On Sun, Mar 21, 2021 at 01:26 PM, Steve Nossen wrote:
Measured the transistors and Q213 measures 30 ohms from C to E and E to C on
my SImpson 260. Much higher on a DVM but the same in both directions. Seems
leaky to me. Q203 measured more like a diode, conducts in one direction.
Q213 pins are connected to GND and +5V rails with very low value resistors, so
I would be suspicious of any in-circuit resistance measurements.
A non-invasive test of the basic health of these transistors is to
check the operating point voltages of Q203, Q213 and Q217, and compare
them against the expected values provided in schematic <1>. This check
should not need a signal applied to A20/B20, so the plug-in can be operated
in the vertical compartment for ease of access. (Unless, of course, you are
one of the luck few who have a nice 7000 plug-in extender.)
Also, did you remember to clean all attenuator cam switch contacts with
isopropyl alcohol? This would be the first order of business before
attacking the plug-in with a soldering iron.
dan
