mike wrote in :

Artem Belevich wrote:
Hi,

I've got my hands on a used TDS540 in hopes that at least once channel
would work. No luck.

The box comes up with two self-tests failures :
FAIL ++ Acquisition
FAIL ++ Attn/Acq interface

After that, channels 1 and 2 show nothing.
Channels 3 and 4 show 'saw' pattern when there's no input signal
applied. If I connect it to the probe compensation signal I can see
sum of square wave pattern and the 'saw'.

I've followed Tektronix' troubleshooting chart and it looks like
acquisition module A10 is probably bad.

I wonder if anyone here had to deal with the similar issue before.
Looking at the ebay, I've noticed that quite a few TDS* scopes sold
there had failed acuisition and/or attenuation modules. Looks like it
must be a fairly common issue. Does anybody know what are the most
common failures for the tds5xx family scopes?

Thanks,
Artem


Here's what I did to fix mine.
Locate all the silver electolytic caps.
Remove them ALL. Yes, there are over a hundred of them.
They leak and make the board conductive. You must replace
ALL of them.

Wash the boards in simple green then isopropyl alcohol.
Put a .1 1206 SMT cap where each electrolytic was.
Bridge the appropriate value aluminum electrolytic across
each .1.

This made most of the error messages go away.

Washed the boards again in simple green then alcohol.
Scrub with a stiff toothbrush.

This made some more errors go away.

Washed the boards a third time with simple green followed
by alcohol. Scrubbed HARDER with the stiff toothbrush.

Now works great.
Fixed two of them this way.
On the second one, I tried one board at a time. Had to change
ALL the caps on ALL the boards to get it to work.
mike



For better cleaning,try running the PCB through your automatic dishwasher
using Calgonite (leave the dishwasher's drying heat OFF) and dry in a
commercial drying oven or rig up a hot box and a whisper fan or two to pull
air out of the box.You don't want to exceed 150 degF in the box.It should
dry for about 3 days.

--
Jim Yanik
jyanik-at-kua.net