Toshiba 32av833G PSU schematic (missing parts)

[Dannyx]

Good day folks. I'd like a bit of help with this telly here: it's a Toshiba 32av833G with a pe-3131-02un-lf power supply. Someone had been inside it before me and removed some components from the PSU, presumably in an attempt at fixing it which didn't come to fruition unfortunately (I hate it when people do this)...they were kind enough however to leave some of the parts they pulled out in a little plastic baggy inside the cabinet.
Looking at the failed parts, they belong to the standby circuit and I can tell this unit suffered a voltage spike on the mains: the main cap is blow on this guy and so is the standby IC and a couple of other SMD components on the back. These are the biggest issue. I launched a similar thread asking for help on a local forum and along with doing some research of my own, I was able to identify the IC itself: apparently it's a A6069H, but the remaining parts are a bit of an issue: there's a missing thru-hole zener, a fried SMD resistor and a burnt trace between two SMDs on the back...quite a lot of work. I could not find a schematic yet, so perhaps somewhere can help. I'll post pictures of the board and the affected area tomorrow hopefully, to at least maybe fix it "by ear". I imagine that IC is going to be pricey, so I don't want to go for it until I have the rest of the components. Cheers and thanks for any help.

[momaka]

Re: Toshiba 32av833G PSU schematic (missing parts)

When you post the pictures, I think we will just have to go fix it "by ear".

But it any case, the A6069H IC shouldn't be expensive. The fact that you know what it is is usually a good starting point. Its datasheet should have a sample circuit inside, which in most cases will tell us what parts need to go where and have what value.

I am more concerned about the blown input cap though. - Yes, it could be that it blew because of a voltage spike. But it could also have blown if the set has an APFC circuit - those APFC circuits love to blow the primary cap, along with many other parts like the standby PWM/FET IC. But I guess we will see once we see the pictures - literally!

[Dannyx]

Re: Toshiba 32av833G PSU schematic (missing parts)

Ok guys here's some pictures of this board. I got myself an a6069H after all, which is hopefully the correct one. Here's the datasheet.

The other missing part is ZD604 visible in the picture where IC601 is also gone. On the back though.....this is where things start to get Lionel Messi

There's a burnt trace between JP8 (the larger 0ohm resistor) and D602. D602 appears to be good, so hopefully I can rebuild that trace and we're done there.

R601 has a hole in it. I can just about make out "100" on it, so I reckon it's a 10 ohm resistor going to the VCC pin of IC601, so we're done there too hopefully.

Now ZD604...what could the value of this possibly be ? Looking in the datasheet for the IC, the maximum VCC is 32v, so perhaps this is a 30v zener ? Trouble is if I select a value that's too high, it could fry other components not designed for that voltage. If I select a value that's too LOW, it would fry the series resistor since it's now dissipating too much power (imagine dropping a 40v line down to 30v - only 10v dropped. Now if I use a 5v zener to drop the same 40v line, that's 25v dropped - way more!). What do you guys think ? Should I got with 30 ?

[momaka]

Re: Toshiba 32av833G PSU schematic (missing parts)

The other missing part is ZD604 visible in the picture where IC601 is also gone. On the back though.....this is where things start to get Lionel Messi

There's a burnt trace between JP8 (the larger 0ohm resistor) and D602. D602 appears to be good, so hopefully I can rebuild that trace and we're done there.

R601 has a hole in it. I can just about make out "100" on it, so I reckon it's a 10 ohm resistor going to the VCC pin of IC601, so we're done there too hopefully.

Now ZD604...what could the value of this possibly be ? Looking in the datasheet for the IC, the maximum VCC is 32v, so perhaps this is a 30v zener ?

Yup, you're on the right track there.

I kinda wish you also posted a full view of the solder side so I can make more stuff out, but so far it looks like this PSU has separate standby and main supplies, along with APFC.

Now, the standby/offline PWM controller, APFC controller, and main PS PWM controller all likely get their power from the same primary-side auxiliary winding that is generated by the standby PWM controller.

What I've traced so far is that the primary-side auxiliary winding first goes through SMD resistor R611 (2.2 Ohms), then ferrite bead FB603, then rectified by diode D604, and finally stored into electrolytic cap C610. From there on, power from that auxiliary rail splits for the various primary-side controllers, including the a6069H standby PWM one. So check these components and make sure they are good, if you haven't already.

Trouble is if I select a value that's too high, it could fry other components not designed for that voltage. If I select a value that's too LOW, it would fry the series resistor since it's now dissipating too much power (imagine dropping a 40v line down to 30v - only 10v dropped. Now if I use a 5v zener to drop the same 40v line, that's 25v dropped - way more!). What do you guys think ? Should I got with 30 ?

I think 30V may be getting a bit too close to the maximum 32V rating on that standby PWM controller. Maybe something more in the range of 24-27V will do. But before buying anything, check what the other primary-side controllers' maximum Vcc/running voltage is as well.

I am pretty sure you're not going to see 40V on that primary-side auxiliary winding, so going with a lower voltage Zener is likely not going to be an issue (just don't go below 20V if all of the other controllers have an equally high Vcc voltage rating as your PWM standby IC). If anything, that auxiliary winding probably generates somewhere between 15-25V, and Zener diode Z604 is there only to protect the controllers in case there is a short-circuit on the output of the standby supply, which can make the PWM controller really ramp up its output and thus momentarily make the auxiliary rail voltage higher than normal.

That all aside, since your standby PWM chip blew, I suggest you definitely inspect ALL components associated with the APFC circuit or perhaps even disable the APFC circuit temporarily until you get the standby supply running. Reason I suggest this is because if the APFC circuit overshoots the boost voltage on the primary input cap (C111), you're probably going to end up with a blown standby PWM chip again, if not other parts too. On that note, DO NOT ever test or run this power supply without a primary bulk! If there is one thing that can make APFC circuits damage other components on the primary side, it's an open-circuited or high ESR primary input cap (as the energy stored from the APFC inductor has nowhere to go and can produce extremely high voltage spikes on the primary). This means check the ESR and capacitance of the primary input cap if you are going to reuse the original one. I suspect the power supply didn't blow from a voltage spike but rather a malfunction of the APFC circuit (it's fairly common, actually).

To disable the APFC, removing the APFC MOSFET or APFC MOSFET's Source resistor (if there is one) will do the trick. On your power supply, it looks like the APFC MOSFET may be the one attached to heatsink HS2, though I need a full straight-down view picture of the solder side and top (component) side to verify that.

Last but not least, use a series incandescent light bulb with the PSUs live input in order to limit the current, should something try to go bad. I think I've posted before in other threads of yours how to do that, so you probably know what I am talking about. If not, certainly ask and I will post a link with details.

[R_J]

Re: Toshiba 32av833G PSU schematic (missing parts)

I was looking at a diagram with a str-6069h and off pin 5 (VCC) it has a 10Ω in series with a 1N4749A (24v) zener to ground

[Dannyx]

Re: Toshiba 32av833G PSU schematic (missing parts)

I kinda wish you also posted a full view of the solder side so I can make more stuff out, but so far it looks like this PSU has separate standby and main supplies, along with APFC.

I shall post one today hopefully. Yes, the PSU has a PFC circuit as well.

That all aside, since your standby PWM chip blew, I suggest you definitely inspect ALL components associated with the APFC circuit or perhaps even disable the APFC circuit temporarily until you get the standby supply running.

I reckon that part is fine, or at least I didn't notice and shorts or burnt components, unless the IC is somehow damaged internally.

This means check the ESR and capacitance of the primary input cap if you are going to reuse the original one.

Obviously not reusing it: it's been blown to smithereens so it's going in the trash (the previous guy was kind enough to remove it for me)

Last but not least, use a series incandescent light bulb with the PSUs live input in order to limit the current, should something try to go bad.

I always do the lightbulb test when repairing PSUs, even if I know it's been fixed and there's no way it would blow again. Have done it hundreds of times now

I'll go with 19v for the zener. The PFC IC is a FAN something...I believe it runs fine on 19v. That's another thing I need to mention: the zener could be there for "overshoot" conditions only and it's not actively regulating all the time - only if V AUX rises above XX v....just a thought.

[Dannyx]

Re: Toshiba 32av833G PSU schematic (missing parts)

Another reason I believe the PFC booster is fine is because funnily enough the fuse is fine, so I imagine it would've blown if it were a PFC fault.

EDIT: Here's some more pics: one of the full board and one up close of the problematic area....hope they're clear enough. I can never get the lights to shine properly.....

[momaka]

Re: Toshiba 32av833G PSU schematic (missing parts)

I always do the lightbulb test when repairing PSUs, even if I know it's been fixed and there's no way it would blow again. Have done it hundreds of times now

Ah that's right.
I think I might have been confusing you with another member.

EDIT: Here's some more pics: one of the full board and one up close of the problematic area....hope they're clear enough. I can never get the lights to shine properly.....

Thanks. Should be helpful if you get stuck and we need to help you. But looks like you got this down pretty well. Just replace the burned parts above and hopefully all should be good. Hopefully.

[Dannyx]

Re: Toshiba 32av833G PSU schematic (missing parts)

I rebuilt that burnt trace and replaced the 10ohm resistor and now I'm waiting for my diodes to arrive - I'll go with 19v...hopefully nothing blows. I'm not worried about the IC itself, since we know that can take up to 30v, but I'm not sure the rest of the components feeding off that regulated line would be so tolerant to large voltage jumps...yikes :|

[momaka]

Re: Toshiba 32av833G PSU schematic (missing parts)

Should be fine.
Maybe get several different Zener diodes so that you can experiment, in case the 19V one is too low and doesn't work / burns out.

Also, just a though: did you check the output rectifier(s) on the standby output side? Maybe something was shorted there and that's what caused the standby IC to ramp up its cycle very quickly, making the Zener and that trace burn out?? Again, that's just a thought.

[Dannyx]

Re: Toshiba 32av833G PSU schematic (missing parts)

Also, just a though: did you check the output rectifier(s) on the standby output side? Maybe something was shorted there and that's what caused the standby IC to ramp up its cycle very quickly, making the Zener and that trace burn out?? Again, that's just a thought.

I believe I did and found no shorts. I got myself 19 and 22v diodes but will start with the former...was supposed to get them today, but didn't....

[Dannyx]

Re: Toshiba 32av833G PSU schematic (missing parts)

Sent the guy who runs errands for our shop to pick up some 19, 22 and 30v zeners and he came back with 20 ones instead of 19....and it works, so let's do our fixed TV dance


One thing I noticed though is that even though these are 20v zeners, the voltage at the cathode ("regulated" side was only around 14-15), but that could be because I took the measurement when plugged in through the "control light bulb"....I didn't take a measure after that. Perhaps the rail doesn't actually EXCEED the zener's 20v rating for the zener to go into avalanche and actively regulate - which confirms my first "theory": it would've probably worked without one since it's for protection only to ensure the rail doesn't overshoot (which would still be a stupid thing to do since I imagine upon startup the rail DOES overshoot a bit, lowering the lifespan of the IC and other components)

[momaka]

Re: Toshiba 32av833G PSU schematic (missing parts)

Congrats!

Perhaps the rail doesn't actually EXCEED the zener's 20v rating for the zener to go into avalanche and actively regulate - which confirms my first "theory": it would've probably worked without one since it's for protection only to ensure the rail doesn't overshoot (which would still be a stupid thing to do since I imagine upon startup the rail DOES overshoot a bit, lowering the lifespan of the IC and other components)

Exactly. Most of the time, those Zener diodes are there for protection, not active regulation.

The aux. rail probably doesn't overshoot that much during startup, as most PWM controllers nowadays have soft-start. But during a short-circuit event on the output, the PWM controller can ramp up the duty cycle very quickly before it realizes there is a short-circuit/over-current condition, which can result in the auxiliary winding(s) voltage overshooting quite high.