Re: 577 repair


Ouch! no I didn't remember, and yes I so sympathise - been there, smelt the
magic smoke.


-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 16 March 2016 10:35
To: TekScopes@...
Subject: [TekScopes] 577 repair

Some of you might remember that a year or so ago I blew up my workhorse
curve tracer. Shorted tant somewhere, pulled power supply to test which
rail had died, and then after repair, reconnected the supply - with one of
the connectors one pin out. Smoke came out. I was really miserable at my
stupidity, and parked the unit.

Anyway I eventually decided to find out what was dead. The only two
transistors that were dead were two dual FET's, where the gate was resistive
on three of the four FETs. 2N3958, which fortunately Linear Systems have
remanufactured. Two 741's crispy and easy to replace.

As a precaution I'm replacing the op-amps and logic. The only difficult one
is a long-obsolete 7454
- basically four dual input AND's into a NOR (and confusingly the LS part is
not a direct equivalent!); I thought about dusting off my Boolean and
stitching together currently available logic to synthesise the part (I did
that in my HP counter), but in the end just bought the part from eBay.
Anyway all parts are now ordered, so short of collateral damage to diodes
and passives I'm keeping my fingers crossed.

I'll let y'all know how it goes.

Posted by: "Craig Sawyers" <c.sawyers@...>


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