Toshiba CRT projection TV chassis TAC9855

[radiotvnut]

A friend found a '98 Toshiba rear projection TV on the curb and ask me to fix it if it can be done very cheaply. I've always hated working on this type of TV and swore years ago that I'd never touch another one; but, I told him I'd look at it. The problem is that it comes on very bright with retrace lines and then goes into shutdown (like what regular CRT sets do when the 200V supply to the video output stage is lost).

Working on this set, I'm reminded why I hate working on them. The wires on the chassis are not long enough to easily pull the chassis and flip it over for servicing. So, I had to disconnect most cables in order to get the chassis out so that I could flip it over. Of course, with everything unplugged, I can't fire up the set to take voltage measurements. And, laying on my stomach to work on it doesn't help much.

Does anyone have a service manual or any advice for this set? I don't plan on spending a lot of time on it and I'll probably end up making him pick it up and take it back to where he found it.

[zeno]

I didnt do many projo's myself but I think on later Tosh
the chassis & tubes cam out as a unit to work on.
Also no reason not to check the 200v at the collector resistor
on one of the jugs. At 15 yrs old odds are at least one tube is soft
if not all & it will look like dog doot.......
Other advice ? Stick with DV sets, I detested projections for both
watching & fixing. Not to mention people kept them too long
just like the old console days, they just wouldnt listen.
Good luck

73 Zeno

[radiotvnut]

OK, I checked some voltages and it's not looking too good. I have 204V on the input of the collector resistor on each video output transistor; which, seems OK. When I move to the collector side of the resistor, I have 7 volts; which, is not good. This voltage is present on all three video output collectors, regardless if the socket is plugged into the CRT or not. Moving to the base of each video output transistor, I measure about 8 volts; but, when I check the resistance from the base of each video output transistor to ground, I read around 212 ohms. In direct view TV's of this age, I seem to remember the base of the video output transistors getting their drive directly from the jungle IC and I don't believe I should be getting that low of resistance reading from the bases of the transistors to ground. At this point, I'm leaning towards a leaky/shorted jungle IC. I even tried turning down the three master G2 controls, in hopes that it would dim the CRT's enough that it wouldn't trip the protection circuit; but, no luck. The way I measured voltages was to clip my meter to the desired test points and then I powered up the set. I'll probably end up scrapping the set if it turns out to be the jungle IC.

[zeno]

Originally Posted by radiotvnut

OK, I checked some voltages and it's not looking too good. I have 204V on the input of the collector resistor on each video output transistor; which, seems OK. When I move to the collector side of the resistor, I have 7 volts; which, is not good. This voltage is present on all three video output collectors, regardless if the socket is plugged into the CRT or not. Moving to the base of each video output transistor, I measure about 8 volts; but, when I check the resistance from the base of each video output transistor to ground, I read around 212 ohms. In direct view TV's of this age, I seem to remember the base of the video output transistors getting their drive directly from the jungle IC and I don't believe I should be getting that low of resistance reading from the bases of the transistors to ground. At this point, I'm leaning towards a leaky/shorted jungle IC. I even tried turning down the three master G2 controls, in hopes that it would dim the CRT's enough that it wouldn't trip the protection circuit; but, no luck. The way I measured voltages was to clip my meter to the desired test points and then I powered up the set. I'll probably end up scrapping the set if it turns out to be the jungle IC.

Look up the jungle ( TA????). Find the VCC pins & measure them.
There are prob. 3 or 4 of them. Check both DC & ohms.
Maybe a B+ line is out from FBT or main supply. Usually when
a jungle shorts you will see it on one of the VCC's. (ohms).
It will also get HOT not pleasantly warm. If you can prob.
keep the set running by pulling all 3 CRT skts.
Shut down circuit is seeing too much beam current.
IC prob. cheap, if your pal wants to gamble.........

73 Zeno

[radiotvnut]

Haven't had much time to devote to this set; but, I have determined that the problem is ahead of the CRT sockets and I'm very sure it's the jungle IC; which, is installed on a plug-in stand up module on the right of the chassis.

The owner has indicated that he doesn't want to spend much on it and has actually already tried to give me the TV, saying that I could fix it and sell it. I told him that I couldn't give it away if it worked perfectly. I added that I didn't have a way to easily dispose of it and I expected him to pick it up, regardless if I fix it or not.

If I wanted a large screen TV, I'd break down and get a flatscreen over wasting time and money on a large, bulky, worn out projection set that didn't look that great when it was new.

[Geoff Bourquin]

I don't have a service manual handy, but if this set has a hyperboard, I would guess that's where the trouble is. I know they used them in 2000, don't remember if they had it yet on '98 models. I used to see those things die all the time. Usually a bunch of bad SMD capacitors die. Repairable, yes. A pain, also yes