Codegen 350XA supply

[tom66]

Re: Codegen 350XA supply

If you touch the isolated scope you will get a live-earth short which will hurt a lot.

[milesy]

Re: Codegen 350XA supply

The flats will vary in width to maintain a constant 12V average on the output filter caps, as the load varies.

If you're going to try measuring the primary, remember to float the DUT with the isolation transformer, NOT the scope.

should have said got the flats detail thanks

why the importance of having the DUT floated instead of the scope?

[milesy]

Re: Codegen 350XA supply

hi escort - why would you think that using 450v caps would be an issue?? i cant see a problem using a higher rated cap?

[Escort Eagle]

Re: Codegen 350XA supply

I have not used 450V capacitors ratings before . I have always used 200V ratings . So, I am not sure Double Capacitors of 450V ratings are safe here or not !! Do it at your own risk !!

[b700029]

Re: Codegen 350XA supply

ok thanks rievax ....well now im scratching my head....for sure on my unit the cathode is definatley double the anode so yes its passing both cycles however i thought that the flat section between each peak looks wrong......

The flats will vary in width to maintain a constant 12V average on the output filter caps, as the load varies.

If you're going to try measuring the primary, remember to float the DUT with the isolation transformer, NOT the scope.

[rievax_60]

Re: Codegen 350XA supply

A faulty 470uf-200v capacitor might explain the messy 12v cathode waveform. There could be a 100Hz amplitude ripple on the waveform that the CRO might not show us while set to a fast timebase.

[milesy]

Re: Codegen 350XA supply

thanks Rievax yep i have an isolation TXFR for that........based on your comments are you suggesting that the caps are bad so excess ripple is coming through the main tfxr and mucking up the regulation?

[rievax_60]

Re: Codegen 350XA supply

Milesy, Just in case you do not know. It is not possible to safely reference your CRO to the live/primary side of the power supply without using an isolation transformer.
One way to test for a faulty 330uf-200v capacitors is to measure the AC ripple with a multimeter. But only if you can safely position the PCB outside of the case.

[milesy]

Re: Codegen 350XA supply

so escort, ill give this a try later i have some 330uf 450v caps sitting around which should be ok to try with........BUT the question i have is why ??? why would those caps cause this fault, can you explain the theory

thanks

[Escort Eagle]

Re: Codegen 350XA supply

OK, milesy . I hope it is 0.06V without Load also . You are always busy for Secondary side and wave form . But this problem is raising not for secondary side . You are searching in wrong Side . This problem is raising for Primary Side .

Just change the Primary main two Filter Capacitors 470mF200V . I know they are looking absolutely fine . But they have still problem . This problem is raising for these Primay Capacitors only, not for secondary Diodes or capacitors . Just Replace those capacitors and your power supply will be 100% OK .

Such ratings capacitors are hardly found in the market . If you found you are lucky . Instead of new capacitors - you can use old capacitors from OLD power supply from the Junk . If OLD capacitor are 330mF 200V, you can use that . Most of the power supply use 330mF 200V ratings capacitors .

Replace those capacitors and you are all done .

Thanks

[milesy]

Re: Codegen 350XA supply

thanks rievax.......i wish i could find a working one of these to compare it to...would make life a little simpler

[rievax_60]

Re: Codegen 350XA supply

It is becoming a puzzle. A few more checks you can do.
You can measure the average voltage of the cathode waveform with a multimeter. The reading should be the same as the other side of the power choke winding, at the 12v output.
Also look at the waveforms with the CRO set to a slower timebase. This might show if the power supply is running in busts rather than continuously as it should be.
Also check the outputs for excessive ripple.

[milesy]

Re: Codegen 350XA supply

ok thanks rievax ....well now im scratching my head....for sure on my unit the cathode is definatley double the anode so yes its passing both cycles however i thought that the flat section between each peak looks wrong......

rechecking my levels seem to be about the same as yours......30v peaks ...my photo may not give the right impression - taken with a digital cam on a slow exposure

so if the signals are the same as shown by rievax - where do i start looking now??

[rievax_60]

Re: Codegen 350XA supply

can anyone confirm for me that the trace shown on the cro above is NOT the correct shape??

Im not certain why your waveform looks unstable. It might be something wrong with your CRO.
I took some waveforms from a 350XA that I found here.
Notice the cathode waveform is double the frequency of the anodes' waveform. This tells me that both diodes are passing the positive half cycles from the transformer.
What is the peak voltage of your waveform? Mine is 30v.

I have a 27Ω load on the 12v rail. The waveforms look very different without this load.

[milesy]

Re: Codegen 350XA supply

yep centreline

[tom66]

Re: Codegen 350XA supply

Where is your ground on the screen, the centerline?

[milesy]

Re: Codegen 350XA supply

can anyone confirm for me that the trace shown on the cro above is NOT the correct shape??

[milesy]

Re: Codegen 350XA supply

hi escort - with the supply loaded the grey wire measures 0.06 vDC - so essentially zero with the yellow wire sitting at 6v

[Escort Eagle]

Re: Codegen 350XA supply

OK . There is another option . Check the Voltage on PG supply . PG is Gray Cable . What voltage present in PG Cable ?? Before measuring PG Voltage, You must turn on the Power supply .

[milesy]

Re: Codegen 350XA supply

hi guys sorry for the late reply back to this.....Escort Eagle i havent been able to connect a monitor to the MB but i would suggest that there is not action from the board anyway.

i got out the cro and checked the trace on the rectifying diodes for the 12v line (two diodes to a bracket from above) and this is what i get


IMGP9565.jpg by Adrian Miles Photography, on Flickr

so it looks to me like im missing half of the trace - from well before the rectifying diodes...i have checked both of the switching transistors at the front end and they appear to be fine........next???