Dave:
Sorry to hear about your trouble.
Perhaps you don't remember... because the last time you handled the transformer was when you installed it... but, how does one mistake wax for epoxy?... or vice versa.


Re: 547 HV Transformer: Bill Schell rewind failed

widgethunter
 

Talked to Bill Schell a couple of decades ago about taking over and buying his setup from him.Instead, I ended up contributing what I had learned to Chuck Harris' efforts.My recollection is that Bill did NOT use epoxy, but potted in straight beeswax.Chuck and I discussed this at length, considering beeswax vs paraffin.Chuck tested 10 mixtures and found best dimensional stability with a mixture of both.
I suspect incomplete impregnation or less than ideal coil pack resulting from his scatter winding method.Never heard of a Schell rewind failing until now.Bernie Schroder

-----Original Message-----
From: Dave Wise <david_wise@phoenix.com>
To: TekScopes@groups.io <TekScopes@groups.io>
Sent: Wed, Mar 3, 2021 8:06 am
Subject: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

In 2017, my 547 with Bill Schell HV transformer (installed around 2000) was working.  It has sat unused in a dry basement since then.

Today, in March 2021, that transformer exhibits the same thermal runaway symptom as the original Tek part.  (Fades out in ten minutes.)

Hours of warming have not restored it.  I don't think it will.  I used to think my Bill Schell transformer was wax-impregnated; now I don't.  I think it's epoxy, and like Tek's, it has gone bad.

I hope other Bill Schell customers can check in with their status.

I have an ace in the hole.  In my drawer is... a 2010 Chuck Harris rewind.  To ice the cake, it's the one Stan Griffiths was evaluating - he gave it to me after he was done with it.  I'll install it soon.

Dave Wise


Re: 3T77 tunnel diodes (again)

Albert Otten
 

In hindsight I realize that the waveform at TP121 will also depend on how fast the feedback will react on the new sample.
That's probably why TP121 waveforms for the S-1 and S-2 are shown separately in the calibration section.
Pff.. long ago that I did similar measurement in 3S76 and 3S1.

Albert

On Wed, Mar 3, 2021 at 02:04 PM, Albert Otten wrote:


Hi Charles,

It would be interesting to look at the S-1 (or S-2) output at pin 4.
Accessible at TP121 <1> of your 3S2. This happens to be also TP121 in the
7S11. You don't need a time base in the 561A.
At the first sample after a jump of your input signal the S-1 responds at the
full jump voltage. That is because the feed-back voltage stabilized at the
level before the jump (with input frequency up to 10 kHz or so). At the
following samples the response will be less and less.
The response at TP121 depends only on the behavior of the S-1 and the quality
of the strobe pulses from the 3S2.

I added 2 pictures to your 3S2 album. Note that triggering on the TP121 signal
is not that easy. You will probably see a mixture of of responses with
different amplitudes.

Albert


Re: 547 HV Transformer: Bill Schell rewind failed

Dave Wise
 

?Update.


I retract my doom and gloom. Further warming seems to be restoring it after all. I simply left the scope running, with the intensity control at a safe position. I don't have a visible trace yet but as time passes I have to advance the control less and less to get one.


This data point corroborates the theory of moisture-ingress or other reversible reaction.


I will report back later.


Dave Wise


Note: This 547 has the 6AU5 screen grid voltage limit mod.

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Dave Wise via groups.io <david_wise=phoenix.com@groups.io>
Sent: Wednesday, March 03, 2021 8:06 AM
To: TekScopes@groups.io
Subject: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

In 2017, my 547 with Bill Schell HV transformer (installed around 2000) was working. It has sat unused in a dry basement since then.

Today, in March 2021, that transformer exhibits the same thermal runaway symptom as the original Tek part. (Fades out in ten minutes.)

Hours of warming have not restored it. I don't think it will. I used to think my Bill Schell transformer was wax-impregnated; now I don't. I think it's epoxy, and like Tek's, it has gone bad.

I hope other Bill Schell customers can check in with their status.

I have an ace in the hole. In my drawer is... a 2010 Chuck Harris rewind. To ice the cake, it's the one Stan Griffiths was evaluating - he gave it to me after he was done with it. I'll install it soon.

Dave Wise


2467B with display anomalies

johnasolecki@...
 

My 2467B has developed several problems with the display; I'm not sure if they're related or not but they started about the same time.

The first is if I put a sine wave on the screen and center it, it shows considerable distortion. If I move it well above or just below the center line it displays clean.
Secondly, as soon as a signal is applied the upper and lower readout will oscillate like a sine wave is passing through them. Still readable but definitely not proper.

It's my favorite scope; I'd be grateful for any suggestions on where to start looking.

John


Re: [Tek 485] No intensity control

marcosjl31@...
 

On Wed, Mar 3, 2021 at 07:00 AM, Ozan wrote:
Are you still seeing ~ -61mV as before at collector of Q1548 with no dot on
the screen? With no dot on the screen base of Q1544 should be closer to 6V. If
base is still at ~1V please check R1536 for drift to >2.2M, CR1539 for leaky
diode, Q1544 for low hFE.
I see ~42mV at collector of Q1548, no dot on screen in XY Mode.
Base of Q1544 is at ~1V, HFE measured with a TC1 tester : 214
CR1539 is ok : ~.6V and 0L
R1536 measured in circuit gives : 300kohm and 100kohm (when inverting the test leads of DMM).


Re: TDS3064B "ripple" on calibrator signal

Dave Peterson
 

David,

In my limited experience, I have seen this behavior before, but it's always been due to probe issues. Usually with a long ground lead. Readjusting the probe and ground for better connections at both ends has solved it for me. Hopefully that's all it is in your case. And sorry I don't have a better answer.

Dave

On Wednesday, March 3, 2021, 05:57:33 AM PST, David C. Partridge <david.partridge@perdrix.co.uk> wrote:

Running an up-hacked TDS3014B, and am seeing small amount of what I'll call
"ripple" on the top of the calibrator signal (i.e. the 5V part of the signal
- the 0V end is relatively stable by comparison).  By "ripple" I mean it's
dancing up and down quite slowly (2Hz?) by about 1/2 a trace width, and the
Ch1 Max value switches between 5.16V and 5.20V.

Has anyone here seen this sort of behaviour before?

Thanks
David


547 HV Transformer: Bill Schell rewind failed

Dave Wise
 

In 2017, my 547 with Bill Schell HV transformer (installed around 2000) was working. It has sat unused in a dry basement since then.

Today, in March 2021, that transformer exhibits the same thermal runaway symptom as the original Tek part. (Fades out in ten minutes.)

Hours of warming have not restored it. I don't think it will. I used to think my Bill Schell transformer was wax-impregnated; now I don't. I think it's epoxy, and like Tek's, it has gone bad.

I hope other Bill Schell customers can check in with their status.

I have an ace in the hole. In my drawer is... a 2010 Chuck Harris rewind. To ice the cake, it's the one Stan Griffiths was evaluating - he gave it to me after he was done with it. I'll install it soon.

Dave Wise


Re: International Orders for Peter Keller's book were MAILED TODAY

Paul Humel
 

I'm a newbie who joined this group recently and discovered the overwhelming
interest in Peter Keller's book. I'm curious about what appears to be the
"bible" of CRTs, but I missed the boat on ordering.



So I logged on to my local public library branch and was able to request a
copy from the UC San Diego Library. I suggest that if others would like to
"try before you buy" you might consider heading to your local library to see
if they can find a copy for you.



Paul Humel


Re: [Tek 485] No intensity control

Ozan
 


I used - as someone (Mark ?) suggested - 1N4937.
Looks OK. I will let DC restorer experts to chime in.


Are you still seeing ~ -61mV as before at collector of Q1548 with no dot on
the screen? With no dot on the screen base of Q1544 should be closer to 6V.
If
base is still at ~1V please check R1536 for drift to >2.2M, CR1539 for leaky
diode, Q1544 for low hFE.
Will check later on this afternoon and keep you posted. I guess it makes no
sense to check R1536 in circuit ?

Jose
This check is only needed if you are seeing ~1V instead of ~6V at the base of Q1544 with no beam. You need to lift one leg of R1536 to measure, 2.2M will be swamped out with any other connection.

With no beam R1536 should be able to pull base of Q1544 but it only supplies few uA so a small leakage at base node is all it takes to turn off the beam. It could be any of the components at base node of Q1544 (even Q1544 itself).

Outside XY or slow timebase modes R1534 is providing extra current.

Ozan


Re: [Tek 485] No intensity control

marcosjl31@...
 

On Wed, Mar 3, 2021 at 07:00 AM, Ozan wrote:

On DC RESTORER side : I changed all the diodes that are in the High Voltage
Please see Tom's message for another DC restorer issue, these diodes need to
have fast reverse recovery time in case you used a different diode than the
original.
I used - as someone (Mark ?) suggested - 1N4937.

for Time Div <20ms. For 50ms, .5s, .2s and .1s as well as the X-Y mode I do
not even get a trace ! (and that's new).
Is it new meaning it happened last few days, or new meaning that new for this
scope from the beginning?
It happened a few days ago.

I do not see any dot when in X-Y mode or in lowest Time/div positions =>
This
seems to point out something wrong elsewhere.
Are you still seeing ~ -61mV as before at collector of Q1548 with no dot on
the screen? With no dot on the screen base of Q1544 should be closer to 6V. If
base is still at ~1V please check R1536 for drift to >2.2M, CR1539 for leaky
diode, Q1544 for low hFE.
Will check later on this afternoon and keep you posted. I guess it makes no sense to check R1536 in circuit ?

Jose


Re: [Tek 485] No intensity control

Ozan
 

On DC RESTORER side : I changed all the diodes that are in the High Voltage
Please see Tom's message for another DC restorer issue, these diodes need to have fast reverse recovery time in case you used a different diode than the original.

for Time Div <20ms. For 50ms, .5s, .2s and .1s as well as the X-Y mode I do
not even get a trace ! (and that's new).
Is it new meaning it happened last few days, or new meaning that new for this scope from the beginning?

I do not see any dot when in X-Y mode or in lowest Time/div positions => This
seems to point out something wrong elsewhere.
Are you still seeing ~ -61mV as before at collector of Q1548 with no dot on the screen? With no dot on the screen base of Q1544 should be closer to 6V. If base is still at ~1V please check R1536 for drift to >2.2M, CR1539 for leaky diode, Q1544 for low hFE.

Ozan


Re: 7104 out of focus/astigmatism

 

On Wed, Mar 3, 2021 at 03:34 PM, Francesco Franzini wrote:


On my previous post i reported about the strange ripple on TP1784, i found the
the same on the "working board" from the other 7104, this trigger me thinking
about leakage on HV connection.
How about checking the 25 kHz 54V signal coming onto the HV board via P40?
There's a (remote) possibility that an unintended load caused by a problem on the rectifier board causes the unregulated voltage to drop enough to cause your problem on the HV board but not enough to seriously affect the regulated voltages (+/- 17V, +/- 54V, 105V). It all depends on the regulation ranges, of course.

Raymond


Re: 7104 out of focus/astigmatism

Francesco Franzini
 

On Wed, Mar 3, 2021 at 06:26 AM, Raymond Domp Frank wrote:


Francesco,
I realize now that you mentioned the replacement of several boards.

On Wed, Mar 3, 2021 at 02:59 PM, Francesco Franzini wrote:


Raymond, i am curious on the meaning to "tilt the scope" can you please
elaborate on that ?

I thought of the possibility of a gravity-sensitive problem, like an
intermittent in the CRT (hopefully not) and meant to temporarily change the
orientation of the 'scope by lifting its front, putting it on its side etc.

Raymond
I will get back with the result of this test and the reports on other test that i am going to do !!

On my previous post i reported about the strange ripple on TP1784, i found the the same on the "working board" from the other 7104, this trigger me thinking about leakage on HV connection.

Thank you
Francesco


Re: 7104 out of focus/astigmatism

 

Francesco,
I realize now that you mentioned the replacement of several boards.

On Wed, Mar 3, 2021 at 02:59 PM, Francesco Franzini wrote:


Raymond, i am curious on the meaning to "tilt the scope" can you please
elaborate on that ?

I thought of the possibility of a gravity-sensitive problem, like an intermittent in the CRT (hopefully not) and meant to temporarily change the orientation of the 'scope by lifting its front, putting it on its side etc.

Raymond


Re: 7104 out of focus/astigmatism

 

On Thu, Feb 11, 2021 at 07:25 PM, Francesco Franzini wrote:


and at any point of this "process" working with focus and astigmatism setting
i am able to have perfect trace and readout.

I guess you checked whether very carefully and slightly turning the astigmatism and focus pots suggests intermittent contact?
Did you check the Display Control Board (A2) and its connections to the outside world?

Raymond


Re: [Tek 485] No intensity control

marcosjl31@...
 

Ozan

On DC RESTORER side : I changed all the diodes that are in the High Voltage zone (below the plastic shield) on the Horiz Amp Board as 3 of them were dead, and there have been some repair attempt on 3 other ones in the same DC Restorer area. This modification give me back some Intensity control at least for Time Div <20ms. For 50ms, .5s, .2s and .1s as well as the X-Y mode I do not even get a trace ! (and that's new).

I do not see any dot when in X-Y mode or in lowest Time/div positions => This seems to point out something wrong elsewhere.

R1660 modifies voltage at CR1660 cathode from ~+79V to +120V. Currently I set arbitrary 105V reading by adjusting R1660 => In normal mode it gives me a normal range of intensity control.

Jose


Re: 7104 out of focus/astigmatism

Francesco Franzini
 

Dear Jean-Paul, Raymond

I investigated deeply on HV board, testing almost all components, since i am well aware of the problem related to HV circuits, i decided to swap the entire board taken from well working 7104, on 7104 HV transformer, multiplier and everything else are on the HV board, then i essentially replaced all of the HV circuits, to be absolutely sure i swapped (from the same working 7104) PSU and Z board.

Before the "board swapping" i reviewed all of the voltage level and connection, including CRT socket as per previous advice.

Raymond, i am curious on the meaning to "tilt the scope" can you please elaborate on that ?

After your replies i am thinking to inspect the HV connection from the multiplier to the CRT tube so check for leakage, does this make any sense?

This situation is really puzzling me because the CRT seems to be in very good condition and in any case i will try to find the root cause of this issue, fortunately i have a second completely working 7104 scope to use to swap boards and components.

Any other advices are more than welcome

Thank you
Francesco

Francesco


TDS3064B "ripple" on calibrator signal

 

Running an up-hacked TDS3014B, and am seeing small amount of what I'll call
"ripple" on the top of the calibrator signal (i.e. the 5V part of the signal
- the 0V end is relatively stable by comparison). By "ripple" I mean it's
dancing up and down quite slowly (2Hz?) by about 1/2 a trace width, and the
Ch1 Max value switches between 5.16V and 5.20V.

Has anyone here seen this sort of behaviour before?

Thanks
David


Re: 7104 out of focus/astigmatism

 


i found something strange on TP1784, voltage level (+98.6) ok but very high and variable
ripple, when the scope is out of focus/astigmatism the ripple is 4 to 6 volt 2.5ms period
then, after about 30 min, drop to 1 volt 2.5ms period and everything is working right.
You may direct your attention to checking out the HV control loop circuits (around components x177y and x178y). Did you follow the CRT troubleshooting as described in the SM, especially step D?

I don't immediately see where a 2.5ms (400 Hz??) ripple could be coming from. Oscillation in the HV control loop? I don't immediately see time constants that may be involved.

Did you check R1805 (HV adjust)? Note its approximate position, move it back and forth a bit and see if it's "scratchy". You may even switch off power, exercise the pot, put it back in its original position and see what happens after power on. You may note the amplitude of a standard signal on the screen when the instrument is working OK before and readjust R1805 to that afterward, to at least approximate its original position.

According to the SM, you may temporarily remove Q1784 (opening the HV stabilization loop) and measure/observe.

If, with Q1784 temporarily out, the problem disappears, the DC restorers are less suspect and the control loop (via TP1806) may be at fault. You may temporarily short TP1806 to GND to see if the problem stays away.

Zeners fail, especially HV ones, develop leaks. VR1784 (200V) may have a problem.
Does the problem occur while Q1784 is removed from the circuit? If not, the HV voltage regulation may be at fault.
You may consider just replacing U 1802 (a uA741), that is, if it's socketed.

Raymond

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