Sony Trinitron KV32FV27 Power Supply Problem

[cmonkey]

I don't see anything that resembles an optocoupler on this board. I followed the power on pin 11 from CN641 back and it goes through a bunch of resistors and transistors. I also looked on the A board and that pin goes directly to an IC.

[R_J]

What happens when the tv shuts down? does the screen shrink etc. or does it just turn off? when it shuts down does the led flash and if it does how many times.
Check or re solder connections on the high voltage transformer (T502) and drive transformer (T501) as well as vert output ic (IC561)
This power supply does not use an optocoupler for feedback.
These sony tv's were quite reliable and did not have many issues with bad caps etc.

[cmonkey]

So if I leave the TV sitting for several days/weeks, it will turn on and run perfectly for 10 minutes. The screen begins to warp around and starts shrinking and color goes away. The sound gets crackly. It then goes to black screen and no sound. This whole process takes up to a minute sometimes but I usually turn it off right away. It's very gradual, not sudden.

After that (and right now) if I turn it back on, I hear a couple of clicks on the power supply and nothing happens except all of the voltages are too low on the power supply board. Degaussing coil also doesn't go.

I'm currently hung up on why IC601 has all of the wrong voltages on it's pins. How does the voltage get bumped up from 170V coming off of the main bridge rectifier to 298V on C2 of IC601? Or should the bridge rectifier be outputting 298V and it's not?

[Diah]

ohh its CRT..of course no Opto.. can you shoot photo on the whole top ?

[cmonkey]

Here is the top, and two shots of the bottom. If there is something specific to zoom in on, let me know. Disregard my dirty solder joints, haven't cleaned them yet. They are not burned spots.

[Diah]

The screen begins to warp around and starts shrinking and color goes away. The sound gets crackly. It then goes to black screen and no sound.

i don't thing the issue at the power boards.... it could be horizontal section... so the high voltage reduced then cut off

switch it ON with out CRT screen boards, check if the sound remain on

[cmonkey]

The power supply doesn't switch on at all when I have it disconnected from the main board, which is expected because the main board isn't getting a power on signal.

Interestingly the TV turned on for about 5 minutes this afternoon and I was able to take some measurements around that IC601 transistor. Even with it on and working, none of the voltages are correct according to my measurements, which is strange.
Also the DC + and - is around 10 volts lower, sitting at 157V and -157V.

My readings -

B1 - -157V
C1 - 1.8V
E1 - -157V

B2 - 1.8V
C2 - 157V
E2 - 1.8V

Schematic says they should be -

B1 - -1.1V
C1 - 153V
E1 - ?

B2 - 151V
C2 - 298V
E2 - 152V

I don't know what to make of the weird readings.

Also, the AC line going from the bridge rectifier back to the white AC in plug was at about 1.4V AC so it might be ok that's it's low.

I've tested nearly all the caps and resistors around IC601 and everything is good. The main bridge rectifier also tests fine.

[cmonkey]

I've tested every cap, resistor and varistor around the AC in and everything checks out good.

I've also not found any shorts anywhere on the hot side.

[R_J]

Where is your meter ground lead connected when you are checking those voltages?

[petehall347]

base emitter voltages generally dont match unless there is a short .

[cmonkey]

Where is your meter ground lead connected when you are checking those voltages?

I've used both the AC neutral pin on the main bridge rectifier and also just the AC neutral pin on the main plug and get the same reading.

base emitter voltages generally dont match unless there is a short .

You mean the B1 and E1 and B2 and E2 pins on IC601?

[petehall347]

I've used both the AC neutral pin on the main bridge rectifier and also just the AC neutral pin on the main plug and get the same reading.



You mean the B1 and E1 and B2 and E2 pins on IC601?

yes . they should be a volt difference . you could try directly base to emitter rather than 2 readings .

[R_J]

This power supply is working... so far. The only problems I have seen in these power supplies is when ic601 shorts and blows R607. If you don't use the bridge rectifier negative for your meter negative you will NOT get the proper readings in that circuit . You should be checking the +B voltage (using CHASSIS ground) and see if it starts to drop when the screen starts to shrink . A common problem on these chassis was one of the damper diodes (D502, D503, D504) going bad

[cmonkey]

If you don't use the bridge rectifier negative for your meter negative you will NOT get the proper readings in that circuit . You should be checking the +B voltage (using CHASSIS ground) and see if it starts to drop when the screen starts to shrink . A common problem on these chassis was one of the damper diodes (D502, D503, D504) going bad

I'm using the chassis on the cold side for the B+ voltage and it does indeed drop when the screen starts to shrink. It drops from 135V to about 65-70V and stays there.

R607 tested fine for me when I tested it.

So I should be using bridge rectifier negative on the DC Hot side?

I'll look at those diodes sometime today and let you know.

[R_J]

I'm using the chassis on the cold side for the B+ voltage and it does indeed drop when the screen starts to shrink. It drops from 135V to about 65-70V and stays there.

R607 tested fine for me when I tested it.

So I should be using bridge rectifier negative on the DC Hot side?

I'll look at those diodes sometime today and let you know.

I know R607 is ok, it is a fuse resistor that goes open when one of the fets in ic601 shorts. obviously, this is not the problem. Once the voltage drops, unplug the tv and check if the horz. output (Q502) or if D502~D504 are getting hot. If it takes about 15 min. to start to shrink, try using a heat gun/hair blower to heat the power supply and see if that speeds up the shrinking, If this does not affect it, try heating around the horz. output circuit. or you could get a can of freeze spray and try colling components on the power supply, It is unlikely to be a component on the primary side of the power supply.

[cmonkey]

The TV is currently not turning on and all 3 diodes, 502, 503 and 504 tested fine.

I tested IC601 again with my ground on the DC negative pin of D602 and got the following -

B1 - -250mV
C1 - 188v
E1 - 0v

B2 - 185V
C2 - 330V
E2 - 188V

So these seem a bit more normal, just 30V higher than spec.

[cmonkey]

I know R607 is ok, it is a fuse resistor that goes open when one of the fets in ic601 shorts. obviously, this is not the problem. Once the voltage drops, unplug the tv and check if the horz. output (Q502) or if D502~D504 are getting hot. If it takes about 15 min. to start to shrink, try using a heat gun/hair blower to heat the power supply and see if that speeds up the shrinking, If this does not affect it, try heating around the horz. output circuit. or you could get a can of freeze spray and try colling components on the power supply, It is unlikely to be a component on the primary side of the power supply.

I've been just generally reading about low voltage problems in CRTs and one thing I came across was a potentially bad/going bad main capacitor in the flyback. Is that true and would you know how I could test it?

[cmonkey]

So I've picked this up again, however, now the TV has does absolutely nothing when I turn it on. Not even any clicks.

I started testing the HOT side voltages, and there is no power going to the bridge rectifier. I made it back to one of the relays and found that RY600 has the 5v on the cold side, but it's not tripping on the hot side, only one of the legs of the relay has 120V.

Problem is, I can't even find this relay anywhere if I wanted to try replacing it.

Does anyone have any tricks for finding old parts, or finding a new replacement?

The part number is 1-755-266-11.

[R_J]

The relay is not your problem, What voltage do you have on the PWRON pin of CN641?

[cmonkey]

I just don't know what to make of this. I let it sit for an hour and now it's behaving like before I left it sit for a few months.

The relay clicks again and I have bad voltages all over the secondary side.

These two are correct -

PWRON - 3.6v
Standby - 4.97v

These are all wrong -

12v rail - 3.8v
9v rail - 1.06v
B+ rail - 57V (should be 135V)