Pvm-1953md horizontal output transistor - Videokarma.org TV - Video

freakaftr8 · #1 11-21-2019, 12:19 AM

OK not too sure how many people have or has not worked on a Trinitron PVM before. I picked up two of these the other day and this one was said to power up with no picture however when I powered it up it's instantly blew the horizontal output transistor after I heard high voltage and degauss come up. I looked around the area for any problematic issues and I did not find any so I went ahead and replaced the horizontal output transistor and had fired it backup with my fingers crossed and then managed to blow up an inductor in location L505.

now I'm confused I did have high voltage and degauss come up again before the inductor blew but the horizontal output transistor seems OK still. Does anybody have a schematic on this particular board? I have a feeling it's going to be a doozie.

It appears the inductor is off the 180v that comes out of the flyback that runs the grid control to the G1 screen adjustment on the neckboard. This is closely related to the base junction off the HOT at 125 ohms reading. This is true with both boards so there is a correlation between the HOT shorting and possibly damaging this inductor?

Oddly I have G1 issues with the other monitor as well however I think this one is a bad jungle ic. What comes up with sporadic colors or sometimes extremely high G1 in and goes into AKB shut down. If I freeze the jungle ic then the screen goes dark but when it comes back it looks normal.

freakaftr8 · #2 11-21-2019, 03:59 PM

Alright I'm stumped. Without an actual schematic, what the hell is this thing? The board labels it as an inductor. L505. But it doesn't read like an inductor. it's high resistance until voltage applied.... it has 2 painted dots representing the Uh rating. there are a bunch of these on this board. Its retained in some type of mylar package.

freakaftr8 · #3 11-21-2019, 07:45 PM

Found out. It's a 41 microhenry inductor. Since I have 2 monitors, one with the flamed out inductor and the other one with a low reading at the 180v line, (connected to this inductor) both read open...

As far as I know, an inductor should read near zero correct?

old_tv_nut · #4 11-21-2019, 07:52 PM

correct

freakaftr8 · #5 11-21-2019, 08:24 PM

I wonder what cause in inductor to flame out or go open the 180 V goes directly into this CRT neck board unless the CRT is shorted.

On the second monitor, The weird thing is the board with the open inductor with the 180 V line that goes into the CRT that monitor worked except it would sporadically either be high screen retrace lines or when you turn it on it would be blue or red or green or yellow. But with that one if you crank the brightness and contrast past halfway the screen starts color bleeding I'm wondering if the drivers were getting low voltage

freakaftr8 · #6 11-21-2019, 09:25 PM

Darn. Replaced the bad inductor and it power cycles by itself a few times and blew another horizontal output transistor. Oddly nothing tests shorted off the emitter or collector. I can hear a brief fire up of HV. Maybe bad flyback?

freakaftr8 · #7 11-21-2019, 10:48 PM

Does anyone have any idea what kind of diode and rating this is? Its shorted. The odd thing is the other board has this diode shorted as well and has a low 180v supply coming out of that pin. Also, I found a 47uh inductor to replace that 41uh inductor. and replaced the HOT again...

Electronic M · #8 11-22-2019, 08:59 AM

Possible there is a cap on the neck board that filters the 180V line and has gone leaky.

freakaftr8 · #9 11-22-2019, 09:37 AM

That was my assumption but I changed out all the capacitors on the neckboard just to be safe.. For the diode I'm considering on using a rectifier diode I'm looking at a 200 v 3a considering it runs on the rail of the 180v

zeno · #10 11-22-2019, 01:07 PM

Lift the diode, its gotta have numbers on it. You need a fast
switching diode like the old ECG552. Got to use the right thing.
Sony often used small coils for a fuse / inductor.
Its probably the 200 V supply for the 3 drivers. Usually goes like this:
FBT winding to coil or low ohm resistor ( fuse) to anode of diode.
Catode to cap to GND typ 5 or 10mfd.
That goes to the CRT for the driver collectors. Thats it.
Sometimes the cap dont go tp GND but to the 120V main supply.

The symptoms are like 200V fail. You can get any of the following:
Brite with retrace then HVSD, shading, bleeding, jailbars, bad CRT look.
It a common problem in 99% of color TV's, all brands. It put many
cases of beer in the fridge

73 Zeno

LFOD !

freakaftr8 · #11 11-22-2019, 04:06 PM

But do you suppose this would this also cause the HOT to short? I guess I'm kinda beating my own drum since I found the base off the HOT to be inline with this area of destruction. lol

One monitor works with high G1, the other blows horizontal output transistors but both have the same failed components.

freakaftr8 · #12 11-22-2019, 04:50 PM

Well thru my parts stash I found a BYV26E ultra fast avalanche sinterglass diode and a BYV28-200.

I'm thinking the neckboard cant possibly more than 1 amp. I may be mistaken. but on the voltage 1000v is more than enough to handle considering it's on the 180v line.

freakaftr8 · #13 11-22-2019, 08:49 PM

Ok so I went ahead with the BYV26E. The monitor powers up now to an overdriven G1. Just like the other one is doing.

Now I'll be looking at the neckboard for a 39ohm resistor that maybe went high. Got this info from a friend in the Los Angeles area that specializes in Sony PVMs. Stay tuned..

freakaftr8 · #14 11-23-2019, 12:16 AM

So it turns out the neck board is the problem I swapped it with the other neck board and problem solved. I have G1 control back.

G1 control has no effect on the bad neckboard. it's gone full tilt. Potentiometer is good.

Also the power supply is causing the raster to pulsate. I recapped it and same issue. Something is not smoothing the DC. The other power supply solves this issue.

freakaftr8 · #15 11-23-2019, 03:53 AM

Ok the uncontrollable G1 was a bad 39ohm 1/4 watt resistor on the neckboard.

So to recap, a shorted diode at location D515, an open inductor at L505 and a bad resistor on the neckboard at location R760.

This brought the picture back and 180v at around 190vdc.

Still have a power supply issue on one monitor. A crawl in the picture. Its narrowed down to the power supply board which is a stand alone unit. Replaced some of the caps already with no improvement. I'm suspecting main filter cap. Even though it tests good my meter cannot test for leakage.