Codegen 350XA supply

[milesy]

Re: Codegen 350XA supply

Ok so if the assumption is correct i should be able to hook the Cro up to the anode of the regulating diodes and see a trace basically the same but alternate polarity on each anode??

[rievax_60]

Re: Codegen 350XA supply

Ok so if the assumption is correct i should be able to hook the Cro up to the anode of the regulating diodes and see a trace basically the same but alternate polarity on each anode??

With the power supply lightly loaded, on the diode anodes there should be a stepped square wave. It alternately pulses negative and positive with zero volt dead times in between.
It should look exactly the same on each anode, but 180 degrees out of phase.
If both diodes are working, there should be a square wave of double the frequency at the common cathodes(middle pin). The bottom of this square wave should not go more than about a volt negative.

[Escort Eagle]

Re: Codegen 350XA supply

OK. It generally happens when the Output caps are gone Bad or when Caps Pins soldering with PCB gone bad . I hope you have no output Badcaps and Bad soldering because you have tried those method already .

Now you connect the Power supply with Motherboad and tell me is there any Display in Monitor ?? If I am not wrong, then the power supply has no display . Please ensure me this power supply has display or not .

Thanks

[b700029]

Re: Codegen 350XA supply

Escort Eagle, he's not going to get anything to work with the 12V rail at half its nominal voltage.

Diodes on a bracket!!

Replace the two diode-bracket with a proper rectifier. one of them could be toast

You mean diode on a bracket

...The possibly only advantage of building it this way is so you only need to replace one diode instead of a 2-diode pack...

[c_hegge]

Re: Codegen 350XA supply

^
The single diode is for the 5vsb. I was referring to the 12V rail before. Admittedly, putting the 5vsb diode on the heatsink is a much more sensible option than Bestec and Delta putting it next to the 5vsb input cap. Who would have thought that Codegen could do better than Bestec and Delta?

[kaboom]

Re: Codegen 350XA supply

While you're at it, replace the small ceramics in the RC snubbers on the secondary side.

Had one of these junkers where on of the 10 ohm resistors in a snubber was totally incinerated.

It was under some unburned dust, so I think the ceramic cap shorted shortly after the supply was first used, with the dust building up over the (short?) life of the system.

[Escort Eagle]

Re: Codegen 350XA supply

Escort Eagle, he's not going to get anything to work with the 12V rail at half its nominal voltage.

12V is dropping to 6V at loaded condition . At normal state it is showing 11V . Now First I need to know - Is the Display is showing or not . This Display's presence or absence will separate the problem of voltage dropping . This Display's presence or absence will tell you - why the voltage is dropping - Is it for Primary side or Secondary side . Display's presence or absence will identify that . This is why - I need to know Display's presence or absence First .

Thanks

[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???

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

[milesy]

Re: Codegen 350XA supply

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

[tom66]

Re: Codegen 350XA supply

Where is your ground on the screen, the centerline?

[milesy]

Re: Codegen 350XA supply

yep centreline

[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

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

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

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

[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

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

[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.