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Hi, I was wondering how to remove the older style pull-tabs on the TM500 series plug-ins. These use just a piece of plastic bending, unlike 7000 series plug-ins. Hopefully, they can be removed in a non-destructive manner.

These are on my FG501s, and I need to remove these pull-tabs to remove the faceplate.

Thanks,

-Benjamin

On 2/12/2024 2:00 PM, Mike Dinolfo wrote:

I might be interested in the 453; but can you first clarify what "your area" is, geographically?

The subject line of this thread says "near Madison, WI, USA."

I might be interested in the 453; but can you first clarify what "your
area" is, geographically?

An acquaintance near here says he has some Tektronix gear that used to belong to his deceased father, who formerly worked for Burroughs. He sent me some photos of what he could get to easily, but that only included a Tek 453, a DeVRY Technical Institute scope (sounds like a kit built as part of an electronics correspondence course) and two old analog VOMs, which I can't identify.

I gather that there are some Tek plugins of some kind buried farther out of reach, but I don't know what might be there. I'll keep on him for more info.

The condition is dirty, and otherwise unknown, so the price is likely to be cheap, or less. He would just like to find them a good home.

I will continue to bug him for more info on the other parts, but in the meantime if there's anyone in this area that's interested, let me know. I can send photos and put you in contact with the owner.

Ripple is within spec.

Why did I replace the capacitors?
1. It's relatively simple and cheap to replace them
2. I've had capacitor issues in other equipment. The biggest offender
being the Rifa caps in my other oscilloscope

I did suspect the CRT but given that the scope works in X-Y mode that lead
me down that route.

Why the pre-amp and sweep? This is where the manual lead me through the
troubleshooting so far. It may be the wrong path, but it's a path I can
follow to see where it leads.

Guy,

Thanks for your insights Where I have been focused the last day is to
try and understand why the CLKOUT stays at 25mhz both in the hung and
running fine state. Actually its probably 24mhz due to the 48mhz
oscillator, I think its supposed to be doubled to the log stated 50mhz
(48??) as one of the ending steps of the boot sequence. There may be a
PLL lock problem or the clock setup fails for some reason, I really do not
know for sure at this point that the 50mhz applies to the MPC860 core and
the external CLKOUT remains at 25 as I am reaching out for conformation.
Personally I think the external clock need to be 50mhz as 25 is really slow
for what they have here, all that said it seems to run fine at 25mhz and I
have not seen any issues after a successful boot.

Temperature testing is a bit of a challenge and I have spent a bit of
time on it since the failure mode really mimics a sensitivity to being
warm or cold but nothing I have tried will force it to ether the fail or
pass state. I have been heating or cooling primarily in sections of the
board from larger areas down to the device level. I have done the whole
board and supplies but intentionally limited it in the acquisition section.
I use a large and small heat gun and have used most of a large can of
freeze spray, I track the temperature with a handheld FLlR IR camera that
has resolution down to the SMD passives sizes and shows the temp very
accurately.. Temp wise my upper limit has been ~160f to -40f or so for
some spot areas like the DRAM. I will work up a plan to try to temp cycle
the whole thing as you suggested, definitely worth a try.

When the unit is in the hung state I did see the refresh but did not
measure the period and will put that on the list. After all time spent
with this if I could offer some off the wall perception of the problem that
may or may not make any sense: Its seems like its a 'charge' or maybe a
given 'impedance' somewhere and their value shifts in one direction while
its on and the other direction while it is off -very- slowly. This 'charge'
or 'impedance' change over time is not affected by temperature very much
but when the value crosses some point it will cause it to fail.

Best Regards,
Mike

If I'm not mistaken, there's an "odd" resistor with something like 90.9 labeled
on it. I'll have to get that back out and see exactly what value it is. I got
these resistors from an estate sale and it looks like they've never been used
for anything.

Yes, it's just to get the HV set on the cathode of the CRT. Technically, it's
supposed to be within 1%. I have a Triplett 630-NA that has a 6000VDC range
that I've used as a rough check but I want to get this much closer than that.

Thanks for the good info.
Barry - N4BUQ

----- Original Message -----

From: "edbreya=yahoo com" <edbreya@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, February 8, 2024 1:52:17 PM
Subject: Re: [TekScopes] Method to measure HV

Barry wrote "I presume that because the probe uses a 75M and a 75k in series and
the 10M voltmeter is across the 75k, the 10M has minimal effect on the
divider's ratio. Is that correct?"

It depends on what you mean by "minimal effect." In reality, for a commercial
1,000X probe at 75 megs input, the "75 k" termination resistor is likely 75.643
k, which is about right to attain nearly the ideal value of 75.075...k when the
10 megs DMM input R is paralleled. That's why Jean-Paul mentioned being sure of
that 10 meg value.

Your 10X probe deal should work just fine, but be aware of the dependence on the
DMM's input R, and whether it's connected. If you get into a situation where
the 90 megs of R are left dangling out there, it's a current source backed by 3
kV, so can run up to 33 uA into whatever it could contact. It can't hurt you,
but could damage certain parts if contacted. If the DMM is always securely
connected, it's still a current source, but limited to 300 V. The main thing is
to keep it wrapped up to avoid any mishaps. The exact same thing can happen
with any HV probe if it's ground connection is forgotten or inadvertently lost,
so always be sure it's secure.

You can also opt for a higher divide ratio like 100 or 1,000X, which is what
most HV probes do, to get more comfortable measuring voltage, It's quite easy
to adapt any high-meg resistance into a nice HV divider. The higher the divide
ratio, the more flexibility you have in hitting the values right and handling
multiple load values. For instance, you could go with 100X instead of 10X, and
be able to drive a 10 meg or 1 meg input. With the same 90 megs of inlet R,
you'd want the bottom R to be 90 M/99, so 909.09... k. This can be conveniently
made with a 1 M termination paralleled with the DMM's 10 M input R, or, a 10 M
termination with a DMM (or scope) input R of 1 meg. These are all idealized
values, of course. The actual ones have to be worked out. It's most important
to know the tempco, voltco and actual value of the inlet R - everything else
can be worked out to accommodate it.

Anyway, since your application seems simple enough here - just checking a scope
one time (right?), and not needing extreme precision, your 10X thing is already
the way to go. It's good to consider options too, if more of such needs are
expected.

Ed