Re: Tek 422 ac/dc power supply issues

Renée
 

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 .

what /where is CR 1224?? do you mean D1224?
but if the Ac is not supplied to the diodes.....how can..??....
well I think a typo? I missed something?

I do have a question regarding the "on duration" for the choppers, as the input voltage increases. obviously if the duration increases so does the current and heat.
So if the osc/pulse width go haywire as the input V increases, I am inclined to look at the regulation which is controlled by feedback circuit (-12V) on the DC-DC board.
might want to monitor E of Q1104/14....or look at the C the other side of the diode to Pri T1171 see if instability is being generated further back

I looked at the waveforms you posted earlier and they look good...like the pictures on schematics ( I just found manual with barely readable waveforms)
_YOURS:_

At ~16 volts in;

50 uShttps://groups.io/g/TekScopes/photo/44484/2?p=Name,,,20,1,0,0

perfect!! not like mine which collection is here:

https://groups.io/g/TekScopes/album?id=44362

(Note -all mine are run at 11.5VDC input as if it was battery operated. connection is at junction of D1176 and D1177. I tried to label the picts with some info all AC scope input)

re the instability / Ringing- as the heat rises so does the gain of the xstr ( as I understand). in fact the instability picture looks similar to when I tried to use Darlington for the choppers...too much gain? it is really hard to see whether the transistor is actually turning off long enough for the appropriate duty cycle at the higher voltage.
causing the I increase causing the heat to rise......
_YOUR_ ringing picture where you are unable to get stable view

now at ~30 volts in;

50 uShttps://groups.io/g/TekScopes/photo/44484/4?p=Name,,,20,1,0,0

I am thinking a .001uf across the pri of T1201 to center?.. might help...hmmm maybe the .01 or the D1177/R1177/C1177 combo (same on other half 1187's) for the anti ringing are having issues.....

so where is the ripple originating? the bench supply? I need

I am going to be around but away from the bench....out of town, I will bring my stuff to think/study..etc...

Renée
PS realizing all the info is not sent to the group for easy understanding....thanks to others for the heads-up...learning a lot from the other threads.

On 2018-04-26 11:34 AM, Jeff Urban wrote:
HEY RENEE !

In case you're watching right now, disconnect C 1224 and see what you get. Just clean disconnect it.

I cranked up the input voltage on mine and it made CR 1224 short. Then I got a very subdued waveform at the choppers. I got parts changed and it still wasn't right, and then C 1225 exploded.

More details after the heat run.

I might just have to open up a beer even though it is too early. (after the heat run)


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