Date   

Re: 577 D2 question(s)

Dave Voorhis
 

On 3 May 2021, at 22:04, Dave Voorhis via groups.io <voorhis=gmail.com@groups.io> wrote:

On 3 May 2021, at 20:02, Andy Warner <andyw@pobox.com> wrote:

...
Any 577 owners out there got advice to share ?
My first 577 (a D1) was very dim — and it came with a spare CRT — but essentially worked for a while after I got it home. Then it suddenly went completely dark. Rapid onset blackness seemed unlikely to be CRT wear so I checked the Z-axis and sure enough, two transistors (I don’t recall which) in that circuit had failed.
I thought there was a chance I might have made notes of the repair, and sure enough I did:

Q1234 151-0406-00 Transistor:PNP:TO-39 04713 ST1264 2N5401
Q1226 151-0347-00 Transistor:NPN:TO-92 04713 SPS7951 2N5551


Re: 7CT1N plugin boards

 

I just received the boards about a week ago. They're beautiful, and deceptively small, but it was obvious that they fit the 7CT1N on even the most cursory inspection.

Now I'm just waiting on the banana plugs and switch.

Thanks

-- Jeff Dutky


Re: 577 D2 question(s)

Dave Voorhis
 

On 3 May 2021, at 20:02, Andy Warner <andyw@pobox.com> wrote:

I bought a mostly working 577/D2 recently.
What I regard as the most serious problem with it is the trace intensity.

What I see is that the maximum intensity occurs at approx 60% of the front
panel adjustment (R1200) - moving it either direction from the peak results
in a dimmer trace.
The bulk of the trace (when the beam is moving fast) is not particularly
bright, but the start and end of the traces is good.

I have cleaned and checked R1200 operation, and I believe the pot is good.

Also, the dimming signal from the collector supply board (R592) seems to be
correct (e.g. near zero V when the collector voltage is non-zero.) However,
I don't really see an obvious dimming effect on the trace when I turn the
collector supply down to zero.

I have not yet been able to measure the HT voltage (looking for a probe to
help me do that - advice welcome.)

In the interim, I wanted to trace the operation of the Z amplifier circuit
(Q1222,1226,1234), but the service manual I have (thank you Artek) is
silent on removing the deflection amp/high voltage board.
It honestly looks like a royal pain to remove for service - does anyone
here have any hints and tips ?
The schematic has a couple of helpful waveforms shown, but I have zero idea
how you are expected to probe up the board, given the location of the
side-rail that obscures the lower half of the board.

Any 577 owners out there got advice to share ?
My first 577 (a D1) was very dim — and it came with a spare CRT — but essentially worked for a while after I got it home. Then it suddenly went completely dark. Rapid onset blackness seemed unlikely to be CRT wear so I checked the Z-axis and sure enough, two transistors (I don’t recall which) in that circuit had failed.

But afterward it was as dim as before, and with similar behaviour to what you describe — brightest in roughly centre travel, dimmer either higher or lower.

I replaced the CRT with the spare it came with and that fixed it. Hopefully not the case with yours.

My second 577 (another D1) was also a tad dim — but not as bad as my first — and also reaching a peak somewhat past centre brightness. Notably, it has improved with use and whilst not the brightest CRT I’ve ever seen, more than usable.

With both units I went through the calibration procedure, including checking/setting HT voltage. I checked it with an older VOM that goes to 5000 volts, taking all reasonable precautions to hook it up carefully with good well-insulated leads and clips and make sure I’m not anywhere near, let alone touching, any possible conduction path whilst it’s powered.

The dimming effect of turning down the collector voltage should happen only in the last degree or so of rotation, essentially when it hits the zero position.


Re: Transporting a 500-Series Scope without Breaking the CRT

 

Kieth,

Thanks for the reply, but it's about 24 hours too late to help. Also, a spare Tek CRT box is a big ask, at least for me (it's hard to have any "spares" when the total number on hand is zero).

I did not hear any sound of a CRT's vacuum escaping (whether "thunk" or "wump" or however you choose to transliterate the unspoken noise), so if the CRT is dead it was not by my hand. The scope was not in a condition to be powered up, so there was no way to verify that the CRT was working. I'm sure the previous owner is willing refund my entire purchase price if there are any problems ;-P

Seriously, I've already done some research on how much it would cost to replace the CRT. It looks like there are replacement units available, and that they're not outrageously expensive. It also looks like its a bit of a gamble if any of them actually work, or will survive the shipping.

-- Jeff Dutky


Re: PG506 Repair - I had a Great Day today/

-
 

Mark,

I absolutely agree about using 400 to 600 volt parts for the X and Y
caps. I have connected a GOOD Power Line Disturbance Analyzer to the power
lines and 350 volt spikes are not at all uncommon on the 115VAC line. I
saw ~325 volt spikes in both the + and - half cycles *every* time that I
switched on an Astron switching power supply.

On Mon, May 3, 2021 at 3:41 PM Mark Vincent <orangeglowaudio@gmail.com>
wrote:

-

You are right for sine wave being 1,414.... For square wave, also PWM, it
is 1,5x. To make sure the caps, rectifiers, transformer, etc. is not being
stressed, use 1,5x RMS or higher. This gives extra headroom. Double is not
always necessary. I did see a large reduction in the output temperature of
the computer power supply after pulling out the 16V caps on the 12V line
and putting in good 25V ones. The heatsink, transformer and air coming out
is cooler. When Rene finds the source of why his transformer is getting
hot, I would like to know what was causing the heating. What I said to
check is what could cause that problem. Checking and testing will confirm
one way or the other. He has done a lot and learned a lot. He is checking
everything step by step narrowing down things while keeping a record of
things done. That is the proper diagnostic way.

An X or Y cap off the mains I would agree to at least double the RMS
voltage and get one rated at or above that, e.g. 400-600V for 120/240V
mains.

Mark






Re: What's a chat.. and why?

teamlarryohio
 

Michael, I saw that and thought 'we have 8000 people who read the emails/posts, and about 10 that even knew there was a chat server available.' There are open chats out there from 2018! I think the posting and mailing might be a better way to reach a larger audience :-)
-ls-


561A early s/n HV supply

Ondrej Pavelka
 

Hi folks,

I have acquired 561A which looks in decent condition visually but the HV transformer and associated valves and caps are all missing. I can see somebody attempted to make replacement HV supply and failed in doing so and put the scope to side. When his kids were doing a cleanup I bought it without checking as it was cheap enough and I don't have any valve Tek scope.
Rest of the HV supply is easy to make using diodes and fresh new caps but the transformer is a show stopper. I couldn't find many floating about for sale but by an off chance aren't the original transformer specs available? I can have one made but it will be much easier if I know the exact spec.


Re: 577 D2 question(s)

ChuckA
 

Andy

Removing the HV board is a PIA as you have to unsolder 11 or so connections on the top of the board and a screw holding the heat sink for the oscillator transistor before you can work it out. Gets easier the second or third time. I wish TEK had used push on connectors like on the 576 boards.

Be careful bending the plastic clip in supports that hold the board, very easy to snap off.

Definitely was a bad design for working on the board in the cabinet, should have had the side rail removable.

Chuck

On 5/3/2021 3:02 PM, Andy Warner wrote:
I bought a mostly working 577/D2 recently.
What I regard as the most serious problem with it is the trace intensity.

What I see is that the maximum intensity occurs at approx 60% of the front
panel adjustment (R1200) - moving it either direction from the peak results
in a dimmer trace.
The bulk of the trace (when the beam is moving fast) is not particularly
bright, but the start and end of the traces is good.

I have cleaned and checked R1200 operation, and I believe the pot is good.

Also, the dimming signal from the collector supply board (R592) seems to be
correct (e.g. near zero V when the collector voltage is non-zero.) However,
I don't really see an obvious dimming effect on the trace when I turn the
collector supply down to zero.

I have not yet been able to measure the HT voltage (looking for a probe to
help me do that - advice welcome.)

In the interim, I wanted to trace the operation of the Z amplifier circuit
(Q1222,1226,1234), but the service manual I have (thank you Artek) is
silent on removing the deflection amp/high voltage board.
It honestly looks like a royal pain to remove for service - does anyone
here have any hints and tips ?
The schematic has a couple of helpful waveforms shown, but I have zero idea
how you are expected to probe up the board, given the location of the
side-rail that obscures the lower half of the board.

Any 577 owners out there got advice to share ?
--
See Early TV at:

www.myvintagetv.com


Re: TDS 380 Attenuator Resistor Replacement Specs

Richard Peterson
 

Thanks for the feedback Ozan. Here are the errors I get:

https://groups.io/g/TekScopes/photo/263498/3219273?p=Created,,,20,2,0,0
https://groups.io/g/TekScopes/photo/263498/3219271?p=Created,,,20,2,0,0
https://groups.io/g/TekScopes/photo/263498/3219272?p=Created,,,20,2,0,0


- It does appear that the memory is not the issue. Swapping hybrids would be a very difficult undertaking from what I've read in another post by Dave Wilson . . . he tried to de-solder one to work on it using better equipment than i have and finally gave up.

I'll take some measurement to see if the -2VDC changes with offset adjustments. There is not a corresponding opposite DC voltage on the POS_OUT pin.
I'll also try the SPC and will spend some more time signal tracing both channels to look for differences that could help narrow the search.

Rich


Re: Transporting a 500-Series Scope without Breaking the CRT

Keith
 

Those 5 series CRT like the 5CAP1, etc. are prone to crack at the neck where the four beam former leads come out. If I recall correctly, there's supposed to be some foam in that neck support ring, but rest assured it will be long gone. The neck support ring is a bad idea, because if the scope bangs around - even a little - it puts awkward leverage on the neck of the tube. Don't ask how I know, but if you ignore this and just chunk it in the car, then don't be surprised to hear the "thonk" sound of a CRT breaking...right at those four pins on the neck.

Personally, I would take the CRT out and box it in a spare OEM tek CRT box (if you have one). Really, it isn't that hard to get out. I had mine out in less than five minutes.


Re: TDS 380 Attenuator Resistor Replacement Specs

Ozan
 

Hi Richard,
I don't have a TDS380 but I have debug experience on TDS520, TDS520A, and TDS7104. Looking at schematics briefly TDS380 looks similar.

- pin 15 and 16 (GND/OS and OFFSET). CH1 shows -2VDC and CH2 shows 0VDC.
- pin 28 (NEG_OUT). CH1 shows 0.25 VDC and CH2 shows 0.03 VDC.
Do you see a voltage of opposite polarity (i.e. -0.25V) at POS_OUT of Ch1?


Still no signal display for CH1 except a negative offset flat line which makes
sense given the -2VDC reading on the offset pin of the attenuator. DC offset
on the display for CH1 shows 0V . . . .
If you add offset from front panel (I don't know if TDS380 has that menu) or move vertical control does the -2VDC offset change?

The offset is sum of two parts: one is the offset set by front panel input, the other part is a calibration constant (actually two, DC balance and hybrid offset). On a TDS520/520A/TD7104 SPC (signal path compensation) menu self calibrates these constants. You may want to run SPC (procedure is in the service manual) to check if Ch1 recovers.

If Ch1 is still bad after SPC you can try swapping the hybrids between Ch1 and Ch2 to see if problem moves with hybrid or stays at Ch1. Since hybrid and Daculator U202 is in a calibration loop it is difficult to tell if the problem is with the hybrid of Daculator path. Swapping channels, especially when one is known good, is the quickest path to find the faulty block.

I'll spend some time checking components in the offset circuit next, but I've
read more than a few posts where problems with the TDS3xx scopes are
frequently tied back to the SRAM IC - AS7C164–12JCTR.
It is unlikely SRAM is the root cause of the problem you are seeing.

Ozan


Re: PG506 Repair - I had a Great Day today/

Mark Vincent
 

-

You are right for sine wave being 1,414.... For square wave, also PWM, it is 1,5x. To make sure the caps, rectifiers, transformer, etc. is not being stressed, use 1,5x RMS or higher. This gives extra headroom. Double is not always necessary. I did see a large reduction in the output temperature of the computer power supply after pulling out the 16V caps on the 12V line and putting in good 25V ones. The heatsink, transformer and air coming out is cooler. When Rene finds the source of why his transformer is getting hot, I would like to know what was causing the heating. What I said to check is what could cause that problem. Checking and testing will confirm one way or the other. He has done a lot and learned a lot. He is checking everything step by step narrowing down things while keeping a record of things done. That is the proper diagnostic way.

An X or Y cap off the mains I would agree to at least double the RMS voltage and get one rated at or above that, e.g. 400-600V for 120/240V mains.

Mark


577 D2 question(s)

Andy Warner
 

I bought a mostly working 577/D2 recently.
What I regard as the most serious problem with it is the trace intensity.

What I see is that the maximum intensity occurs at approx 60% of the front
panel adjustment (R1200) - moving it either direction from the peak results
in a dimmer trace.
The bulk of the trace (when the beam is moving fast) is not particularly
bright, but the start and end of the traces is good.

I have cleaned and checked R1200 operation, and I believe the pot is good.

Also, the dimming signal from the collector supply board (R592) seems to be
correct (e.g. near zero V when the collector voltage is non-zero.) However,
I don't really see an obvious dimming effect on the trace when I turn the
collector supply down to zero.

I have not yet been able to measure the HT voltage (looking for a probe to
help me do that - advice welcome.)

In the interim, I wanted to trace the operation of the Z amplifier circuit
(Q1222,1226,1234), but the service manual I have (thank you Artek) is
silent on removing the deflection amp/high voltage board.
It honestly looks like a royal pain to remove for service - does anyone
here have any hints and tips ?
The schematic has a couple of helpful waveforms shown, but I have zero idea
how you are expected to probe up the board, given the location of the
side-rail that obscures the lower half of the board.

Any 577 owners out there got advice to share ?
--
Andy


Re: Challenging 2465 PS repair

-
 

Thanks for the added info Harvey. That's one of the reasons why I always
start my Variac at very low voltage (~1 VAC) and watch the Ammeter for a
good minute before I start *slowly* start increasing the voltage. If I get
any current that approaches the rated operating current (at 110VAC or
whatever) then I KNOW that there's a problem but as long as the current
draw stays *below* the rated current then it shouldn't cause any damage.

On Mon, May 3, 2021 at 2:14 PM Harvey White <madyn@dragonworks.info> wrote:

The undervoltage damage theory isn't a theory under certain circumstances.

It all depends on how the switching is done.

If the pass element always switches, and has a current limit, then it's
protected.

Some supplies don't. I've see designs where there is a minimum required
voltage to start switching, and the transistor is full on until the
switching starts. If there's no protection, then you can get damage.
Bad design? Yes, but it's possible to do and you may not be aware that
you have one.

That's what I'd say would be the problem. Pass transistor on
(especially if it's a boost supply and not a buck supply).

Be aware, just in general, that some of the inexpensive boost or buck
modules coming out of China may behave like this. Running them on a
current limited supply will let you know.

Does your supply do this? Don't know. Could it? Maybe...

If I run a scope or piece of test equipment off a variac, I'm watching
the input current, and also a bit of the outputs to see what the
regulator is up to.

Harvey


On 5/3/2021 1:47 PM, - wrote:
The equipment that I usually work on is usually too old to use a
switching PSU. Also I've NEVER had a switcher fail by using it on a
Variac.
IMO there is a big difference between "it's theoretically possible to"
and
"likely too". I've *operated* literally thousands of smaller switching
PSUs
at extremely reduced voltages and never seen one that damaged itself by
drawing "excessive" current. Sure, they will draw more current at reduced
voltages but, in my experience, *never* enough to damage themselves. I
say
"operated" loosely, since at very reduced voltages (< ~60%) they will
not
operate and their current draw drops to near zero. Let me also point out
that as part of their Performance Tests, HP and others frequently call
for
attempting to operate their equipment at both reduced and excess
voltages.
Also I don't ever recall seeing a warning in a HP manual saying that
attempting to operate their equipment below XXX voltage *would* cause
damage.

YMMV

PS does anyone have a few switching PSUs that they're willing to
possibly sacrifice, in order to test and see how low their input voltage
can go before they stop operating and if very low input voltages will
damage them? Maybe we can finally prove or disprove the "under-voltage
=
damage" theory.



On Mon, May 3, 2021 at 11:59 AM Tom Gardner <tggzzz@gmail.com> wrote:

Since a *switching* PSU will attempt to deliver a constant output
power, a low input voltage means a high input current flowing through
transistors, diodes and some capacitors.

An abnormally high current might cause damage.

On 03/05/2021, Milan Trcka <milan.v.trcka@gmail.com> wrote:
In an attempt to keep in as much smoke as possible when powering up
suspect
or failed PS, I use an adjustable transformer (Variac) to slowly bring
up
mains voltage while monitoring for vital signs. Use isolation
transformer or
battery powered isolated scope when monitoring waveforms.

M
















Re: Challenging 2465 PS repair

Harvey White
 

The undervoltage damage theory isn't a theory under certain circumstances.

It all depends on how the switching is done.

If the pass element always switches, and has a current limit, then it's protected.

Some supplies don't.  I've see designs where there is a minimum required voltage to start switching, and the transistor is full on until the switching starts.  If there's no protection, then you can get damage.  Bad design?  Yes, but it's possible to do and you may not be aware that you have one.

That's what I'd say would be the problem.  Pass transistor on (especially if it's a boost supply and not a buck supply).

Be aware, just in general, that some of the inexpensive boost or buck modules coming out of China may behave like this.  Running them on a current limited supply will let you know.

Does your supply do this?   Don't know.  Could it?  Maybe...

If I run a scope or piece of test equipment off a variac, I'm watching the input current, and also a bit of the outputs to see what the regulator is up to.

Harvey

On 5/3/2021 1:47 PM, - wrote:
The equipment that I usually work on is usually too old to use a
switching PSU. Also I've NEVER had a switcher fail by using it on a Variac.
IMO there is a big difference between "it's theoretically possible to" and
"likely too". I've *operated* literally thousands of smaller switching PSUs
at extremely reduced voltages and never seen one that damaged itself by
drawing "excessive" current. Sure, they will draw more current at reduced
voltages but, in my experience, *never* enough to damage themselves. I say
"operated" loosely, since at very reduced voltages (< ~60%) they will not
operate and their current draw drops to near zero. Let me also point out
that as part of their Performance Tests, HP and others frequently call for
attempting to operate their equipment at both reduced and excess voltages.
Also I don't ever recall seeing a warning in a HP manual saying that
attempting to operate their equipment below XXX voltage *would* cause
damage.

YMMV

PS does anyone have a few switching PSUs that they're willing to
possibly sacrifice, in order to test and see how low their input voltage
can go before they stop operating and if very low input voltages will
damage them? Maybe we can finally prove or disprove the "under-voltage =
damage" theory.



On Mon, May 3, 2021 at 11:59 AM Tom Gardner <tggzzz@gmail.com> wrote:

Since a *switching* PSU will attempt to deliver a constant output
power, a low input voltage means a high input current flowing through
transistors, diodes and some capacitors.

An abnormally high current might cause damage.

On 03/05/2021, Milan Trcka <milan.v.trcka@gmail.com> wrote:
In an attempt to keep in as much smoke as possible when powering up
suspect
or failed PS, I use an adjustable transformer (Variac) to slowly bring up
mains voltage while monitoring for vital signs. Use isolation
transformer or
battery powered isolated scope when monitoring waveforms.

M











Re: PG506 Repair - I had a Great Day today/

-
 

The *Peak* voltage of a (true sinusoidal) AC signal is 1.4(something)
times the RMS voltage (the point that most AC signals, transformers, etc
are rated at) so the caps MUST be rated at more than 1.4 times what the
transformer output is. I would go with caps rated at at least twice the RMS
voltage.

My $.02 worth,

On Mon, May 3, 2021 at 1:26 PM Mark Vincent <orangeglowaudio@gmail.com>
wrote:

Rene,

I see you said you recapped the unit. For the caps in the primary power
section, they should be a low ESR high temp type, e.g. Nichicon ULD, UCY,
etc.

Mark. You may have used this type already. The one for the 120V supply
should be 200V. The heat will reduce with low ESR types provided the rated
voltage on the caps are high enough. If the voltage is lower than the peaks
of the unfiltered ac, it heats the caps up and causes higher power to be
dissipated in the driver transistors and transformer. For square wave
oscillation, the minimum rated voltage for caps is 1,5x the rated ac
voltage from a winding. It is possible the additional heat is from a ,1mfd
that is leaking that is on the -72V line.

Check VR210. If that is bad, the AMPL VAR, R225A, will not work right.
Michael Lynch is right about checking the diodes.

Mark






Re: Tektronix Probe Replacement Parts and Accessories

+1 925-334-8641
 

Thanks, Dennis. This is very informative.


Re: Challenging 2465 PS repair

-
 

The equipment that I usually work on is usually too old to use a
switching PSU. Also I've NEVER had a switcher fail by using it on a Variac.
IMO there is a big difference between "it's theoretically possible to" and
"likely too". I've *operated* literally thousands of smaller switching PSUs
at extremely reduced voltages and never seen one that damaged itself by
drawing "excessive" current. Sure, they will draw more current at reduced
voltages but, in my experience, *never* enough to damage themselves. I say
"operated" loosely, since at very reduced voltages (< ~60%) they will not
operate and their current draw drops to near zero. Let me also point out
that as part of their Performance Tests, HP and others frequently call for
attempting to operate their equipment at both reduced and excess voltages.
Also I don't ever recall seeing a warning in a HP manual saying that
attempting to operate their equipment below XXX voltage *would* cause
damage.

YMMV

PS does anyone have a few switching PSUs that they're willing to
possibly sacrifice, in order to test and see how low their input voltage
can go before they stop operating and if very low input voltages will
damage them? Maybe we can finally prove or disprove the "under-voltage =
damage" theory.

On Mon, May 3, 2021 at 11:59 AM Tom Gardner <tggzzz@gmail.com> wrote:

Since a *switching* PSU will attempt to deliver a constant output
power, a low input voltage means a high input current flowing through
transistors, diodes and some capacitors.

An abnormally high current might cause damage.

On 03/05/2021, Milan Trcka <milan.v.trcka@gmail.com> wrote:

In an attempt to keep in as much smoke as possible when powering up
suspect
or failed PS, I use an adjustable transformer (Variac) to slowly bring up
mains voltage while monitoring for vital signs. Use isolation
transformer or
battery powered isolated scope when monitoring waveforms.

M










Re: TDS 380 Attenuator Resistor Replacement Specs

Richard Peterson
 

A little progress. I now have a signal through the CH1 relays on the attenuator board and the voltage readings on all the pins match between CH1 and CH2 except:
- pin 15 and 16 (GND/OS and OFFSET). CH1 shows -2VDC and CH2 shows 0VDC.
- pin 28 (NEG_OUT). CH1 shows 0.25 VDC and CH2 shows 0.03 VDC.

Still no signal display for CH1 except a negative offset flat line which makes sense given the -2VDC reading on the offset pin of the attenuator. DC offset on the display for CH1 shows 0V . . . .

I'll spend some time checking components in the offset circuit next, but I've read more than a few posts where problems with the TDS3xx scopes are frequently tied back to the SRAM IC - AS7C164–12JCTR.

Your feedback would be appreciated.


Re: What's a chat.. and why?

Michael W. Lynch
 

I did not realize that we could chat, silly me. I just I never paid attention to the menu, skipped right over that part.. Kind of like the "POLL" feature; not used much in this group, but part of the "groups.io" package. I can see the occasional benefit of chat, but chat is not the best way to share to the broader audience on this forum.

--
Michael Lynch
Dardanelle, AR

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