View Full Version : 1982 Sears Channel Touch 19" model 562.42181250 issue


pac.attack76
06-12-2016, 11:13 AM
Picked this up the other day. Tested and came on for about 2-3 see ones with sound then immediately off with no sound and the rainbow colored spots on the screen that take several minutes to go away. Turning it off and back on lasted maybe a second and right back off with the same colors on screen. I've never seen anything like this before. Anyone know what's going on with this one?:scratch2:

zeno
06-12-2016, 01:27 PM
Sounds like HV shut down. See if it works on variac at
abt 100V. Watch the current, dont let it go above apx
one amp. It will draw a lot more for a second when cold
then fall back.
If it dont try starting it a few times then see if
the hoz out transistor is getting hot. Nudies please !

73 Zeno:smoke:

pac.attack76
06-12-2016, 04:36 PM
Sounds like HV shut down. See if it works on variac at
abt 100V. Watch the current, dont let it go above apx
one amp. It will draw a lot more for a second when cold
then fall back.
If it dont try starting it a few times then see if
the hoz out transistor is getting hot. Nudies please !

73 Zeno:smoke:

Don't have a variac right now. Working on getting one tho. Anything I can try right now? Nudies?:D

radiotvnut
06-12-2016, 05:43 PM
You really need a variac to troubleshoot this problem and there are several things that can be causing it.

1. Voltage regulator circuit in the power supply is defective. Typically, the B+ voltage in '80's and newer solid state sets is in the 120V to 130V range. If the voltage regulator circuit fails, B+ can rise to 150V-160V and this will also cause the HV to rise. When this happens, the HV shutdown circuit is triggered and this kills horizontal drive. With a variac, you can attempt to power up the set at 90-100V, while monitoring the B+ voltage. If the set stays on at 90V, gradually raise the AC input voltage and watch the B+ voltage. If the B+ voltage starts creeping up as you raise the AC input voltage, you have a voltage regulator problem. Voltage regulator issues are usually caused by the regulator IC itself, or any resistors or capacitors associated with it.

2. The power supply may be OK; but, there could be a fault in the horizontal output stage that is causing the HV to ramp up and trigger the shutdown circuit. The most common cause here is the capacitors that connect between the collector of the horizontal output transistor and ground. By the time these sets were made, these capacitors were usually either disc or film capacitors; but, I have seen them open and they can drift in value. They can also drift in value after the set warms up.

3. Loss of horizontal drive. This could be due to poor solder connections on the horizontal driver transformer (not the flyback - the little small transformer in the horizontal circuit) and/or the horizontal driver transistor. I recall working on one older Sears set that was doing what yours is doing and it was a bad horizontal driver transistor; but, the transistor didn't check bad with a meter. My theory is the transistor was good enough to allow the set to come up for a couple of seconds. Then, it would break down under load and kill the set. Also, any electrolytic capacitors in the drive circuit should be checked/replaced.

pac.attack76
06-12-2016, 07:41 PM
Thanks for the tip. I'll get one of those variacs as soon as I can. Then I can find out for sure. I'm wondering if it is number 3. It'll run for a couple seconds and with the load, it'll kill out.

pac.attack76
06-15-2016, 08:54 PM
Ok, here's the inside. Couldn't find anything burned, cracked, or blown.

radiotvnut
06-15-2016, 10:18 PM
That's a rebadged Toshiba.

Findm-Keepm
06-16-2016, 09:44 AM
From Dad's handwritten Sams notes:

Horiz Drive Xfrmr - intermittent open secondary. Heat the pins to cure.
Film caps near fly - 2400pF/2700pF/3300pF - out of tolerance, causes shutdown.

Also, once it's going - lots of vertical notes for this set - caps, caps, caps, and one for the chip. "see also Toshiba CF19 and CF20-series sets for remote stuff."

Not all notes are my Dad's - he loaned out Sams to other shops, so YMMV.

Cheers,

Username1
06-16-2016, 10:11 AM
Radiohut has set out a good plan of items to check on this tv. 80's power supplies almost
always required a startup with a variac, I know that is what we used ours for, not much
else..... It's a question of what is causing the shut down. Since HV had a shut down
circuit, that is pretty much what is turning it off, but B+ too high caused HV to go too high
so the HV shut off the tv. You have to figure out the PS first. If it's ok, go on to the
rest of it..... Also if your dad changed out a few caps, then it's possible they are
bad again.....

.

zeno
06-16-2016, 11:02 AM
Major points are

Hoz out in front of yoke plug
hoz drive transf to left of h out
hoz drive transistor to the left of it.
LV regulator on black heat sink with model tag.
Vert outputs are 2 transistors on small sinks
near hoz drive

If you got a HV probe see how much its coming up.
If not you can do the same thing at the 200V.
Go to CRT socket. There are 3 larger resistors same
value. where they join is the 200V. See how much
it comes up. That gives an idea of the HV level.

73 Zeno

pac.attack76
06-16-2016, 11:44 AM
Check to see how much comes up as soon as I turn it on? I probably won't have very long as it only runs about 2 or 3 seconds.

zeno
06-16-2016, 03:28 PM
Check to see how much comes up as soon as I turn it on? I probably won't have very long as it only runs about 2 or 3 seconds.
Thats all you need.
I am bugging out for the weekend, going down Maine.
Catch up on Mon & will pull the Sams if I got it & you still
need help.

73 Zeno:smoke:

pac.attack76
06-16-2016, 05:37 PM
Thats all you need.
I am bugging out for the weekend, going down Maine.
Catch up on Mon & will pull the Sams if I got it & you still
need help.

73 Zeno:smoke:

No problem. Talk to you then.

pac.attack76
06-20-2016, 09:27 PM
Set went in the trash today. Too far gone fore me to bother with. Keypad was bad as well.