Tektronix 7B92 auto trigger not working

[Andy Cuffe]

I bought this on ebay recently for my 7603. It's 99% working, but
auto trigger mode doesn't work properly. It behaves exactly the same
as normal trigger mode. It triggers fine when there's an input, but
the trace disappears when there's no signal. I've tried it in 2 other
scopes with the same symptoms. I've confirmed that the switch is
working and traced it back to the 155-0049-01 IC. I also swapped the
155-0049-01 with one from a parts scope.

Has anyone seen anything like this before?
Andy Cuffe

[email protected] <-- Use this email address first

[email protected]

 

[Jim Yanik]

I bought this on ebay recently for my 7603. It's 99% working, but
auto trigger mode doesn't work properly. It behaves exactly the same
as normal trigger mode. It triggers fine when there's an input, but
the trace disappears when there's no signal. I've tried it in 2 other
scopes with the same symptoms. I've confirmed that the switch is
working and traced it back to the 155-0049-01 IC. I also swapped the
155-0049-01 with one from a parts scope.

Has anyone seen anything like this before?
Andy Cuffe

[email protected] <-- Use this email address first

[email protected]

If you have a 155-0049-02,try that.It replaced the earlier -01 version.
IIRC,there were problems with the -01.You may have some other
problem,though.There were a bunch of trigger mods for this item,IIRC,but
finding documentation on them will be near impossible,unless you know
someone with the 7B92 microfiche.

The 7B92(or A version) is a bit fast for the 7603.Don't rely on the fastest
sweep speeds accuracy or linearity.And the 7603 delay line is probably too
long for the 92.(Might not see leading edge of sweep)