60pb660v flogging a dead tv-shop visit req

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

My mates has just right now changed Q202 and we are getting 205v (Drain)centre pin and 1.8 volts on the (source) rhs pin.

But still only getting 4 volts on the 18 rail

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

I think its time to give up

[R_J]

Re: 60pb660v flogging a dead tv-shop visit req

Did you change R217? What about R214? R217 is likely less than 2Ω, R214 could be around 10~33Ω

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

just searching through some old boards

[R_J]

Re: 60pb660v flogging a dead tv-shop visit req

So I take it both of the resistors are open?

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

R214 isnt reading anything -struggling to find R217 sorry found 217 a bit discoloured but still reading 2ohm

[R_J]

Re: 60pb660v flogging a dead tv-shop visit req

R214 opened when the fet shorted, and supplied 205volts to the gate, that 205 volts was also supplied into that poor little ic and it shorted internaly blowing the gate drive resistor. when the fet shorted it also supplied 205v across the Source resistor (R217, located on the top side of the board) so this resistor opened, When this resistor opens it then supplies 205v to R209, which is likely a 10~20K resistor but even that 10 volts could destroy the comparator inside the ic.

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

So tomorrow basically replace the ic,R217,R214 and R209? I will change R214 and see if 5n60 shorts may save replacing the ic again

One thing I did forget to mention R217 discoloured yesterday after 200D1 was installed sorry.

We read R217 as a 1 ohm resistor

[R_J]

Re: 60pb660v flogging a dead tv-shop visit req

R209 is likely ok but when R217 goes open and the fet is shorted, one side of R217 has 205 volts on it, on the other side of R217 you measured 10 volts, Look at the pdf for the ic, and you will see pin3 CS normally would have around 1 volt on it. If that input to the ic is bad, the ic will never work properly because it will think there is too much current flowing through the fet and shut the circuit down.

Also there is a trace going under R209, one end connects to R212, where does the other end connect? I suspect it could be pin2 of the ic?

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

I measured 10v on R209, But you are right R217 is open now thanks (I was still assuming it read 2ohm)

Honestly thanks for all your help R_J I will keep you updated my mate hasn't got the resistors so hopefully get them tomorrow

[R_J]

Re: 60pb660v flogging a dead tv-shop visit req

The 18 volts from D203 is just one of the secondaries of that power supply. There are two other supplies from that transformer, The two diodes connected to diode D208 YV and VSC supplies, and the important one is from D205, It supplies ic203, ic204 (reference ic) and supplies the optocoupler that regulates and adjusts the VY & VSC supply.

Also check the voltage on pin6 of the ic (there is an electrolytic cap off the pin) this voltage should be aprox 10 volts

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

R209, R217,R212,Q202 and the ic as you said all blew after I replaced Q202.

I replaced the above and still no picture but thankfull no sizzle and bang this time. I will check what you have written above thanks

[Agent24]

Re: 60pb660v flogging a dead tv-shop visit req

IC201 might be shorted? R_J says D203 should be supplying an 18v rail but you measure 3.8v at IC201 on what seem to be its input and output. That does not seem right in any case.

Or perhaps D203 is shorted and IC201 is not getting DC voltage correctly.

What is IC201 anyway? Is there a schematic for this?

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

D203 reads OK as a diode On one side there was 3.8v on on it but on the transformer leg side of d203 there was 0volts. Ic201 - part number is as7818a. I think this board maybe beyond our repair. On q202 centre pin there is 205v but no voltages on the others. Pin 6 on 200d6 ic204 reads 0voltage

There's 10v on pin 8 of 1c201 but nothing on the others. Centre legs of the transformer read 205v.

When we remove q202 the pads were still reading a diode across them.i will try and source a schematic for ic201. Thanks

[Agent24]

Re: 60pb660v flogging a dead tv-shop visit req

OK that makes sense then, it's an 18v regulator and likely only outputting 3.8v because it's only getting 3.8v.

You are still getting that 3.8v now, with the new Q202 and IC200 etc?

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

OK that makes sense then, it's an 18v regulator and likely only outputting 3.8v because it's only getting 3.8v.

You are still getting that 3.8v now, with the new Q202 and IC200 etc?

Yes only 3.8v with the new q202 and ic201. All the smd resistors r209 etc are fine . R217 was replaced with a slightly smaller sized resistor bands brown black golf gold.

[R_J]

Re: 60pb660v flogging a dead tv-shop visit req

Have you checked the other secondary voltages coming from this supply? It does'nt just supply 18 volts.
If you are getting about 4 volts on D203, what about D205? and there are two other diodes (mounted on the other side) What is the voltage on them?
Only 10 volts on pin8? R213 (4.7k) could also be open, it should have 205v on one side and the ic pin8 (HV) should connect to the other side Likely should have 100~150 volts.
Whats the number on IC203? I suspect it is also a regulator that supplies another part of the Y-sus board
I suspect ic204 is a 431 reference ic.

What color is golf? The value is likely 1Ω

[Agent24]

Re: 60pb660v flogging a dead tv-shop visit req

Indeed, has it been checked for shorts on all the output rails from this supply? If one was shorted, then the others would show a much lower voltage from the brief pulses as IC200 goes into restart loop.

[thuss]

Re: 60pb660v flogging a dead tv-shop visit req

Have you checked the other secondary voltages coming from this supply? It does'nt just supply 18 volts.
If you are getting about 4 volts on D203, what about D205? and there are two other diodes (mounted on the other side) What is the voltage on them?
Only 10 volts on pin8? R213 (4.7k) could also be open, it should have 205v on one side and the ic pin8 (HV) should connect to the other side Likely should have 100~150 volts.
Whats the number on IC203? I suspect it is also a regulator that supplies another part of the Y-sus board
I suspect ic204 is a 431 reference ic.

What color is golf? The value is likely 1Ω

d205 reads 2.1 v both sides. r213 (47k?) reads 205v one side and 9v the other. The diodes on the other side d207 d206 d208 read 2.1 v both sides .d557 read 205v both sides. The first thing I did was check for shorts i.e with the board in place place probe on chassis and one probe on each pin - nothing. I also ran it probe against mosfet etc still nothing. D556 read 203v and 137 v the other.

[budwich]

Re: 60pb660v flogging a dead tv-shop visit req

I hope that you are measuring for shorts using the resistance mode on your meter and NOT the voltage range.