On Apr 18, 4:56*pm, "Andrew Holme" wrote:
"Markus Wolfgart" wrote in message

...



Dear OM's

I'm looking for some help concerning a defective driver pcb for a
yig oscillator inside the mentioned device above.

see link: (http://www.mikrocontroller.net/topic/215840#2149959)

I'm looking for the proper value of the destroyed resistor ( 50 ohm) in
the lower corner as well as for the value of the capacitor.

Have any of you a link to the service schematic of the mentioned driver,
or could send me a copy of it.

Any help would be appreciated.

vy73

Markus
alias
DL8MBY

I agree with K7ITM that tants have a habit of burning out like the one in
your photo. *And I agree it looks like the tant and series R or L are just
filtering a power supply coming onto the board.

From the photos, it looks like the square pad of the blown tant is connected
to a ground plane inside the board. *After removing the cap, you could buzz
it out to check. *But I think I see a + adjacent to the square pad on the
top copper in your 01k photo. *I wonder if there is an error in the PCB
layout or the schematic. *You might want to check if pin 8 is really +15V
or -15V by measuring the voltage on the unplugged cable.

Yeah, I kind of wondered about the connections to the cap too. Since
we don't have the board, it's hard to tell. It does look like a 4-
layer board, and in that case the interior layers may be ground and
power (with the power possibly split between +15 and -15, or
such...). I fully agree with Andrew: ohm/buzz out the connections to
reverse-engineer as much of the schematic as you need. It's a pretty
simple board, and shouldn't be difficult. If there's a code on the
two transistors, I can probably tell you what they are (assuming they
aren't labeled 2N3904 or whatever). Typical would be 4-nnn (for an
NPN) or 3-nnn (for a PNP) -- abbreviations for the full HP part
number, which would be 1854-xxxx or 1853-xxxx. The full numbers were
a bit hard to put on small parts back then.

Cheers,
Tom