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Tektronix TDS684A

Thomas Dodge
 

Hi,
I emailed about this before. I have a Tektronix TDS 684A scope, and it is
in very good condition, and it was almost working, but now it is not. I
bought it from a surplus place, and I had seen it every time I came into
the place. When I took it home the first time, and powered it on, it didn't
do anything. But after a while, the panel lights came on, and it did run
the self test. When I powered it on recently, the panel lights power on,
but no self test at all. I want to know how to fix this. I do have the
manual, but I would like to work together with someone who is local in my
area who is more experienced than I am. I could just send it off to be
repaired, but that would be no fun for me. I have a couple other Tektronix
scopes that are not working too. Does anyone know who is around my area? I
am in California, in the San Gabriel Valley area in Glendora. I want to
learn how to fix these when problems come up. I am well aware of the high
voltage that is present here, so that's why I am asking. Any help is
appreciated. Thanks very much.

Thomas Dodge
Harvey White
 

I'm not in California, in fact, about as far away in the US as you can get from there.

However, I've worked a bit on TDSS540 scopes, and I have a TDS640 as well.

Things to know:

1) the only high voltage is in two places, inside the power supply (should be more or less shielded), and inside the monitor (should be shielded as well).

Most other voltages are at the class 2 (less than 24 or so volts) level.

2) these power supplies are similar, but not as well documented as you'd like.  It sounds a bit like a power supply problem until you check all the voltages and know it isn't.

3) some scopes of the era (and type) have a known capacitor problem.  Try inspecting each capacitor on the boards (not the PS board, that's another animal) for dull looking leads or any sign of leakage.  I'd suggest that you look for threads about the TDS series which will cover various issues about some capacitors. There's a self test capability (at least in mine) on the CPU board which runs through a number of tests, with the pass/fail indication being on a 7 segment readout.  It should hang (with the right switch settings) on a failing test.  That'll give you an idea if the CPU is failing.

Further than this, I can't help too much, there are people here who have done a lot more work on these than I have.

Harvey

On 1/11/2021 7:19 PM, Thomas Dodge wrote:
Hi,
I emailed about this before. I have a Tektronix TDS 684A scope, and it is
in very good condition, and it was almost working, but now it is not. I
bought it from a surplus place, and I had seen it every time I came into
the place. When I took it home the first time, and powered it on, it didn't
do anything. But after a while, the panel lights came on, and it did run
the self test. When I powered it on recently, the panel lights power on,
but no self test at all. I want to know how to fix this. I do have the
manual, but I would like to work together with someone who is local in my
area who is more experienced than I am. I could just send it off to be
repaired, but that would be no fun for me. I have a couple other Tektronix
scopes that are not working too. Does anyone know who is around my area? I
am in California, in the San Gabriel Valley area in Glendora. I want to
learn how to fix these when problems come up. I am well aware of the high
voltage that is present here, so that's why I am asking. Any help is
appreciated. Thanks very much.

Thomas Dodge
Thomas Dodge
 

Thanks Harvey,
I just read your email. The self test did actually work one, but only
after cycling the power on and off a few times. When I powered it on the
other day, the panel lights came on, but I didn't hear the relays activate,
and no self test ran. I think the first time i powered in on, and cycled it
on and off a few times, it was working ok. Thanks again for your help. It
really is a great scope.

Tom Dodge

On Mon, Jan 11, 2021 at 4:56 PM Harvey White <madyn@dragonworks.info> wrote:

I'm not in California, in fact, about as far away in the US as you can
get from there.

However, I've worked a bit on TDSS540 scopes, and I have a TDS640 as well.

Things to know:

1) the only high voltage is in two places, inside the power supply
(should be more or less shielded), and inside the monitor (should be
shielded as well).

Most other voltages are at the class 2 (less than 24 or so volts) level.

2) these power supplies are similar, but not as well documented as you'd
like. It sounds a bit like a power supply problem until you check all
the voltages and know it isn't.

3) some scopes of the era (and type) have a known capacitor problem.
Try inspecting each capacitor on the boards (not the PS board, that's
another animal) for dull looking leads or any sign of leakage. I'd
suggest that you look for threads about the TDS series which will cover
various issues about some capacitors. There's a self test capability (at
least in mine) on the CPU board which runs through a number of tests,
with the pass/fail indication being on a 7 segment readout. It should
hang (with the right switch settings) on a failing test. That'll give
you an idea if the CPU is failing.

Further than this, I can't help too much, there are people here who have
done a lot more work on these than I have.

Harvey


On 1/11/2021 7:19 PM, Thomas Dodge wrote:
Hi,
I emailed about this before. I have a Tektronix TDS 684A scope, and it
is
in very good condition, and it was almost working, but now it is not. I
bought it from a surplus place, and I had seen it every time I came into
the place. When I took it home the first time, and powered it on, it
didn't
do anything. But after a while, the panel lights came on, and it did run
the self test. When I powered it on recently, the panel lights power on,
but no self test at all. I want to know how to fix this. I do have the
manual, but I would like to work together with someone who is local in my
area who is more experienced than I am. I could just send it off to be
repaired, but that would be no fun for me. I have a couple other
Tektronix
scopes that are not working too. Does anyone know who is around my area?
I
am in California, in the San Gabriel Valley area in Glendora. I want to
learn how to fix these when problems come up. I am well aware of the high
voltage that is present here, so that's why I am asking. Any help is
appreciated. Thanks very much.

Thomas Dodge
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