XBOSOZ psu query/problem

dhole

Member
2004-07-26 11:49 pm
Brighton
Hello people

Now i knew there would be problems.....

So i have my boards from Kari (thanks !) I have stuffed all the boards. Thought i would power up the psu without the main board to check it out. i hook up my 50va 55v toroidal and my 50va 12v. turn it o and..... well the 55v torid starts to get hot... and hotter and .... I turn it off. so i checked the AC from it, and its 63.7 ! well I guess our mains is a bit hot as the toroids should be good. I also check the 12v and that is 13.8.

Well I checked all the components rectifying diodes ok (right wayround etc) I thought i would check the output. The 12v side should end up as around 9v and it does but the other side should be 80v and it ends up as 7.3 ! now that aint right... i have rechecked all the components. Can anyone advise where i might look to ? I have two of these boards setup and both exhibit the same behaviour......

dave
 
kilowattski said:
What are you going to be using the 55 volt toroid for? 22 volt rails give you 100 watts. Even your 12 volt toroid may not be sufficient at 50 VA. If you look at the AXE-1.2 spreadsheet at 12 volts a 288 VA toroid is recommended for a single channel. Do the toroids seem to work when not connected to the rectifiers and caps? Show us a schematic and component values so we can help you.

Kilowattski- you are talking about an Aleph X right? dhole is speaking of problems with an X-BOSOZ which uses, I think +60VDC (not plus 80V like in regular BOSOZ....but not sure on this as we still have no schematics for the Kari design:bawling: ) 55VA is plenty for both channels and should not get hot.

What is happening I think is that something is connected wrong and is drawing a lot of current from the one transformer, heating it up.
 
Electrolytic caps the right way around? turn the board over and check that the voltage is right. It is possible that the silkscreen has an error.

What voltages do you get at each pin of the IRF610? It is a 610 on the positive rail, right? You should get 80V+ at the input (drain) and around 60 at the output (source) If the gate is more than 20V higher than the source, the FET is toast. Ckeck the voltage across each zener in the reference string.

the circuit is the same as in the article at passdiy, except that the negative rail has fewer zeners in it and a lower voltage
 
Silkscreen Error?

Someone back me up on this (it's been a long day), but looking at the PSU board shown in this thread http://www.diyaudio.com/forums/showthread.php?postid=698833#post698833 it looks like the silkscreen for the positive regulator's rectifiers is backwards - its negative output is connected to the positve rail as drawn.

Not a show stopper, just put the diodes in opposite the way shown, and all should be fine.

dhole - you should probably replace the positive caps, as they may have been damaged by the reverse voltage. I'm slow enough mine would have popped, you got lucky.
 

dhole

Member
2004-07-26 11:49 pm
Brighton
Thanks alot guys! I think you are right too. I have double checked everything. The components are correct, and I have a a blown capacitor on the +80v channel. I just need to get some more caps , lucky I think I can get them cheap.
I will keep people informed.
regards
dave
 

dhole

Member
2004-07-26 11:49 pm
Brighton
#Kari

I was just going to mail you but you have spotted the thread. Could you mail me off list about possably getting some more psu boards. Just that mine are getting a bit ragged as I have done alot of desoldering to try and find the source of the problem.... :(
dave
 

dhole

Member
2004-07-26 11:49 pm
Brighton
Thanks Guys for the advice. I was thinking diodes.... I have resoldered one board and things are better.One cap on the other board has a bulge in the top so I guess its dead, but the board I have just done seems fine with the original caps. I was quite quick at seeing the fault .
I am getting higher voltages on output though.... +64v and -13v but I guess under load that will lower. Shouldnt fry anything with that should I ?

Dave
 
dhole said:
Thanks Guys for the advice. I was thinking diodes.... I have resoldered one board and things are better.One cap on the other board has a bulge in the top so I guess its dead, but the board I have just done seems fine with the original caps. I was quite quick at seeing the fault .
I am getting higher voltages on output though.... +64v and -13v but I guess under load that will lower. Shouldnt fry anything with that should I ?

Dave

As you said, the voltage is going to drop under load. I think you are fine with those voltages and as i recall it metalman said that we should keep the - side above 10V, so your -13V is fine. I'm going to use 2 9.1V zeners at the negative side so i'm ending up with -14 to -15V.

Anyone else have any toughts?

/Kari