You need to scope the output of the DAC / input to the S/H buffers to
check if the DAC is working. You should see a waveform that looks
like a strange-bargraph (or S/H LFO).

My HS3140C blew and I searched-- the only replacement was from a
military supplier and cost something like $150 or $175. I think I
blew it by messing up the power supply sequence while troubleshooting
the power supply which is similar to what you did...

I ended up using the analog devices AN7538 DAC ($15) which has the
similar specifications but a different pinout. It wasn't hard to
make an adapter using a stack of DIP sockets. Datasheets for both
parts are online. You will also need to set the null-offset per the
service manual when you are finished.

If that seems beyond your technical abilities, send me an email-- I
can have a AN7538->HS3140C socket adapter PCB built for you for $75
(including all parts) or $40 for just a PCB.

Thanks,
Ben

> I'm suspecting, at this point a blown DAC:
>
> A)
> What I can do to be sure that DAC is working (or not working) ?
>
> B)
> Do you know of any DAC HS3140C reseller ?
>
> thank you for your time
>
> AT