Date   

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

Ananda
 

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


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

Mark Vincent
 

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: Challenging 2465 PS repair

-
 

I do the same but I have an amp meter attached to my Variac and I start
out at about 1 VAC and watch for excessive current. If the device under
test is rated to draw say 5 amps at 115 VAC and I apply say 3 VAC and it's
already drawing 3 Amps then there's probably a short somewhere. But the
low amount of power (9 Watts) isn't as likely to cause damage as applying
115 VAC and 20 Amps (the normal limit of 115 VAC circuits) would.

On Mon, May 3, 2021 at 11:46 AM 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: Transporting a 500-Series Scope without Breaking the CRT

stevenhorii
 

In the UPS facility I used to ship items from (Gardena, CA) they had a sign
on the wall saying “pack for a four-foot drop onto concrete”. I took them
at their word. I had a rare Mercury spacecraft horizon scanner, so I used
mil-spec packing for it. In it’s own fiberglass shipping box and that into
a cube-shaped box with about four inches of foam around all sides. At the
UPS facility, they put it on the scale and said there was a surcharge
because the item was “too large for the weight”. I pointed to the sign and
told them it was packed to meet that requirement. They didn’t care - that
was their policy. I understand this - their thinking is that it takes up
more space than it is “worth” in an air cargo container or truck so their
surcharge is to offset that “opportunity cost”. Some pencil-pusher probably
figured out that it costs them less to pay the (rare) claim rather than the
opportunity cost of not packing more boxes in the shipping container or
vehicle.

I also had a Spacelab computer in its transit case (high-density
polyethylene with plenty of fitted fairly stiff foam inside). When I
received it, the plate with the handles and all the connectors was dented
in. It must have been dropped far enough that the computer banged into the
inside of the container. UPS said “inadequately packed” and would not back
down despite photos. Fortunately, the guy who sold me the computer had
spare parts from one he parted out and he sent me a replacement end plate.
The internal electronics had not been damaged.

If I do have Tek scopes shipped, if they are plug-in types (7000-series,
etc) I always tell the shipper to remove any plug-ins and pack them
separately. I offer to pay extra shipping and packing costs if necessary. I
also tell them to put a layer of styrofoam or polyethylene foam over the
face of the scope to protect the knobs on the front. The best sellers have
done this and more. One wrapped the scope (a 7854) with about six inches of
bubble on all sides plus an additional two inches over the front and then
put two crossed-layers of corrugated cardboard in front of that. It went
into a double-wall box. It was shipped to me cross country and was handled
by FedEx Ground. The scope arrived in fine condition and worked when
powered up. I also always check for loose parts (rattles, etc) before
applying power.

On Mon, May 3, 2021 at 10:56 Greg Muir via groups.io <big_sky_explorer=
yahoo.com@groups.io> wrote:

Back in the late 90’s I had a small piece of equipment that was captured
in a military shipping container consisting of 2” closed cell stiff foam
shock absorbers around each corner of the unit faced with an aluminum layer
on each one. The transit container consisted of .062” aluminum walls both
inside and outside with a 3/8” layer of plywood sandwiched in between the
aluminum. The unit itself weighed around 20 pounds with the container
coming in a close second.

When received from UPS Ground the knobs (or at least the parts of them
with the control shafts) were sticking out through the exterior aluminum.
Needless to say the unit was toast. The UPS inspector tried to tell me
that the unit was “inadequately packed.” I told him that my impression
was that the container must have been dropped from at least a 10 foot
height onto a concrete floor.

UPS begrudgingly reimbursed the cost of the unit but would not refund the
shipping charges.

Greg






Re: Challenging 2465 PS repair

Siggi
 

On Mon, May 3, 2021 at 3:54 AM satbeginner <castellcorunas@gmail.com> wrote:

After studying the schematic of this power supply, it is vaguely similar
to the 22xx power supplies, but with at least one major difference.

Similar is, it has a Primary switcher, and it has a secondary switcher,
but, were in the 22xx PS the secondary switcher runs at it's own frequency,
in this 246x PS the secondary switcher uses the same frequency as generated
by the primary switcher.
This makes it a bit more of a challenge to separate the Primary and the
Secondary to test them one at the time.
Switchers will run just fine on DC input, and if you have a suitable bench
supply to run it from, that gives you two big benefits:
1. Limited energy input, the current limit could be set low enough that
nothing blows up.
2. Mains isolation, so you can now peek around anywhere with your scope.

Unfortunately the DC bus on this scope runs at 2-300V (I see a 264V
annotation on the schematic), using an AC voltage doubler when on 115V
input, and not many bench supplies have that sort of voltage output. I do
find that switchers will often start way below their supposed minimum input
voltage, which may work just fine for diagnosis. You really don't want to
load them - as others have mentioned - with a low input voltage.


Re: Tektronix Probe Replacement Parts and Accessories

Rogerio O
 

Thank you very much for sharing your work.
I had spent a lot of time trying to figure out the correct Tek part number of the probe parts I was willing to buy....
Roger


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

Ondrej Pavelka
 

I believe it allows people to join online for instant messaging, could be
very helpful for some brain storming or troubleshooting session.

On Mon, 3 May 2021, 01:27 Roy Thistle, <roy.thistle@mail.utoronto.ca> wrote:

Hi:
I saw the post on the 2430A was as a chat?
Do we do that on TekScopes?
And why would someone want to? ... What's the advantage of that over
starting/participating in a thread?
It appears that chats are in the sub-basement of TekScopes.
--
Roy Thistle






Re: Challenging 2465 PS repair

 

The 2465 PSU is a switcher, so a variac is strongly counter indicated as this will typically cause the PSU to draw excess current at low voltages (below the nominal range of say 100-120V, or 200-240V over here).

D.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Milan Trcka
Sent: 03 May 2021 16:46
To: TekScopes@groups.io
Subject: Re: [TekScopes] Challenging 2465 PS repair


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

Tom Gardner
 

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

Milan Trcka
 

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


Tek 465 - help is needed...

Dr. Manfred K. Zeller
 

Channel 1 Beam with the Beam Finder cannot regulated down over the whole screen with the position knob - it is only on the upper side of the screen.
Only a little - two or three scales.

Result: no Beam in channel 1

Channel 2 is working.

Voltage: ok
Manual: there

Thanks!
Regards
Manfred


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

Greg Muir
 

Inspectors have a tendency to come out of the woodwork when the insurance value equals several months or more of a mid-level managers income.

Greg

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