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Test equipment repair - Printable Version

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+--- Thread: Test equipment repair (/showthread.php?tid=5640)


Test equipment repair - Eric Adams - 12-24-2012

I am wondering if anyone can help me. I have a signal generator that needs some repair. I was troubleshooting a radio and I think I touched the wrong terminal…OOOPS. The power light is on but it no longer puts out a signal.
It is a B&K Solid State model 2000D. Would you know of anyone in the area who can repair it? I live in Lake in the Hills. NW of Chicago near Crystal Lake. So far the links on my club's web site haven't helped.
I would be happy to drop it off at their location or ship it..
Thanks,
Eric

RE: Test equipment repair - TA Forbes - 12-24-2012

Hello Eric: when you use a sig gen to troubleshoot or align it is always a good idea to have a small, vic .01 mFd on the end of your hot probe to isolate it from any DC present.

Try Roger Kennedy at alltubetesters.com and see if he can help.

RE: Test equipment repair - Eric Adams - 12-24-2012

Thanks TA,

I was using a.1mfd. Not a good move, huh?
I'll try Roger.

Eric

RE: Test equipment repair - morzh - 12-25-2012

Eric

Capacitance itself almost does not matter, not for killing the generator.
What matters is the working voltage. If you used a small WV cap and it was destroyed, then it could've taken out something behind it.

Your gen probably has a potentiometer - attenuator, whose wiper then somehow is connected to the output. The pot could've died if the cap shorted.

Start with 1) turning the gen off and DISCONNECTING it from the mains, 2) take an ohmmmeter and see (if you have the sch) if your pot is OK or not. 3) The pot in its turn may be connected through another cap to a, say, cathode follower. See all elements there - the load resistor, that may go from the cathode to GND, the cap. I somehow think the extent of the damage is not likely to go beyond the output buffer stage.

Mike

RE: Test equipment repair - TA Forbes - 12-25-2012

Agree with Mike. If you were using a .1mFd isolation it should have protected the sig gen, unless the V rating of the cap was too low.

RE: Test equipment repair - Eric Adams - 12-25-2012

Well, the cap is a .1mfd @600volts so I guess it wasn't my fault. I needed to know that because I want to make sure that when it is repaired I can still use a .1mfd cap.

I think I have someone to repair it.

Thanks,
Eric

RE: Test equipment repair - morzh - 12-26-2012

Thinking of it, what could've potentially happen was that a larger than necessary capacitance, when connected to a high voltage, created inrush current through that pot that exceeded what was acceptable. This would not happen if it was connected to a, say, a grid voltage via bias resistors that are high in value, but if you accidentally connected it to a B+ plate supply that would be able to do it. This is where a lower capacitance might've saved the schematic due to a lower inrush.

Anyways, if you point us to a sch of your gen, we'd be able to try to point you in the right direction.

As for the value of that cap, in the future try to use the smallest possible value that still give you acceptable impedance at the lowest RF frequency: this way you both can provide an adequate input for your RF amps and avoid a destructive inrush no matter where you decided to touch your receiver.