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Hello!


I've troubleshot my beloved 485, to the point I have to just let go -- I must send it to my scrap heap (spare parts shed) -- with the help of the service manual, I traced the problem to the -3KV cathode supply; once I got into it and tore the scope apart to get to the "transformer board" (whoa what a mess) -- I realized I might not have the time/patience to get it back together, even if I could test the HV diodes, multiplier (for anode) etc, "pot" my own multiplier, find a replacement, etc....


How much time should a person spend reviving a 485 when you can find them on craigslist for $400 "calibrated"?


I used a digital scope (Rigol 50mhz) to easily capture that 485 startup "balancing node" thingy, where actually the Rigol proved it's $300 value by saving me a lot of headaches to capture that 20ms period after power up and after the 6ms initial delay. It asked that I bend a pin on one of those "comb" connectors, and if the scope powered up (sans HV), it was the cathode supply short circuit (then I didn't find any obvious problem in the HV in continuity checks I assume my DVM doesn't put enough volts out to cause forward conduction).


So, if anyone has any "encouragement" on what I should / can do with the 485, that's appeareciated but by default I am "beyond mourning" -- I'll just leave it for another day or when I need to steal parts to make a Ham radio.


Yesterday I acquired a 454; it actually has one trace working (rough test) and the other trace doesn't appear. Anyone know if this is a "known or common issue"? SN 60101XX series, if that helps. I hope to avoid another half day wasted ending in frustration as I don't have the parts nor experience to know what parts to substitute, where to get oddities that won't break my bank, etc.


I've not mustered the courage to crack the 454 open, I bought it from a fellow HAM who knows what he's doing, I don't think repair attempts have been like made.


I have one thread of me wanting a Tek analog scope back on my bench, I know the Rigol has it's own plusses/minuses, but I have only so many years to spin away on fixing stuff so I can do what I want to do ultimately (building ham equipment and actually using it).


Thank you kindly!!!!!!!


Ronan/KB6NHQ
Meadow Vista, CA

Ronan:

There is a great amount of satisfaction in successfully repairing high-tech
instrumentation. Some of my old equipment out-performs the latest
offerings. Often it is worth the trouble to do the repairs. Try not to
think of the disappointments.

Gary
On Dec 1, 2014 6:31 PM, "dudelucky583@... [TekScopes]" <
TekScopes@...> wrote:

Hello!


I've troubleshot my beloved 485, to the point I have to just let go -- I
must send it to my scrap heap (spare parts shed) -- with the help of the
service manual, I traced the problem to the -3KV cathode supply; once I got
into it and tore the scope apart to get to the "transformer board" (whoa
what a mess) -- I realized I might not have the time/patience to get it
back together, even if I could test the HV diodes, multiplier (for anode)
etc, "pot" my own multiplier, find a replacement, etc....


How much time should a person spend reviving a 485 when you can find them
on craigslist for $400 "calibrated"?


I used a digital scope (Rigol 50mhz) to easily capture that 485 startup
"balancing node" thingy, where actually the Rigol proved it's $300 value by
saving me a lot of headaches to capture that 20ms period after power up and
after the 6ms initial delay. It asked that I bend a pin on one of those
"comb" connectors, and if the scope powered up (sans HV), it was the
cathode supply short circuit (then I didn't find any obvious problem in the
HV in continuity checks I assume my DVM doesn't put enough volts out to
cause forward conduction).


So, if anyone has any "encouragement" on what I should / can do with the
485, that's appeareciated but by default I am "beyond mourning" -- I'll
just leave it for another day or when I need to steal parts to make a Ham
radio.


Yesterday I acquired a 454; it actually has one trace working (rough test)
and the other trace doesn't appear. Anyone know if this is a "known or
common issue"? SN 60101XX series, if that helps. I hope to avoid another
half day wasted ending in frustration as I don't have the parts nor
experience to know what parts to substitute, where to get oddities that
won't break my bank, etc.


I've not mustered the courage to crack the 454 open, I bought it from a
fellow HAM who knows what he's doing, I don't think repair attempts have
been like made.


I have one thread of me wanting a Tek analog scope back on my bench, I
know the Rigol has it's own plusses/minuses, but I have only so many years
to spin away on fixing stuff so I can do what I want to do ultimately
(building ham equipment and actually using it).


Thank you kindly!!!!!!!


Ronan/KB6NHQ
Meadow Vista, CA

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

Thanks for the encouragement - I agree generally, it is just that my primary focus is to use test equipment in service/design,rather than to spend inordinate time repairing it. Having said that I know I would love doing anything I felt was a challenge I could overcome!

If I could have found someone -- an expert on the 485 to take it on for a reasonable fee, I wouldn't mind so much compensating said person... however I DID get immense satisfaction I followed the Tek manual to isolate the problem; without that I would have given up a long time ago!


With the 454, it's no match for the 485, but at least it's a Tek analog scope with no apparent HV issue (yet).

Cheers,
Ronan/KB6NHQ

Ronan,

I think you will find the 454 much easier to work on than a 485. The cover comes off easily, and many (not all) circuits can be accessed conveniently.

--John Gord

Maybe it looks more promising if you know that the 454 contains no Tek-made ICs. See also


Finding the fault in the second channel must be much easier than finding the fault in the HV unit. The fault can't be that far from the "entrance" and you can compare voltages/signals of both chanels. With some luck you only have to clean a switch!

Albert

The 454 is old enough that contact oxidation is a problem. The transistors are
socketed and odd problems like a missing channel may be due to a poor contact.
I've fixed more than one scope of that vintage simply be reseating the transistors.

I have a 454 on my desk that I refurbed earlier this year. I really like being able
to read the controls without having to dig up a magnifier; it's my scope of choice
for when I need a quick look at something.

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