Well, the buyer has turned uncooperative, said something about just needing a scope to make some measurements on a current project, and has formally requested a return thru eBay. So it looks like I'm out about $120 worth of shipping, and will have a go at fixing the relays when it gets back here. Can anyone guide me as to what type relays, and how many, I need to be looking at? I have the service manual, but they don't seem to drill down to that level of detail. Also, is this a typical contact oxidation problem, that I might be able to clear by repeatedly cycling those relays? What's the best way to tackle this one?
Steve Hendrix
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At 2021-02-28 01:06 PM, EricJ via groups.io wrote:
I will agree with Siggi on this one as far as one or more of those relays
being the likely cause. One of my TDS scopes had the same problem.
Replacing the relays he mentioned solved it. And yes he'll need to be
careful, the hybrid boards are made of pretty thin ceramic.
--Eric
On Sun, Feb 28, 2021, 9:19 AM Siggi <siggi@...> wrote:
Hey Steve,
The classic fault that causes SPC on these scopes is that the signal relays
on the input attenuator hybrids develop high resistance. They are used to
shunt in the internally generated calibration signal that's used for the
signal path compensation.
I replaced a few of those relays on my TDS784D, which cleared the problem.
The relays were readily available at the time, and I could readily measure
which relays were bad by a simple resistance measurement over the NC
terminals. Clipping the old relays out and soldering on the ceramic hybrid
was a little bit nerve wracking, but definitely very doable.
Siggi
On Sun, Feb 28, 2021 at 9:16 AM Steve Hendrix <SteveHx@...>
wrote:
A year or so ago I bought a TDS784C that seemed to be in pristine
condition except for a missing left rear foot. It powered up and
worked perfectly on every signal I tried it on. I found that I rarely
if ever had an actual need for its high bandwidth (1GHz) and I had
other scopes that met my needs with less bench space, so I sold it on
eBay.
The buyer has been very polite and cooperative, but requests help
with finding a replacement foot, and also reports that he ran a
Signal Path Compensation which reported an error:
"A compensation error has occurred. Examine the error log and note
the message. Then refer this oscilloscope to a qualified service
technician for repair. It is possible to proceed by pressing Clear
Menu. The oscilloscope, however, may not perform according to
specifications."
According to the error log, this error has been present since 2007,
over a decade before i got hold of it.
Can anyone here offer suggestions?
Steve Hendrix
