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 Post subject: another hp3455a
PostPosted: Nov Sun 17, 2019 12:55 pm 
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Joined: Nov Sun 17, 2019 10:53 am
Posts: 2
gents,

Time for a bit of a puzzler on the power section of an hp3455a.

One came into my life with a smelly and crispy trace by the transformer, both sides of the board. Symptom was a blown fuse. On opening up I noted slight trace damage on the top and bottom. The good news is the trace isn't open as tested by a DMM.

A quick search through the service manual directs attention to the power supply breakdown diodes listing A10CR64 and 66 diodes and checking that the power supply is appropriately set (120 vac / 60 hz correct). The parts listing in the manual does identify the characteristics of the diode as a zener rated as follows: 47.5 v, 5%, do-15 (case), Pd = 1 w, Tc= +0.081%. This diode is available I'll bet but I'm also considering a junk box substitute, if it is indeed the problem. I just wonder if a tantalum failure would lead to a hot pcb trace also, as I understand they are typically what fails on the power rail.

Prior to removing a diode to check it however, I looked for a drawing of the board and the scans of the manual online are awful at best. All the board power / digital drawing pages I found are illegible- and fully compliant with murphy's law.

I should mention that getting on here is long overdue on my part as I've been in and out of the hobby since the nineties. Things like school got in and out of the way in the meantime.

raf
n9sxf


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62A58D10-9B0C-4B3E-B71A-514A8EE55C61.jpeg
62A58D10-9B0C-4B3E-B71A-514A8EE55C61.jpeg [ 456.89 KiB | Viewed 115 times ]
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