fdt-5bx5 Vertical Issue

[vol.2]

I have this fdt-5bx5 Sony watchman from the 90s that used to work fine. Many years ago I was doing a setup on it and I screwed something up and the vertical IC went out. I had a bag of what should be NTE equivalents on hand and I tried to use one of them and for whatever reason it didn't work.

This was very long ago and I can't remember exactly what happened, and I'm trying to clean it up now.

So I went in and found that I do have some vertical, it's just very weak and the whole top portion is stretched out, like the way it looks when a vertical IC is going bad or about to blow.

I measured the supply and I found that the 22V supply is on around 14.8V, which is clearly wrong, and no wonder the Vertical isn't verticalling.

So then I looked at the PSU board, but I don't see anything weird. I see the 24V is down at 14.8 like it is on the Vert IC, so that's at least consistent.

Tested a few caps but they look good and everything is very clean and minty and they used Rubycons and this is a ~1994 TV made in Japan with no SMD lytics so I think it's all good.

Could be the NTE replacements don't work? Would they bring down the 24V?

I attached the datasheets of the two Vert ICs. I don't have the service manual in PDF. I have the Sams somewhere, but I also have a link to a forum that someone posted the whole thing here: https://shmups.system11.org/viewtopi...ad7b6#p1497626


Any ideas on where to look?

LA7830.PDF

nte1773.pdf

[Alex KL-1]

The IC is too hot (= high current drain)?
Or, the 24V have some series resistor partially open?
EDIT: IC with high current drain can be or a faulty IC or a short in the V yoke.

[vol.2]

Originally Posted by Alex KL-1

The IC is too hot (= high current drain)?
Or, the 24V have some series resistor partially open?

Could be. Not sure how to track that down other than pulling components. I wonder if there's some way I can isolate the power supply and just test that to see if I get the 24V out of it or not. That way I can know if something is sinking current on the main PCB or not.

I need some way to narrow things down.

EDIT: IC with high current drain can be or a faulty IC or a short in the V yoke.

I measured the yoke, and it checks out. The two parts say 0.5ohms and 20ohms on the schematic, and I get 1ohm and 20ohms, so looks okay thankfully.



EDIT:

Okay, I think I found it. Q602, the Mosfet creating the 24V source and it's blown open. Mystery probably solved. I check all the electrolytics in the ~20V sources area and they are all good, and the other little transistor tests normal.

[Alex KL-1]

Great!

[vol.2]

Originally Posted by Alex KL-1

Great!

Thank you!

Yeah, I should get the mosfet in the mail tomorrow, so I can figure out if it works or not pretty soon.