Re: hp5326a timer-counter

You had the right idea. The p/n is 1855-0334 (not 0344). It is not an
IC, but rather a dual FET, hence the 6 pins. I think the manufacturer is
Siliconix.
Unfortunately, I could not (easily) find a cross-reference, so I do not
know much about it....but there are a couple dozen hits in Google....try
that.
cv

http://www.sphere.bc.ca/test/hp-parts/hpparts4.html

scroll down to 1855-0334

Thank you Caesar and Jorgen.
Once I understood it was a dual FET, I tried to take some measurements with
the scope to fix the source of the problem. But it proved impossible,
because the board is located behind the front panel, with other four boards
orthogonally placed behind it (two of them, the trigger boards, are inserted
in this one and also on the bottom backplane. So I decided to try to remove
the front panel to access the back of the board. Finally I was ready, in a
very temporary setup (potentiometers and commutators hanging around,
protected with plastic bags from shorts...). I turned the instrument on and
to my surprise it worked. I was happy, but a bit disappointed for the time
required to dismount it!
I finally realized that the trigger level pot on input channel A (the failed
one) did non work when its axis was pressed; probably I accidentally put it
to work by pulling it to remove the knob! Unfortunately, it is quite a
special kind of pot, but I think I can leave it as it is now that I know the
trick.
Fortunately, once remounted, the instrument kept on working. It reads up to
85MHz, not bad for being rated 50MHz.
In any case, I hope I will find the service manual sooner or later.

Regards,
Roberto

--
RoV - IW3IPD
http://digilander.libero.it/rvise/


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