Re: Tek 422 ac/dc power supply issues

Renée I understand .....D1224 and 5 failed before you disconnected C1224....that makes sense...I could not understand how the failure occurred after C1224 was disconnected......never mind.......

yes excessive loading from leaky caps...guess it is time to replace or put the caps through really rigorous testing. i am thinking replacement easier with a known entity.

Yes upon my return I will do as suggested on the C, I will also go back a few spots as I think something is going on there....I may figure the load presented by the BE junction Q1174/84 use a R for load,  then feed/replace the self generating +/- 12V supplies and look real hard at the pulse circuit. I am thinking I have an issue in there since I really do not have a leading edge. the flip/flop...eehh Binary appears to be working as is the steering due to nice square wave presented to the base (and beyond) of the choppers (with the ringing)

Re your  110V supply and V increase failure- I am thinking coincidence for that cap to go bad as no matter what the input V the DC/DC converter should be self regulating. It is a big controlled loop. reading the CAL procedure for the supply suggests such. however I see increased heat generation on the choppers due to the fact the input V is uncontrolled...I  guess hence the heat sinks for the dissipation.

Hope all goes well with the other tasks at hand.....

On 2018-04-26 11:19 PM, Jeff Urban wrote:
"I am not sure I understand. C1224 in on the output side of T1201 and is the feed for the Voltage doubler input cap generating -110V ."

Yes. When I went to a higher voltage it became quite a load. First D 1224 shorted. A leaky C 1224 can cause that. With the diode shorted I got nothing at the negative side, I changed both and then C 1225 popped. I think maybe both caps were leaky. I didn't monitor all the output voltages but it was working and the trace was pretty much where it was before so the voltages didn't climb all that much.

Yes I meant D 1224, for some reason I stuck the CR in there having seen it alot.

Sure, wall AC is not directly applied but that power supply does not directly regulate the secondaries, therefore it does not regulate perfectly. Why else would more input voltage prompt the failure of the -110 volt circuit ?

I don't believe the waveform you are getting at the junction of those diodes is right, and I mean not formed right. The best thing to do is probably to go directly to the collector(s) of the chopper(s). that way you really know the duty cycle. the waveform sat the diodes is not an accurate picture of what is going on at the collector, therefore you can't be sure of the on time. At the collector you get the actual on time, right at the baseline. you can also measure the voltage across the chopper (E-C) while it is on. An overload will cause that to be higher usually. And the duration increases with reduced input voltage or increased load. If your waveforms were actually at the collector the on time would be extremely excessive. But that's not what you're looking at.

My mind is turning to mush. I just got through printing about 50 pages in triplicate of excerpts form a medical record that is about 1,300 pages long, and numbering each page with ID of which file it came from and had to clear a paper jam and all that cool shit. Now I know why they pay office workers. I also worked a bit on some correspondence with a lawyer in Pittsburgh about some mineral rights I don't want to get screwed on. I AM capable of representing myself but don't ever let anyone tell you it's easy.

Tomorrow I got half a day with the cardiologist, I am probably fine but the insurance is paying so since I got a chest pain recently and get the 'funny" feeling sometimes I got referred and have a nuclear stress test. I'll probably be ready for a nap after that, but then I will be probably back on the Tek. I have yet to take the voltage up since fixing the - 110 volt supply. I really thought the transformer was arcing internally. Of course that is probably not all that common because there is not that much voltage there. I need to see if I still get the strange "noisy" part of the waveform. If not, that cures that much but not the heat. If it is gone then good, the thing is better but just not all the way yet.

So when you get back to it, put the scope probe right on the collector(s). Let's see THAT waveform.

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