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hp5326a timer-counter

Hi all,

I have found an old hp5326a that I would like to repair because I like to restore old equipment. Almost everything works apart input A. The problem seems to stay on the input board p/n 05327-60034, because even swapping the two boards connected to it to handle the triggering for A and B, the problem remains on A. By comparing channels A and B, I see that in the working channel the trigger level pot changes a voltage on the connector going to the respective trigger board, while this doesn't happen on the other channel. The corresponding line goes to a metal can, 6 pin chip marked 5-334. Unfortunately I couldn't find the schematic on the net (for free or at least cheaper respect to what I payed the instrument...). Neither I was able to find any info about the chip: I tried something like 1855-0344 but I later discovered that, in hp numbering, xxx5 is never used for ICs.

I wonder if someone can help... (my real mail is on the web page)

Regards,

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

Reply to
Caesar Valenti

formatting link

scroll down to 1855-0334

but beware, 24$/pice (Canadian $)

Jorgen dj0ud

HTH,

Jorgen

Reply to
Jorgen Lund-Nielsen

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/
Reply to
RoV

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