XPost: sci.electronics.design
From: pcdhSpamMeSenseless@electrooptical.net
john larkin wrote:
> On Sun, 13 Oct 2024 17:10:30 -0000 (UTC), Cursitor Doom
> wrote:
>
>> Gentlemen,
>>
>> Last week I got an old (1968) pulse generator out of mothballs and managed
>> to get it fully functional again. However, before replacing the case, I
>> (true to form) dropped it on the bench and something on the PCB must have
>> shorted out against the metal tools it fell on, because it no longer works
>> properly.
>> I've found an issue with the principal oscillator. It's generating
>> distorted sine waves. It's a wien bridge type using BJTs as the gain
>> element and fine tungsten filaments as thermistors, so should produce near
>> perfect sine waves before they're chopped and shaped by subsequent
>> circuitry, but since the fall, it's not.
>>
>> Here's the oscillator output:
>> https://disk.yandex.com/i/eKAe95xMsiIvNA
>>
>> I found some weird periodic spikes on the power supply rails in the
>> oscillator stage. They are actually present on the rail, not just picked
>> up by the ground lead of the scope out of the ether, as I used a short
>> ground clip in this instance. I'm not sure if these could cause the
>> distortion or not.
>> https://disk.yandex.com/i/eKAe95xMsiIvNA
>>
>> I'm out of ideas. What could cause such distortion if the PS rail isn't
>> responsible?
>>
>> Your pal,
>>
>> CD.
>>
>
> Maybe the light bulb broke.
>
>
It would have to have failed short-circuit for the gain to be too high, and
that’s not the usual failure mode.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
--- SoupGate-Win32 v1.05
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