Date   
Re: 2402a Tekmate troubleshooting

cmjones01
 

On 6 Apr 2017 8:46 p.m., "szigszabolcs@... [TekScopes]" <
TekScopes@...> wrote:

I did see activity on the CPU bus with a scope, so something is going on,
but there is definitely nothing on the EGA. I plugged in a keyboard, caps
lock, num lock leds don't work, so it's not getting far enough to
initialize the BIOS keyboard routines.


Does it have a speaker connected? If it's running but there's a problem
with the RAM or the video, it should give a beep code which indicates
what's wrong.

Chris

Re: Tek Support experience

 

All's well that ends well! I have my new DD-52 display.


I learnt a couple of things here:
1. Email communications are a waste of time, if there's a problem. A phone call gets things done.
2. The techs on the phone are super people, who really want to help, and overcome obstacles.
3. The tech representative who gets the most kudos here is Gail Rutledge - she didn't give up - I post her contact details here, simply because she deserves the credit, and so that if anyone else needs a DD-52 display, she'll be the person to help.
gail.rutledge AT tektronix.com
4. The cost was $62 + shipping.


Kudos to Tek - they're still on the map!


Menahem

Re: 2402a Tekmate troubleshooting

Szabolcs Szigeti
 

Hi,

Thanks. I've already read you page, while this was being shipped, lots of valuable info, thank you for that..
Yes, the power seems to be all right, +5, +12, -12 are all there. The ripple is below 100mV, whic, i don't have spec on, but I think should be acceptable.
Since I've already taken it apart, i'll be removing the nvram and adding a bettery to itanyway, that wouldn't hurt. Once that done, I can continue troubleshooting.
I did see activity on the CPU bus with a scope, so something is going on, but there is definitely nothing on the EGA. I plugged in a keyboard, caps lock, num lock leds don't work, so it's not getting far enough to initialize the BIOS keyboard routines.
Also, I'm planning to find an ISA VGA card, and i'll be pulling the BIOS eproms to see if they have their content.
Then we'll see. I'd really like to get it working, just for the fun of it.


Szabolcs

Re: 2402a Tekmate troubleshooting

Paul Amaranth
 

A dead NVRAM will just make it boot up with the default date and
parameters; that's probably not the reason it isn't doing anything.
Did you check the power supply output?

The NVRAM was dead on the one I got working.

And, Raymond, thanks for the plug :-)

Paul

On Thu, Apr 06, 2017 at 02:01:20PM +0000, @Raymond [TekScopes] wrote:
Hi Szabolcs,
Have a look over here:
<http://www.auroragrp.com/agi/other/tekmate/tekmate.html>
The site is run by a member of this group.

Raymond





!DSPAM:58e648b9323501857611428!
--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows

Re: 7623A power supply low

Brent Watson <brentleew2003@...>
 

Sorry Dave, it was late for me, and I probably erred.
Both the Base and Emitter of U973 are negative with respect to ground.Base -4.38   Emitter  -0.730

Re: Variac + Isolation Transformer Question

 

Yes it's the plugs that are fused, not the sockets - sorry I should have made that clearer.

Dave

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 06 April 2017 13:10
To: TekScopes@...
Subject: Re: [TekScopes] Re: Variac + Isolation Transformer Question

Unless there has been a massive change in the wiring regulations, no power outlet in the UK is fused.

Re: 7623A power supply low

Dave Hills
 

Previously you stated " The voltages at U973E are: Base 4.36v Emitter .731v Collector 2.350v." Now you say "Base to ground is -4.37v and should be -.03 Emitter to ground is -.72v and should be -.7 Collector to ground is 2.4v and should be +7.1."
So, which is it? Are the base and emitter voltages positive or negative with respect to ground?

Dave

Re: 2402a Tekmate troubleshooting

 

Hi Szabolcs,
Have a look over here:
<http://www.auroragrp.com/agi/other/tekmate/tekmate.html>
The site is run by a member of this group.

Raymond

2402a Tekmate troubleshooting

Szabolcs Szigeti
 

Hi,

I'm now a lucky owner of a Tekmate which I got in unknown state. It had a HDD and an EGA card. Came with it a 2430a, which will be probably sold, as I already have a 2440. Although I may swap the front panel first, as it is in a much better nick. The battery needs to be replaced in the 2430a, it still works, but fails the FPP/nram battery test. But that can come later.

However, the Tekmate looks like it does not start. The power supply and the fan starts, the HDD spins up, but no other visible activity. No beeps, no FDD/HDD led activity, nothing.

I'm still finding a way to hook up some monitor to the EGA output, but I did check with a scope and I do not see any signals on the EGA output.

In the meantime do you have any ideas on where to start troubleshooting? I'll check the power supply and ripple once I get this thing apart.

Would a discharged Dallar nvram chip make it completely dead? It has a 88 date code, so it is probably flat by now.

Thanks,

Szabolcs

Re: 7623A power supply low

Brent Watson <brentleew2003@...>
 

Dave, Roger,
I didn't measure the B-E and B-C , I was reading 12, 13, and 14 to ground as per the schematic.  U973E  B-E is 3.62 And B-C is 6.72As per the schematic the Base to ground is -4.37v and should be -.03    Emitter to ground is -.72v and should be -.7    Collector to ground  is 2.4v and should be +7.1.  As it happens I have a 7b53a so will try the Ca3046 swap.....      I swapped the array and got exactly the same voltage readings as with the ca3046 originally installed.  (my 7b53a uses the 156-0048-00, but it is still an RCA CA3046)       Brent


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Re: 7623A power supply low

Jerry Massengale <jmassen418@...>
 

Hi,

Thanks Raymond, I am only on my third coffee.

jerry

On Thu, Apr 6, 2017 at 6:58 AM, @Raymond [TekScopes] <
TekScopes@...> wrote:



u973 is a ca306
@Jerry,
That's a typo; Officially, it's a CA3045F (156-0065-00), CERDIP package,
like a common CA3046, PDIP package. AFAIK, only packages different.

Raymond

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[Non-text portions of this message have been removed]

Re: Variac + Isolation Transformer Question

Brian <brianclarke01@...>
 

Unless there has been a massive change in the wiring regulations, no power outlet in the UK is fused.
The plug top contains a fuse holder that can be populated with fuses ranging from 1 A to 13 A.
The main purpose of the ring main was to achieve a ‘kind of’ 30 A distribution using 15 A wire in order to reduce IR loss, not I-squared R loss.
73 de Brian, VK2GCE.

On Thursday, April 06, 2017 12:57 AM, Dave opined:

They are brought back to the same fuse The ring as a whole is fused for 30A, each (fused) outlet on the ring is rated for 13A. Typically a ring will serve a floor area of up to 100 sq. mtr. per ring, with unlimited sockets in a domestic environment (diversity). For more information: < https://en.wikipedia.org/wiki/Ring_circuit>

Dave



[Non-text portions of this message have been removed]

Re: 7623A power supply low

 

u973 is a ca306
@Jerry,
That's a typo; Officially, it's a CA3045F (156-0065-00), CERDIP package, like a common CA3046, PDIP package. AFAIK, only packages different.

Raymond

Re: 7623A power supply low

Jerry Massengale <jmassen418@...>
 

u973 is a ca3064 that is known to develop very low gain in one of the
sections. this is not detectable with diode checks

jerry

On Wed, Apr 5, 2017 at 8:47 PM, dadhills@... [TekScopes] <
TekScopes@...> wrote:



The Voltages on U973e are strange to say the least. Your readings show the
B-E is (4.36-0.73) = +3.63v and B-C is (4.36-2.35) = +2.01v. Not possible
if Q973e is a functional transistor. Also, where could the +4.36v on the
emitter be coming from if the +5v rail is 0.1v? The only current path is
R970, which presumably is at 0.1v on the opposite end. Unless U973 is
completely toast, in which case it could be leaking through the substrate
or an internal short since the "c" section collector is tied to +15v and
the "b" section collector is tied to +50v, well actually +31v, I seem to
remember.

Measuring the remaining terminals on U973 would be helpful at this point.

Dave

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Re: Type 503 Oscilloscope Issues

 

@Evan,
As such, I only now have gotten time to focus on the scope.
No autofocus on this oldie then?

Seriously, what wonderful condition! Well worth repairing!

Raymond

Re: Type 503 Oscilloscope Issues

Dave Casey
 

Sounds good. There may actually be a problem with D672, and you can do some
easy checks to further verify that. The +12.6V supply is used for the
heaters of the input amplifiers (the first amplification stage your input
signal goes through). While the other tubes are heated with AC from a
transformer winding, these are heated with DC for the sake of reduced
noise. Your scope has two possible configurations:
1. The earlier style where the input tubes are V334 and V434, (two 6DJ8s).
2. The later style where the input tubes are V334, V434, V344, and V444
(four 8393s). The 8393 is a late-to-the-party kind of tube called a
Nuvistor, and it's in a small metal can instead of a big glass bulb.

In either case, the +12.6V supply should still be feeding the heaters of
these tubes.

You might re-check D672 with all two (or four, depending on the above)
tubes removed from their sockets and see if it looks more like the others
than it did in your previous round of measurements.

With those tubes removed, you have also broken the return current path for
the +12.6V supply. This means you can also test the D672 using the ohmmeter
function of your multimeter without having to unsolder it. To do this, with
those particular tubes we're talking about removed, measure the resistance
across D672, then reverse your test leads and repeat the measurement. You
should get two very different measurements. When the positive lead of your
meter is on the "pointy" side of the diode's arrow, you should see an open
circuit (greater than 20M ohm). If you do not, then either the diode is not
a diode anymore, or one of the filtering capacitors after the diode (C652c
and C654c) is bad. Because of the capacitors, you may initially see a very
low resistance measurement that steadily increases until it exceeds the
range of your meter. This is normal and is just your meter charging up
those capacitors.

There is only one other place I see the 12.6V rail being used, and that is
to bias the heaters of the other tubes (also a noise reduction technique).
This is on the power supply schematic next to T601 pins 10 and 11. R605 is
going to do a pretty good job of not letting a fault in that part of the
scope overload the 12.6V supply, and you can get a fairly decent
measurement of R605 in circuit (if anything, it has probably drifted higher
than 47k, which shouldn't hurt anything).

With the test leads reversed (positive lead of the meter on the T620
transformer side of the diode), you should see some finite resistance, even
as high as tens of kilo-ohms (depends on the diode and the meter).

Obviously all this is still to be done with the scope unplugged. (Yes, roll
your eyes, but I'm going to remind you every time. And you should hold the
loose plug in your hand every time before you reach into that chassis; it's
a good habit that can save you from making a careless mistake.) It is also
a good idea to keep track of which tube came from which socket and put them
back like you found them. Mixing them up will affect the calibration of the
instrument (or what's left of it after all these years sitting). If you mix
up the tubes you may or may not be able to tell the difference when the
scope is working again, but it shouldn't make or break operation of the
scope (unless one of them is bad).

While they're removed, it's a good time to check each of those two (or
four) tubes for a shorted filament (heater). A shorted filament would cause
an increased load on the 12.6V supply, possibly causing all the other power
supply problems you're seeing, including the blown fuse.

Regarding GFCI - you can rather inexpensively get an add on GFCI that plugs
into the wall and provides a protected outlet. They are sold at home
improvement/hardware stores. At this point, the power switch wiring is no
longer much of a suspect since that wiring didn't actually burn, but if it
were a problem, a GFCI would trip right away and let you know.


Dave Casey

On Thu, Apr 6, 2017 at 2:58 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



1. For the diodes, those values are from my multimeter in diode testing
mode, but it does not display any units associated with the reading (so I
am assuming it is in volts).

4. C614 gives a resistance of 3.2 ohm, so it would seem that it checks
out.


I also checked the burnt black stuff on the wires, which did peal off with
some isopropanol. It appears to be just melted plastic, and it is not from
the yellow wire (since that was clean underneath). As such, the burning
smell may have just been old plastic and dust from various loose components
that were not cleaned off initially (for example, the rubber casing around
the CRT connector has basically dried and disintegrated at this point).



As for the -3000 V supply to pin 5 on T601, it gave a resistance of ~4.40
M-Ohm (my multimeter reads up to 20 M-Ohm, so it should be accurate).


With the video, the only thing with V659 was that it was flickering on and
off (which is accurate in the video no matter the angle), although it is
difficult to make out the behavior of V620. Again, the issue that I
observed with that was just the blue electron streams around the sides of
the wall, and then the redness at the center of the metal plate in the
tube.


I won't be doing any voltage testing until the new fuses come in, and they
are the correct type (1.25 A, Slo-Blo), so nothing to worry about with the
dangers of higher rated fuses. I do not have any AFCI or GFCI outlets
available unfortunately, so I will just be very careful in the live testing
once I get to that point. However, I will be sure to check what I plan on
doing here before proceeding, since I definitely do not want to fry
anything (or myself for that matter).


- Evan


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[Non-text portions of this message have been removed]

Re: Type 503 Oscilloscope Issues

Evan
 

1. For the diodes, those values are from my multimeter in diode testing mode, but it does not display any units associated with the reading (so I am assuming it is in volts).

4. C614 gives a resistance of 3.2 ohm, so it would seem that it checks out.


I also checked the burnt black stuff on the wires, which did peal off with some isopropanol. It appears to be just melted plastic, and it is not from the yellow wire (since that was clean underneath). As such, the burning smell may have just been old plastic and dust from various loose components that were not cleaned off initially (for example, the rubber casing around the CRT connector has basically dried and disintegrated at this point).



As for the -3000 V supply to pin 5 on T601, it gave a resistance of ~4.40 M-Ohm (my multimeter reads up to 20 M-Ohm, so it should be accurate).


With the video, the only thing with V659 was that it was flickering on and off (which is accurate in the video no matter the angle), although it is difficult to make out the behavior of V620. Again, the issue that I observed with that was just the blue electron streams around the sides of the wall, and then the redness at the center of the metal plate in the tube.


I won't be doing any voltage testing until the new fuses come in, and they are the correct type (1.25 A, Slo-Blo), so nothing to worry about with the dangers of higher rated fuses. I do not have any AFCI or GFCI outlets available unfortunately, so I will just be very careful in the live testing once I get to that point. However, I will be sure to check what I plan on doing here before proceeding, since I definitely do not want to fry anything (or myself for that matter).


- Evan

Re: 7623A power supply low

Roger Evans
 

Replacing U973 with discrete transistors requires getting two emitter leads into pin3 socket so it might be tricky. My 7623A manual shows U973 as a Tektronix part 156-0065-00 in the parts list, but the schematic has an annotation of *CA3046. If the 7623A comes with a 7B53A, which would be the most likely timebase plugin, there should be two CA3046 socketed in the 7B53A, U720 and U744. You could swap one of the CA3046 from the timebase or be more conservative and buy some spares, they are very cheap. (The reason that I know about the CA3046 in the 7B53A is that one had failed in the 7603 that I bought a couple of years ago - my first 7000 series scope!).

Roger

Re: Type 503 Oscilloscope Issues

Dave Casey
 

One last thing - you might go ahead and verify that the black stuff on the
yellow wire is actually stuff that used to be yellow and has burned as
opposed to something else that has landed on that wire (does is scrape off
and reveal undamaged yellow insulation below?). This black stuff was
present in the video you posted the other day. It may have been there the
whole time you've had the scope and have nothing to do with the burning
smell.

I'm also wondering if the problems I thought I saw with V620 and V659 are
misinterpretations of the video. The red color inside V620 may just be a
reflection of the trace rotation knob, and the "flickering" of V659 now
looks more like a result of the changing camera angle. (V692 definitely
shouldn't be doing what it's doing though!)

DC

On Thu, Apr 6, 2017 at 12:02 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hello all,

I feel bad that it has been several days since my last posting.
Unfortunately, my work is at a standstill right now. Over the past weekend
I had focused most of my work on restoring a vintage volt meter (Triplett
630-A), which is now working (and supports up to 6000 V, although I lack
the HV leads, so no -3000 V testing yet). As such, I only now have gotten
time to focus on the scope.

However, when I connected the leads to the ground (chassis) and -100 V
test point, plugged in the scope, and after the brief burning smell,
nothing happened (no lights for the scope, no CRT turning on, no tubes
activating). I discovered that the fuse had blown during my attempt to get
the voltages, but after no luck in going through my fuse stock, I ended up
having to order a set of new ones to come in, so that won't be until next
week earliest.

For the scope, I was still able to check the non-voltage components on the
power circuit. The diodes still check out, with D652 (and others) giving
readings of ~0.65-0.65 on my multimeter. However, only diode D672 gave a
reading of 0.041 on two different multimeters, so I suspect this one is
bad. This one is connected to the +12.6 V circuit.

As for resistors, some also seem to have issues, with R692 (going to V692)
being at 1.4-1.5 ohm, but it is supposed to be 4.3 ohm. I admit I am having
a bit of difficulty in locating R659, so I was unable to confirm if that
one is okay.

Once the fuses come in, I'll let you know how the voltages read out.
However, as for the burning, think it may be coming from the wires leading
to the T601 (see the photo: https://goo.gl/photos/SvfUM7r7w2VY3zsN8
https://goo.gl/photos/SvfUM7r7w2VY3zsN8)


- Evan

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Re: Type 503 Oscilloscope Issues

Dave Casey
 

Evan -

1. When you test a diode, you're trying to verify that it only passes
current in one direction, which means you have to test each diode twice.
Diodes can fail open, where they pass no current, or shorted, where they
pass current in both directions. This is often difficult to discern while
the diodes are in circuit, as there are other paths for the test current to
travel. The measurements you have taken don't tell you much since you've
made them in circuit. It is no surprise that the 12.6V diode, D672 measures
differently as there is a very direct loop through the filaments of V334
and V434 to ground and back through T620. Your readings are also ambiguous
without units attached. Are you just putting the meter in diode test mode
and telling us the number it shows? Is that kOhms? We don't know.

2. R692 is going to measure much lower than 4.3 ohms in circuit because
there is a parallel path for the current through T620 and V692 (that
horizontal line on the schematic right below R692).

3. R659 can be located by tracing back from V659 and forward from L654. It
gets trickier thanks to the wiring harness; I'll admit I haven't found mine
yet.

4. The burned wires in your picture are the primary (mains) side of T601.
The more burned of the two is the Line/Hot from the fuse to an extra tab on
T601 where the wiring changes to the shielded wire running to the power
switch. You might check to verify that C614 (the ceramic disc capacitor
hanging off the bottom of T601) has not shorted. You should see a
resistance of about 3 ohms across C614 while in circuit (scope unplugged,
power switch off, fuse or no fuse). If C614 has failed, it is best replaced
with a modern "X" rated, UL listed capacitor of the same value. If it
hasn't, you have other problems either in or beyond T601. (Has anyone here
who's familiar with the elevated filament short seen it cross to the
primary winding?)

You should repair the burnt wiring before attempting to power the scope
again. The wiring to the power switch (the red wire connected to the burned
wire) and the wiring back from the power switch (the smaller white wire
that runs through the harness with the red wire and is connected to T601
3/4) should be checked for damage also. If the fuse keeps blowing, you
should NOT use a higher rated fuse in an attempt to get more time to test
things - you will only cause more damage. The power switch wiring might be
best tested by using a megger since it is shielded along its path through
the scope.

Have any of your attempts to power the scope been through a AFCI or GFCI
outlet? Did the protection ever trip?

Please be careful and talk through your next steps with us before you do
any more powered testing (you can safely measure the resistance across C614
anytime you like as long as the scope is unplugged). You might also tell us
what resistance you measure between the -3000V supply and the chassis (T601
terminal 5 is a good spot), which should be safe to measure so long as the
scope has been off for awhile (it *should* be safe within a second or two);
resistance should be a few megohms, possibly above the range of your meter
in which case the exact value is not critical. The value is determined by
the resistors along the left hand side of the CRT schematic (R840, 841,
842, 844, 845, 847, 849, 851, 852). If the measurement is lower than a few
megohms, then that filament winding in T601 that we've been worrying about
might be to blame. This is another place where a megger might tell you
something useful.

Don't be too proud to ask questions about anything I've said that you don't
understand; if I'm wrong about anything, the other list members will be
quick to call me on it. We don't want you to learn any of this the hard
way, because you may not survive the lesson.

Dave Casey

On Thu, Apr 6, 2017 at 12:02 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hello all,

I feel bad that it has been several days since my last posting.
Unfortunately, my work is at a standstill right now. Over the past weekend
I had focused most of my work on restoring a vintage volt meter (Triplett
630-A), which is now working (and supports up to 6000 V, although I lack
the HV leads, so no -3000 V testing yet). As such, I only now have gotten
time to focus on the scope.

However, when I connected the leads to the ground (chassis) and -100 V
test point, plugged in the scope, and after the brief burning smell,
nothing happened (no lights for the scope, no CRT turning on, no tubes
activating). I discovered that the fuse had blown during my attempt to get
the voltages, but after no luck in going through my fuse stock, I ended up
having to order a set of new ones to come in, so that won't be until next
week earliest.

For the scope, I was still able to check the non-voltage components on the
power circuit. The diodes still check out, with D652 (and others) giving
readings of ~0.65-0.65 on my multimeter. However, only diode D672 gave a
reading of 0.041 on two different multimeters, so I suspect this one is
bad. This one is connected to the +12.6 V circuit.

As for resistors, some also seem to have issues, with R692 (going to V692)
being at 1.4-1.5 ohm, but it is supposed to be 4.3 ohm. I admit I am having
a bit of difficulty in locating R659, so I was unable to confirm if that
one is okay.

Once the fuses come in, I'll let you know how the voltages read out.
However, as for the burning, think it may be coming from the wires leading
to the T601 (see the photo: https://goo.gl/photos/SvfUM7r7w2VY3zsN8
https://goo.gl/photos/SvfUM7r7w2VY3zsN8)


- Evan

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[Non-text portions of this message have been removed]