开云体育

I hate to be stupid about this, but my HP-140B (serial 1119A00489) doesn’t have a DS101, only a DS401 (the Power ON lamp). Might you be referring to one of the plug-ins??

Jeremy?

N6WFO?

On Sun, Apr 14, 2024 at 3:14?PM n4buq via <n4buq=[email protected]> wrote:

I am still unable to get DS101 to turn on in my HP-140B.? I can ground Q109's base through a resistor and force the lamp to turn on.? I can place a 1K resistor in parallel with R137 and also force the lamp to turn on; however, nothing else works.? I thought that the neon might have aged to the point where there isn't sufficient striking voltage for it but since it will turn on with these methods, that doesn't seem to be case(?).

Setting the unit up as described in the manual for voltage tests, I get the following:

-100V F(B): -99.9V

Q109

Emitter: -9.35V

Base: -8.78V

Collector: -0.33V

Q110

Emitter: -8.01V

Base: -8.11V

Collector: -3.7V

Given those values, it would appear (at least to me) that the lamp should turn on but it doesn't.

As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and connected a battery, resistor, and LED between GND and the collector of Q109.? This works just as it should (i.e. the LED turns on when the sweep is triggered, turns off at the end of the sweep, and repeats that).

Is it possible that Q109 is not able to conduct enough current to turn DS101 on but enough to make the LED work?? That seems unlikely but, at this point, I don't have any other explanation.

Any help with this is appreciated.

Thanks,
Barry - N4BUQ