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From the Millenia specs:
"(Bipolar 15 VDC to Bipolar 25 VDC Max Recommended)"

I remember that in the Toshiba datasheets for the Fets used in the Millenia DOA the maximum voltage for 2SJ74 is 25V. So it is possible that bipolar 28V is too much for them.

chrissugar

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In the posted pics there is no +28V and +input. They are all with minus.

[quote author="drpat"]Does anybody have the correct pin-out for the HS1050 to double check my work against?
[/quote]
So you are not 100% sure about the pins of the 1050? Those notations on the PCB are yours or were original?
Try first to measure the +/-V pins, identify the GND pin and then try to identify the out, +in and -in by comparing the PCB with the schematic from Fabio's page.

chrissugar

There is one more thing I don't understand.
I looked at you first picture,with both opamps, and at the schematic.
In the schem there is a Hs1000 or 1020 for the differential input circuit and a HS1050 for the out amp. In your picture from what I identified it looks like the input buffer is 1050 and the output amp was changed to 990. Am I right? If I am you should probably put the 1050 in the out amps place and the 990 at the input.
You should also try to reduce the 28V to something like 24 or 25. You can do it just for this experiment by connecting 5 diodes in series at the + side and 5 at the minus. At least you will see if the too high voltage is the problem or something else.

chrissugar

Just a thought...

It may help to connect the suspect DOA's up on a breadboard away from the main unit to check for "op-amp function". This way you can verify that they actually are dead and that it's not something down-the-line in the unit.

Just a simple gain stage will do, and then apply a signal.

Mark

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Yes, the best idea is to test the opamp on breadboard. configure the test setup with a feedback network that will provide let's 20 dB gain to avoid any possible stability problems at low gain. Also use som decoupling caps close to the DOA.
I have the feeling that the 990 is dead. :sad:

chrissugar

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Thanks, Patrick!

That sontec opamp, that you obviously had to replace - don't you think that it deserves a good ol' de-potting, now that it's retired?

Some realgood knowledge could probably be extracted..

:razz:

Jakob E.

That sontec opamp, that you obviously had to replace--don't you think that it deserves a good ol' de-potting, now that it's retired?

Click to expand...

Who could disagree here?

Send it to Switzerland if you don't need it anymore (seriously).

Samuel

Hey Patrick, arent you going to tell us how it sounds now? :razz:
:thumb:

M@

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:grin:
:green:

M@

Hey Matt,

how was that 18 hour flight back home from AES???

Well, it occured to me after about 12 hours that being stuck on a 747 for the rest of eternity would be my personal idea of hell.
:evil:
We had to stop in Hawaii to let off a sick passenger so that turned an unbearable 14 hour flight into a physically damaging 18 hour nightmare. Could have been worse though I guess - we could have crashed.
:roll:
:wink:


M@

Any news about the reversing process for this discrete?

chrissugar