Sony Trinitron KV32FV27 Power Supply Problem

[cmonkey]

I'm just creating this thread to document this issue so I don't forget what I've tested so far.

Technical Manual.

I've measure CN641 on the power supply board ( board G ) and all the voltages are about half of what they should be. So the 9V pins are measuring about 5V, the 135V pins are measuring about 70V.

I replaced the two large main caps ( C606 and C607 ) and also C643 and C641 with new capacitors without doing any more troubleshooting and strangely the TV worked for about 30 minutes and then started behaving the same way.

I can't figure out if it's an AC or a DC side issue ( I don't know how to test the transformers and don't know their output values), so I just started measuring the voltage points in the schematic that have values. I started with IC601 since that is on the AC side and I can get 120V all the way up to it but then it gets weird. Maybe my multimeter can't measure the voltages coming off it?

I also tested the transistor's diodes (still in circuit) and got some strange results. On the bottom of the board the pins are labeled B1, C1, E1 and B2, C2 and E2 so these must be each diodes base, collector and emitter.

I get voltage drops as follows -

B1 -> C1 = 0.459
B1 -> E1 = 0..529

B2 -> C2 = 0.459
B2 -> E2 = 0.529

Those are as expected, but then I measure across the two diodes and also got a voltage drop.

B2 -> C1 = .0529

I'm not sure if this is normal or not. I also get continuity between E2 and C1 so there is a low enough resistance between them to register as a short.

C1, E2 and B2 are also the pins I get weird voltage readings on as well. Maybe I need to test it out of circuit?

Here is a photo of the schematic.

[cmonkey]

Preface for today - this TV is acting very strangely, whatever fault it has on the power supply isn't constant. About 1 in 10 times I turn this thing on, it's got good voltage coming off the power board and everything works for a few minutes. Then the voltage starts slowly dropping and the picture starts warping until I turn it off. Then it's back at about half the right voltage.

I'm just creating this thread to document this issue so I don't forget what I've tested so far.

Technical Manual.

I've measure CN641 on the power supply board ( board G ) and all the voltages are about half of what they should be. So the 9V pins are measuring about 5V, the 135V pins are measuring about 70V.

So this isn't entirely accurate. The 5V standby voltage is good (pin 10 on CN641) and the power on voltage (pin 11) is also good at about 3.6V.

I also think the short between E2 and C1 might be ok because they are connected via FB604 which is a ferrite bead and all the other FB components are also measuring the same. I would need to remove IC601 from circuit to properly test it I think.

I've also tested the 3 bridge rectifiers in circuit with just a diode test and they are all measuring good. (D602, D641 and D643)


So for now I have ordered a proper good LCR meter so I can test all the capacitors. My DMM isn't working on capacitance anymore.


Until then I need to figure out how to properly test voltages on the HOT side of this board. I realized I wasn't measuring the pins coming off IC601 properly because I thought it was AC current but it looks like these are DC because they are after the bridge rectifier. Am I wrong here?

What do I use for a ground when testing DC on the hot side of a power supply? Specifically I'm trying to test the pins on IC601 to see if the voltages are the same as in the schematic.

[Donny2derby]

Diodes don't have bases, collectors and emitters. They have Annodes and Cathodes. Transistors have Base, collector and emitter terminals.

If you want some proper help it's best you post up some pictures of all the boards.

[Diah]

in General over all HOT area on PSU the - GND will be references to the main filter CAP -, Cold area will be TV chassis

[cmonkey]

Diodes don't have bases, collectors and emitters. They have Annodes and Cathodes. Transistors have Base, collector and emitter terminals.

If you want some proper help it's best you post up some pictures of all the boards.

So the transistor is tested in diode mode, but doesn't have internal diodes? I'll try to post a photo later.

[Donny2derby]

So the transistor is tested in diode mode, but doesn't have internal diodes? I'll try to post a photo later.

A transistor acts as a switch, a diode is there to allow current to only pass in one direction.

A transistor is 3 terminal, diode has 2.

There is a diode in a transistor so that's why they can be tested in Diode mode using a multimeter.

[cmonkey]

A transistor acts as a switch, a diode is there to allow current to only pass in one direction.

A transistor is 3 terminal, diode has 2.

There is a diode in a transistor so that's why they can be tested in Diode mode using a multimeter.

Ok that's kinda what I thought.

Here's a photo. The AC input is on the upper left. The transistor I'm looking to test voltages on is bottom right. The main bridge rectifier is middle leftish.

Am I wrong is noticing that it looks like the AC is the striped section and DC is non-striped?

[Donny2derby]

I'm not experienced enough to be able to distinguish if it's only AC on the striped and DC non striped but you will only have AC before the bridge rectifier and DC after that.

[cmonkey]

I got around to re-capping the entire power supply board and am still having the same issue. When cold the TV turns on and runs flawlessly for about 15 minutes and then the voltages all start dropping coming off the power supply board.

I just replaced all the electrolytic caps. Not sure where to go from here so I'm just going to start testing various components.

It seems whatever has failed has not completely gone, it's just on it's way out.

[cmonkey]

Forgot to mention, one of the electrolytics did test out of range. C660 tested at 2200 nF but it should have been within 20% of 3300 nF. Regardless that didn't fix the issue.

Gonna test all the non-electrolytic caps next. I'm not sure what other component could work fine for 15 minutes and then fail, other than a capacitor.

[Diah]

II replaced the two large main caps ( C606 and C607 ) and also C643 and C641 with new capacitors without doing any more troubleshooting and strangely the TV worked for about 30 minutes and then started behaving the same way.

I'm not sure what other component could work fine for 15 minutes and then fail, other than a capacitor.

you have cutting / broken at print chart on boards or lost connection one legs of component at the part self.

[cmonkey]

you have cutting / broken at print chart on boards

Sorry, what do you mean 'print chart'?

[Diah]

on boards down side soldering green lines between parts

[cmonkey]

Ok, yea I've looked around for broken traces and cold joints and haven't found anything.

Instead of testing the other caps, I've been getting voltage readings instead and I think I'm narrowing it down a bit, specifically it's a problem on the hot side.

All of the voltages on the pins IC601 are wrong. In fact I'm getting 170V and -170V coming off of the bridge rectifier ( D602 ) and that voltage is making it's way all the way to IC601. I don't have any reference values in the specs or when it was working right, but the voltages on the big caps are also 170V and -170V.

These are what the pins on IC601 should read -

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

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

Here is what they are actually reading -

B1 - -170V
C1 - 21V
E1 - -170V

B2 - 17V
C2 - 170V
E2 - 21V


Also, the voltages on C1, B2 and E2 are all very erratic, jumping up and down by about 1V.



One other interesting thing, the entire AC white line heading back to the AC plug from the bridge rectifier (D602 - pin 3) is .01V AC. Shouldn't this be 120V like the black line?

[R_J]

You need to know the difference between the HOT (primary side) of the power supply, and the COLD (chassis) side. They are marked on the board and the two sides are separated by a white line. When checking voltages on the HOT side you MUST use the negative pin of the bridge rectifier for your meter negative probe. You can not use chassis ground when checking primary voltages.

[cmonkey]

You need to know the difference between the HOT (primary side) of the power supply, and the COLD (chassis) side. They are marked on the board and the two sides are separated by a white line. When checking voltages on the HOT side you MUST use the negative pin of the bridge rectifier for your meter negative probe. You can not use chassis ground when checking primary voltages.

Yes I'm very careful with the hot and cold side, it's clearly marked. Could I also use the negative pin on the AC connector coming in from the electrical cord? This is what I've been doing.

Also, the negative pin of the bridge rectifier is not showing any voltage and this doesn't seem right to me. Maybe I'm not understanding but I thought voltage should be 120 from that pin going back to the AC in.

[Diah]

this is wrong... use the - pins of large main caps of hot area as reference measurements at hot area only.

SMPS will go high only if there power ON signal >3.v syncs to hot area via optocoupler .. if this optocoupler cut off the tv will never turn on.

[cmonkey]

SMPS will go high only if there power ON signal >3.v syncs to hot area via optocoupler .. if this optocoupler cut off the tv will never turn on.

The power-on pin is 3.62V and the standby pins is 4.98V, so these two are good.

[Diah]

The power-on pin is 3.62V and the standby pins is 4.98V, so these two are good.

test the optocoupler of Power on between cold and hot out side the circuit

[Diah]

i think yours hot circuit are fine.... you need to follow and trouble shooting the cold circuit from power on pins till the optocoupler rail... could be changed value from low to high or open