Re: Transformer for HP zr24w



solder wack + my venerable weller WS50 iron.

Found the replacement on a junk PCB (from an old Dell PowerEdge PSU).

Not sure about the max voltage (datasheet says 50V) but I 'm guessing a SMD ceramic cap with the same size and value should be in the same max voltage range....

Re: Transformer for HP zr24w

BTW I wrote a small blog entry on my repair of this PSU

[url]https://whatever.sdfa3.org/hp-zr24w-psu-repair.html[/url]

(as well as an epic rapair of my Tek2445's PSU a while ago, might interest some guys aroud here

[url]https://whatever.sdfa3.org/tektronics-2445-scope-psu-repair-part-1.html[/url]

)Re: Transformer for HP zr24w<br /> .../> (as well as

Re: Transformer for HP zr24w



Before failur, EN/UV is sitting at a normal value (depending on the load, don't remember the steady value), but I measured a rise of the voltage when it became to fail (as to be expected, in fact), so it look like the TNY starts to fail switching enough current in the primary winding (making the output 5V to drop).

As I said, I could not properly probe the switching signals, so I cannot tell which comes first....

Re: Transformer for HP zr24w



yes



not sure. The fact that it would not restart as long as the DFC is running (rising the DC input voltage to 400V) make me think there is general problem with the error detection circuitry in the TNY279.

I have not been able to measure with confidence the probable "root cause" of the failure (I don't have an isolation transformer for now, so my probing capablities are limited).



A TNY279 only cost a dollar or 2, so just replace it and you'll see...

Re: Transformer for HP zr24w

I've received the replacement TNY279 IC and the PSU is back alive!

I've also changed the BP/M capacitor (mainly because I accidently broke it).

I've also desoldered and checked most of the electrolytic capacitors, including the one you mention (filter of the aux rail power) which were all fine (according to my cheap tester, correct value and low ESR).

David

Re: Transformer for HP zr24w

I've digged a bit more.

The bias winding of the TNY279 transformer is used, as describes in the datasheet, to power the TNY279 and allow a very low no-load consumption, but it also powers the CM6807.

So when the TNY279 fails (for some reason I still don't undersand), it cuts the power of the CM6807.

So in order to check the CM6807 part alone, I've tried to run the CM6807 from a bench power supply, and it works fine even when the TNY279 has entered it's failure state.

So now the question is why...

Re: Transformer for HP zr24w

Hi, I'm also trying to fix this PSU. My problem is that the PSU stops itself after a couple of minutes (when cold).

I've investigated a bit the PCB trying to understand the schematic, and there are 2 parts in this PSU:

- one converter built around the TNY279PN to generate the 5V (should be always on)
- one converter built around the CM6807 to generate the 2 other voltages (12v and 19v) and is activated when the 'powersave' pin is put hi (and there a minimum of current sunk on the 5v rail; it won't start if nothing...