17PW26-4 zener

[badboydas]

Hi
I have a 17PW26-4 PSU from a Toshiba that had the blinking standby led, I replaced the bulging caps and a couple high ESR caps. When turning it on it promptly went pop. I am 100% sure I did not create any shorts. Now what shorted was a smd Zener D854 (litraly blew the top off the die), but this zener has no part number or rating on the schematic. Any of you guys able to let me know the value?
any help much appreciated

[R_J]

Re: 17PW26-4 zener

If D854 blew like you said it did, there will be a lot more wrong than just that diode, I can't see how it could blow up in the circuit it is in, Q833 base is on one side and a 22k resistor connected to the +24v on the other.
The zener is likely a 18V sod123 (based on a similar 17pw82)

[badboydas]

Re: 17PW26-4 zener

Yes I asumed there would be, but if I don't know the value of the component pointless taking it any further. My electronics skills don't go very far i only have NVQ level 2 and 3 in electronics and computing sytems and level 2 in signal pathways. But like to dabble.

[R_J]

Re: 17PW26-4 zener

You could post some high quality, in focus pictures of both sides of the board, We can then see what we are dealing with and may notice what is wrong.

[badboydas]

Re: 17PW26-4 zener

Hi R_J
On reflection, It was not a short explosion. I recall now that when reinstalling the PSU I knocked it against the mainboard, and with a cursory glance thought nothing of it. The diode has no charing or burn marks. I'll try and get a photo up.

[badboydas]

Re: 17PW26-4 zener

Heres a picture

[nomoresonys]

Re: 17PW26-4 zener

Make sure you didn't put any caps in backwards, recheck your work, what's going on with 473 and 433 looks like a solder bridge there.

[badboydas]

Re: 17PW26-4 zener

Thanks for the reply, that area has not be touched, apart from when I knocked off the top of the zener. All the caps have been double checked.

[nomoresonys]

Re: 17PW26-4 zener

Do you know if anyone else has been inside it?

[badboydas]

Re: 17PW26-4 zener

On opening I would say no, but can't be sure of that.
There is probably a problem with the PFC circuit, but not too worried about that at the moment, more interested with the value of D854

[nomoresonys]

Re: 17PW26-4 zener

Here's something, looks like service manual with schemos there 4th one from left: https://www.google.com/search?q=17PW...w=1280&bih=585

[badboydas]

Re: 17PW26-4 zener

Thanks for the drawing, but D854 shows no value on all the drawings.

[R_J]

Re: 17PW26-4 zener

Hi R_J
On reflection, It was not a short explosion. I recall now that when reinstalling the PSU I knocked it against the mainboard, and with a cursory glance thought nothing of it. The diode has no charing or burn marks. I'll try and get a photo up.

Are you saying that when you knocked the power supply against the main, that knocked the top off the diode? If that is the case the diode die could still be ok and should function, for now, Check it in diode test with your meter.
The zener value I gave you is from a Sharp service manual that lists D854's value. and the circuit is identical
The service manual also lists R965 as 5.6k and R966 as 1k which matches your board and not the schematic.
Note: the Vestel power supply schematics rarely match the actual values on the board.

[badboydas]

Re: 17PW26-4 zener

Hi R_J
Yes so clumsy, and not thinking any more of it, until you sort of jogged my memory with "If D854 blew like you said it did, there will be a lot more wrong than just that diode"

Unfortunatley pretty sure given the readings (in circuit) it's toast 1.59v +Anode to cathode and 2.1v -anode to cathode.

Sorry I totally missed the values you gave, Thanks.

R965 was confusing me at 5.6k instead of 22k and R966 1k instead of 10k you have an eagle eye.

Thanks I will report back soonish.

[badboydas]

Re: 17PW26-4 zener

My hat comes off to you R_J
All voltages present and correct on the main board connector ST_BY grounded with a 1k resistor. so to recap D854 is a 18volt zener
cheers