25K7401 - Test Point Info

[wrkey]

Working on referenced monitor.  It has the P763 chassis board.   Vertical collapse.  Cap Kit done.  TDA1771 is known good.  Tested lost of the V.D. section resistors and found nothing out of spec.  I have the 2 page schematics for it.

What I don't have is the Test Point voltage specifications.  I do see some information on the schematics but many of the TPs are not on there.  The one on the board that does have a voltage reference printed on the PCB is TP204 which is supposed to be 15v, but I am getting 13.2.   At VV1 (yellow jumper) I have 24v +/-0.1   But I would like to know the other voltages before I go jacking with it too much.  So....

Can anyone reply with the test points on this board and what the values should be?
If I adjust the B+ could this bring up the voltage on TP204?  I am concerned about ramping up the B+ because A)I don't know what the other test point voltages look like and B)they glued that pot down good and I will have the pull the pot to try and get all the glue off.

Any suggestions will be appreciated.

Rusty

[princess prin prin]

For the vertical deflection you want to check 12V on pin 20 of U701 (better use the resistor nearby so you don't accidentally short pins). That comes from the 15V line through a voltage regulator based on Z601. So if you have 12V there you don't have to worry about the 15V source.

Also, check for 25V (or close) on the cathode of D603 (which is coupled to pin 2 of U601). if you have voltage there you know it's also on the anode (pin 9 of U601). You already checked that at TP205 but you need to make sure it's actually going to U601.

If voltages are OK, it gets more complicated as you need an oscilloscope to check U701 is sending out the vertical pulse to U601 (pin 3) or U701 may be bad. Double check C603 in line with the signal (you recapped it but you never know).

You said U601 is good (pulled from good chassis?) but I've heard about fake ones.

[lilshawn]

98% of the time when you have vertical collapse it's the vertical deflection IC. the other 2% of the time it's the power feeding the IC because they usually feed the power through a couple resistors to dump it down and they've gone out of spec. (usually cause the chip is failing causing increased power draw and subsequently increasing the resistance of the resistors.)

i know you say it's known good TDA chip, but the ICs like this are prone to being faked due to it not being produced for quite a number of years now.

at this point, it's getting to be that most CRT specific parts are best pulled from other chassis so you don't end up with fake parts.

also...don't mess with the B+ or xray pots.... its sealed for a reason.

[wrkey]

From above:  "For the vertical deflection you want to check 12V on pin 20 of U701 (better use the resistor nearby so you don't accidentally short pins). That comes from the 15V line through a voltage regulator based on Z601. So if you have 12V there you don't have to worry about the 15V source.

Also, check for 25V (or close) on the cathode of D603 (which is coupled to pin 2 of U601). if you have voltage there you know it's also on the anode (pin 9 of U601). You already checked that at TP205 but you need to make sure it's actually going to U601."

On the R622 that feeds U701 I am getting about 11v, sometimes 10.8.  On D603 I am getting 22v.

So these are low.   Are they low enough for concern or look elsewhere?

Thanks for everyone's help!

[princess prin prin]

They're within range.

Vertical deflection coil on the yoke isn't open is it? Remote board plugged in correctly? If there are no bad solder joints in the circuit and you're confident about your recapping job, reconsider a bad TDA1771.