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Re: Tek 422 ac/dc power supply issues

 

glad to hear the DC/DC converter is working that should be a relief.
so why is the Ac-Dc linear causing an issue?? bad rectifier? or one/both of the filter caps bad?

it is 9am here, had a chance to try a pair 2n5881, 2n5039, 2n3055, and Mj10000 earlier this mourning.
11.5VDC input and looked at the waveforms junction D1176/77
I had attached sockets and left them dangle off the side for testing...now where did i put that heatsink??
the MJ10000 (Darlington) would not give stable waveform- kinda expected it may not work.
it does not seem to matter much between the rest. The venerable 2N3055 drew the least current (3.5A) and was stable, 2n5039 a bit more current and stable same with the 2N5881. not having heat sink limited the "on" time. Conclusion- The Chopper xsistor is not too important which were my original thoughts prior to over thinking a replacement. It appears the venerable 2N3055 should be fine. I wonder why the used the 2n1899??...I may find out later when i get the rest of this darned thing working.
I still do not understand why I do not have a leading edge anywhere close to "per the book" . I think the "on" time is too long. I may have to go back prior the choppers....I only have the PDF of the AC/DC supply and the waveforms are really hard to see...they were in blue in the original and obviously did not xfer well.

I also did look at the waveforms with and without scope attached same waveform just 0.5A more current draw.
nice square wave at the Base of choppers.
I will post some pictures later today of the 3055 after I get them off the tablet thing. lots of other stuff that needs be done prior my being gone for the next 10 days (performances/rehearsals/lots of driving- hate the last item)
搁别苍é别

On 2018-04-24 11:46 PM, Jeff Urban wrote:
It just ran off DC for a whole day, literally 24 hours. Stayed cool as a cucumber. The supply was about 16 volts with 1 volt of ripple, mainly sawtooth.

Next I go one of two ways, either inject the DC onto where they put it off the transformer, like at the thermal cutout, without external filtering, or to disconnect the load from the transformer and plug it in and see if it gets hot. I think the voltage was a bit low, but I attributed that to low line voltage. Maybe not. I might have a bad transformer.

I think internally is has 2 X 1,300 uF for filtering, I'll leave the external 10,000 uF out of the circuit and see how much ripple I get. It should be the same and put that question to rest.

On yours I have been thinking, a better mounting arrangement can be had. there are holes for the base and emitter leads, or wires pigtailed off them, and the bolt will take care of the collector. I would put put them on the metal side, which I think is flat and should have more room than the PC board side. I'll look at mine one more time and figure out a good replacement. Now I am thinking maybe the ft is maybe not that critical, with it switching at such a low frequency, 3 MHz might be fine, not sure.

That driver transformer might only show 3 volts DC going to the primary but there is obviously a pulse involved. Since I'm sure mine switches right and I again have the bench space I can get some relevant waveforms. So figure out which ones you want or think you will need and I'll add in the ones I think will help and I'll get them fairly soon. I now have my own camera again so I don't have to borrow one anymore. It is actually not as good a camera as the one I had been borrowing but it seems to have more lens range in the way of going wide and the macro function. It's only 5.1 megapixels but I downsize pictures anyway so they don't take forever to load. It will do.

I think I am going to modify my bench power supply to go up to 3 amps instead of 2, this thing pulls about 2.3 amps, sometimes less. It's a damn shame not to be able to have a nice ripple free supply because of 300 stinkin' mA.
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