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All SMD caps replaced, board cleaned and inspected, via's reflowed if showing corrosion signs. Still getting trigComparatorTest FAIL, ERROR ID 151 diagnostic test failure trigComparatorTest, TRIGA status after trigger: exp = 1, act =0. ** alpha trigger (XTRIG), on the RS232 Debug port.
This tells me that there is still an open via somewhere. Since schematics appear to be un-obtanium, I am wondering if anybody with experience on these scopes can at least identify the part of the ACQ board I should look at closer under the microscope. What chips handle the triggering? should be close to the EXT trigger BNC connection on the PC, Yes? Only reason I am fooling around with repairs on this "Antique" (Not so antique as my 511A though) is for the challenge. It has become a big one. It would be great if someone, ex-Tek repair tech, had the schematics on these things, but I am not holding my breath.

The TDS520 component level service manual is available, not sure if it
applies to the 420.
Radu.

On Wed, Jan 15, 2025, 9:36 AM Tim Wright via groups.io <al7ds=
[email protected]> wrote:

All SMD caps replaced, board cleaned and inspected, via's reflowed if
showing corrosion signs. Still getting trigComparatorTest FAIL, ERROR ID
151 diagnostic test failure trigComparatorTest, TRIGA status after trigger:
exp = 1, act =0. ** alpha trigger (XTRIG), on the RS232 Debug port.
This tells me that there is still an open via somewhere. Since schematics
appear to be un-obtanium, I am wondering if anybody with experience on
these scopes can at least identify the part of the ACQ board I should look
at closer under the microscope. What chips handle the triggering? should
be close to the EXT trigger BNC connection on the PC, Yes? Only reason I
am fooling around with repairs on this "Antique" (Not so antique as my 511A
though) is for the challenge. It has become a big one. It would be great
if someone, ex-Tek repair tech, had the schematics on these things, but I
am not holding my breath.

Just checked, and it does not. Different ACQ board altogether. I have a 540, and it is similar to that. Makes sense, same series.

Bummer. It was worth trying.

On Wed, Jan 15, 2025, 11:02 AM Tim Wright via groups.io <al7ds=
[email protected]> wrote:

Just checked, and it does not. Different ACQ board altogether. I have a
540, and it is similar to that. Makes sense, same series.

I have been working on getting the schematics for the TDS 420/460 converted
from production engineering schematics to a form which can be used without
trying to create a manual. I have no background in manual writing, just a
technical background working at Tektronix for about 30 years. I was able
to obtain the drawings from one of the engineers who designed the TDS
series, now passed on. I tried to post on TekWiki via Kurt but I am not
savvy enough to figure out the posting process. So, I have placed the
schematics on my personal ISP site for the time being.



I had sent a couple of the trigger related schematics to Tim in hopes it
would help him find his problem. Kurt at TekWiki has also been informed of
the existence of the schematics.

With the exception of the power supply, I believe the schematics to be
accurate. The power supply information is from Lecroy and has been used
with success but may not be 100% accurate.

Best regards,

Ferrous Steinka

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