Zenith TV 25GC45 Requesting Advice

[VTRadio]

Zenith 25GC45 owned since new. Went off-line yr. 2001 or so. Stored in dry basement for 23 years. Trying to get TV functioning again.

1. Set was completely dead. Breaker tripped. Reset breaker, set still dead. Don't remember if it had lit CRT filament.
2. No smell or charred components.
3. Pulled Horiz. power transistor.
4. Pulled wires off of oil cap. Not shorted. Powered up set still dead. Reconnected oil cap.
5. Checked diodes on 9-123 board all good.
6. Voltage regulator transistor good.
7. Has orange drop twin cap. HV safety upgrade.
8. Have tested "source" voltages as identified in SAMS document. Anomily noted - 125v source measures 136v and 130v source measures 140v.

Note: Have SAMS Set 1558 folder 2 and Zenith CM-124S1 service documents.

Current state. NOTE:Some of the results don't make sense.
I pulled the diodes CX201 CX202 from pin 6 of 9-123 board and powered up set. Got audio. Pulled the 9-92-C board and reconnected diodes. Set audio came up. Placed 9-92-C board back in place. Saw fuse FX203 next to vert. board flash open when set powered up. Still have audio. Vert. brd 9-92-C board pins 9 and 11 appear to connect to fuse FX203. Pins 9 and 11 measure 6.30v instead of -.14v and pin 21 measures 4.83v instead of .41v as per SAMS document. All other voltages close to SAMS doc.

Note: Horiz power transistor removed from set.

Have experience with vacuum tube radio and amp repair and restoration but little experience with semiconductors and no TV experience.

Requesting advice what next steps to take.

Thanks

[zeno]

1) be sure the 4 lead cap is in right. I assume you used an 800-860 kit
Two of the wires cross over each other. One pair completes the
HOT collector path & the other two the emitter path. Either can open & kill
the HV. Thats the safety part if it.
2) audio will work with just the 24 VDC
3) after the HV is up go to vert. Best to upgrade the 9-92 to a
9-147. Much better board. Only use EXACT value fuse !
4) The high B+ is either due to no load OR open oil cap. The set will run
with it open but be unstable, pulsating etc. They are going left & right
now, at 45 yrs +, but in the day not so commonly ....

Good luck
Zeno
LFOD !

[VTRadio]

Thanks for your response.

[VTRadio]

Trying to figure out downstream circuitry from Vert board 9-92 and .6amp fuse fx203. SAMS tells me the next item is sw201 and then on to the vertical deflection coils. Zenith tells me its sw201 and then on to the video module 9-89. Double checked chassis numbers between SAMS and Zenith and the numbers match (25GC45). What am I missing?

Thanks

[VTRadio]

Spent a bit more time with SAMS and Zenith documentation and figured out why they initially appeared to be different. A couple different ways by a couple different entities to present the same circuit design. Can see benefits and issues with both methods.

[VTRadio]

Obtained original Zenith 136-114-13 replacement fuses. Also located and obtained similar fast acting Buss 0.6amp fuses for testing. Powered up the set with conv yoke and defl cables disconnected at chassis. Used both an original Zenith fuse and a later day Buss equivalent fuse. Fuse did not activate. Reconnected both cables. Tested with both fuses and none activated. Ran a resistance test of both fuse types. The original Zenith fuse, subtracting lead resistance, indicated 1 ohm resistance. The Buss replacement fuse indicated .5 ohms resistance. Went through both boxes of fuses with same results. At 1ohm, measuring voltage drop across Zenith fuse in circuit might give some indication of amperage across fuse.

The only component missing from the circuit now is the Horizontal output transistor. Will test and inspect and if good will reinstall transistor.

By the way. I also have a 1976 Zenith 19" portable TV 19GC45Z1 with a similar circuit design and many identical parts. Used it in resistance testing between vertical sections of both sets. Found results to be very similar.

[zeno]

Note. IIRC both the yoke & 9-90 boards are interlocks for the
130 V line. This varied over the yrs.
SW201 is probably the service switch. On main chassis.
Kills both video & vert to set grey scale.
Many small parts were the same from B line sets to L line sets,
apx 11 yrs. Millions were sold, probably more than any other color world wide.

Zeno

[VTRadio]

Thanks for this information.