[TechAssist] Re: RCA 27" TV mod. F27701BK, chas. CTC169CA6 won't start
- From: "drcvr" <drvcr@xxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 17 Oct 2002 09:23:14 -0400
Hello Gary!
Look at near the end of TA8680N, if you see it looks wet around Y301 (50 KHz
horizontal pulse generator crystal) change that Y301 and C3810(16V 33uF).
Electrolites get into Crystal.
HTH
Don B.
Dr. VCR est:1994
20 Hanson Ave
Kitchener, Ontario
CANADA N2C 2E2
Tel 519-579-7112 Fax 519-579-1996
drvcr@xxxxxxxxxx
----- Original Message -----
From: "Gary McCartney" <number63@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, October 16, 2002 11:44 PM
Subject: [TechAssist] RCA 27" TV mod. F27701BK, chas. CTC169CA6 won't start
>
> This is a real headache set. I'm not even sure I can explain the problem
> or what all I have tried well enough but I'll give it a shot.
>
> The set is an RCA 27" TV mod. F27701BK, chas. CTC169CA6. I am using the
> service manual for the CTC169 projection chassis.
>
> Set came in with complaint that it wouldn't come on. I plugged it in and
> it started up with picture but the HV would have the odd pulse for a
> brief second then it would be ok for a couple seconds, then the same
> thing again. By pulse, I mean that the HV would start to dissappear but
> would come back up before picture went all black.
>
> I measured the 143V B+ and it was pulsing down to 133V, so I went ahead
> and replaced parts in the regulator circuit: U4101, the 3 small caps
> around it, CR4122, CR4118 and it's filter cap. Then I adjusted the B+ to
> a stable 142V. Cathode of CR4118 measures 13.5V. Somewhere along the
> line, I lost picture (raster)and sound even though the HV was still
> there. The HV was still pulsing a bit. I measured the HOT collector
> waveform and it looked great but would dissappear for a brief second
> when the pulsing occured. Traced the hor. pulse all the way back to the
> TA8680N jungle chip where it was pulsing there too.
>
> Then I checked the micro for TV-on voltage output at pin 38. It also
> pulses high then low. The reset pin at pin 1 checks in at 4.5V but dips
> to 3.3V when the pulses happen. Pin 19 B+
> stays at 4.78V all the time. The pulsing appears at the ON-OFF
> transistors Q4306, 4304, 4301, 4705 and 4305.
>
> Now when I press power-ON, I get a square wave to the hor driver base
> but not on the collector. I have tried a different transistor and a
> different hor. driver transformer. Also, the B+_ on the driver collector
> is at 12.93V, then pulse drives it to zero volts for a second, then back
> to 12.93V again. I replaced the HOT, then I tried a 100W light bulb from
> the collector to ground (with the flyback not connected to collector).
> Still nothing has changed. I get the 7V source and it is always there.
> All the run source voltages are not there. The 143V B+ stays at 142V.
> The 15V sorce is at 13.5V but dips to 12.3 when the pulse occur.
>
> I have replaced the Q3102, Q3101 rest transistors, plus C3124 off pin 38
> of micro. Also tried C4141, U1001(TA8680N, another micro IC( although
> it's physical pins could be in better shape so I'm not 100% sure that
> chip can be trusted), plus the eeprom. Changed R4314 39 ohm resistor
> feeding 15V B+ to hor. driver collector because it looked a bit off
> color. Removed the two interconnect cables from the audio circuitry and
> removed R4544 on 26V line to vertical IC.
>
>
> I must be missing something major here. Any help appreciated
> --
>
>
>
> Gary McCartney
>
> McCartney Electronics
> 7134 Fife Rd, RR 7
> Guelph Ontario Canada N1H 6J4
> Fax: (519)821-1530
> email: number63 (at) inetsonic.com
>
>
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