Modern TV Repair, anyone? - Videokarma.org TV - Video

YamahaFreak · #1 11-12-2007, 05:06 PM

I pulled a 1993 32" Sony Trinitron set off the curb because I was curious. It has no power at all, not even the little red standby LED. No sounds from inside. One other thing I might ad is that there was a s**tload of dust inside. There are no obvious broken things inside, and the power fuse wasn't blown, so I though it was the flyback transformer, but if that were the case, wouldn't the standby LED be lit? This is a really nice set for the time period, with five-watt stereo speakers, four inputs, variable/fixed audio output, and S-Video capability, among other things. I'd like to get it working if I can.

Picture:

http://img136.imageshack.us/img136/4042/1020775kd9.jpg

radiotvnut · #2 11-12-2007, 05:27 PM

Check the horizontal outupt transistor. That's the large transistor on a heatsink close to the flyback. If it's shorted; the power supply will be damaged. There are two transistors in the power supply mounted on small heatsinks. If these are shorted; there will be a small white fusible resistor on the power supply board that will be open. This resistor is, I believe, a .1 ohm, 1/2 watt. All of these parts are available as a kit from a number of TV supply houses (electronix, MAT electronics, etc). After you replace these parts, resolder the connections on the horizontal drive transformer. That's the little transformer that the base pin of the horizontal output transistor connects to. It might also be a good idea resolder everything around the flyback and horizontal output transistor. Loose connections are generally what shorts the HOT; which, in turn blows the transistors and the resistor in the power supply. If the new parts blow up after resoldering the connections; you most likely have a bad flyback.

kx250rider · #3 11-13-2007, 10:58 AM

Radiotvnut is right... And there are 3 VDRs that need to be changed, but I'm sure they're in the kit. The fusible resistor is R602, I think. Facing the back of the TV, it's right on the far edge of the board near the left. It's white ceramic, and is phyisically bigger than a regular 1/2 watt. The transistors are 2SC4834MN.

Caution: That TV is famous for having a weak picture tube.

Charles

YamahaFreak · #4 11-13-2007, 11:21 AM

Quote:

Originally Posted by kx250rider

Radiotvnut is right... And there are 3 VDRs that need to be changed, but I'm sure they're in the kit. The fusible resistor is R602, I think. Facing the back of the TV, it's right on the far edge of the board near the left. It's white ceramic, and is phyisically bigger than a regular 1/2 watt. The transistors are 2SC4834MN.

Caution: That TV is famous for having a weak picture tube.

Charles

Does that mean I'll end up having to replace the CRT, or is there a way to rejuvenate it? And do they all get weak after 14 years? I'm not sure how much the previous owners used the set, but judging by the amount of static-induced dust, I'd say a lot.

EDIT: Wouldn't that be 'infamous'?

radiotvnut · #5 11-13-2007, 12:08 PM

Yes, I think electronix has the kit that contains the VDR's. It's about $12 I think. And yes, those CRT's tend to go weak. I have a B&K 470 rejuvenator and there was never a socket made for that set. I finally made one from a socket taken from a junk board. B&K does make a "universal" adapter that is nothing more than clip leads attached to a socket that plugs into the tester. B&K is very proud of this adapter. It was just easier (and cheaper) for me to make the adapter to fit the tube. I always like to check the CRT in sets before I work on them. It's very upsetting to spend a lot of time on a set just to discover a weak CRT; and, that's what I did a few times on the Sony's before I made the adapter.

A year or so ago; I found two identical '90 27" Sony's (from different people). Both had high hours on them. One still had a very good picture. The other was watchable; but, it was obvious the CRT was weak. If you don't have a CRT tester; you'll just have to take a chance with the parts and hope for the best.

YamahaFreak · #6 11-14-2007, 04:29 PM

Quote:

Originally Posted by radiotvnut

Yes, I think electronix has the kit that contains the VDR's. It's about $12 I think. And yes, those CRT's tend to go weak. I have a B&K 470 rejuvenator and there was never a socket made for that set. I finally made one from a socket taken from a junk board. B&K does make a "universal" adapter that is nothing more than clip leads attached to a socket that plugs into the tester. B&K is very proud of this adapter. It was just easier (and cheaper) for me to make the adapter to fit the tube. I always like to check the CRT in sets before I work on them. It's very upsetting to spend a lot of time on a set just to discover a weak CRT; and, that's what I did a few times on the Sony's before I made the adapter.

A year or so ago; I found two identical '90 27" Sony's (from different people). Both had high hours on them. One still had a very good picture. The other was watchable; but, it was obvious the CRT was weak. If you don't have a CRT tester; you'll just have to take a chance with the parts and hope for the best.

Any idea how much that kit will cost?

I'm going out to look for the parts mentioned in the PS.

radiotvnut · #7 11-14-2007, 04:48 PM

I think www.electronixonline.com has the kits for around $12.

YamahaFreak · #8 11-14-2007, 05:10 PM

All right, I got the part #'s of the components. Please excuse my horrible photos; they were taken at an odd angle.

Tell me if I got the parts right:

http://img218.imageshack.us/img218/5...20777idnf4.jpg

http://img134.imageshack.us/img134/1...20778idcu5.jpg

EDIT: I will need some help locating the horizontal drive transformer. My guess is that it's the small one with yellow tape on it in my photos, but I'm not sure.

EDIT AGAIN: In one of the pics, I've accidentally reversed the PS transistors' part numbers; Q601 is closest to the large power supply caps.

YamahaFreak · #9 11-14-2007, 05:13 PM

Quote:

Originally Posted by radiotvnut

I think www.electronixonline.com has the kits for around $12.

Would this be the correct one?

http://www.electronix.com/catalog/pr...ducts_id/13024

Also, I've noticed that the "racetrack-shaped" speakers, to quote Kiwick, have rotted surrounds. I'm guessing it will be a royal PITA to find replacement surrounds, so I'll probably just pull some similar oval speakers from another set. Shame though, because they are nice speakers. 5 watts with huge magnets and stiff spiders.

Sorry for so many posts/questions; this is my very first serious television repair.

YamahaFreak · #10 11-16-2007, 02:07 AM

I was actually able to move the set inside(yes, it's been sitting in the backyard under a tarp for the last three days!

) This allowed me to take some MUCH better photos. Just to make doubly sure the problem is what I think it is, I got out my DMM and tested the fusible resistor. It is indeed open. I am wondering if I could get away with just replacing the resistor, or if it would just blow up again?

Worth noting IMO is the way Sony designed this set for simple and easy repairs. All the boards are letter-coded and all instructions for service procedures, carrying the chassis, service positions, etc. are all listed inside. I like it, especially since this is my first serious repair!

Behold, better pictures!

The first photo was taken from the left side of the set, and marks key components:

http://img340.imageshack.us/img340/3461/1020779fx5.jpg

The second was taken from the rear and is larger and unmarked to show detail:

http://img211.imageshack.us/img211/7859/1020780ja2.jpg

Again, I apologize for repetition of posts.

vinyldavid · #11 11-16-2007, 02:17 AM

I never had any trouble with my Sony 27" Trinitron until I gave it away, and it is at a friend's house and he abuses it, but it still works as good as the day it was manufactured. made ?April? 1994.

3Guncolor · #12 11-16-2007, 09:05 AM

If you change just the fuse good chance it will just blow again. Check Q601 and 602 for shorts. The transformer you listed as the horiz output is really part of the powersupply it is part of the driver system for Q 601 and 602.

After you test the parts in the power supply you need to make sure there is nothing else wrong with the set. I would at the very least check the Horiz. output for shorts. Also you must check the horiz driver transformer for bad connections.

If you don't find the cause of the power supply problem it will just blow again.
Also its a good idea to test the set at reduced voltage less chance of plowing up the replaced parts that way. After the set powers up then you can go to full power. I have used around 70 volts A/C for this.

YamahaFreak · #13 11-16-2007, 03:09 PM

Quote:

Originally Posted by 3Guncolor

If you change just the fuse good chance it will just blow again. Check Q601 and 602 for shorts. The transformer you listed as the horiz output is really part of the powersupply it is part of the driver system for Q 601 and 602.

After you test the parts in the power supply you need to make sure there is nothing else wrong with the set. I would at the very least check the Horiz. output for shorts. Also you must check the horiz driver transformer for bad connections.

If you don't find the cause of the power supply problem it will just blow again.
Also its a good idea to test the set at reduced voltage less chance of plowing up the replaced parts that way. After the set powers up then you can go to full power. I have used around 70 volts A/C for this.

Would I just use something like a DMM for checking the transistors? And what setting? I kinda figured that wouldn't be the HOT. Do you know which one it is, in addition to the horiz. drive?

EDIT: Actually, I think THIS is the proper kit. I am ready to buy; just making sure I get the right one!

http://www.electronix.com/catalog/pr...oducts_id/6557