[TechAssist] progress! got reset back! RCA ATC113CA1, F36444 still dead. subbing a Gemstar module as test?
- From: Phil Bader <tjanphyl@xxxxxxxxxxxxxxx>
- To: "techassist@xxxxxxxxxxxxx" <techassist@xxxxxxxxxxxxx>
- Date: Wed, 06 Jul 2005 12:17:40 -0400
Progress! I got my reset 5VDC to the Gemstar back
(yes I have a Sams#4855 on disc)
Decided to tackle the reset issue again. I lifted the reset line from
the gemstar. The board side of the disconnected line stayed low (.5V).
Started checking around those transistors (TR521,523) Collector of TR523
is being pulled low for no reason, Collector pad voltage low EVEN with
TR523 unsoldered and removed!. I measured 2K ohms from collector pad to
ground. No way, there's no path that low. (gemstar pin still
disconnected)I finaly unsoldered SMD cap CR541 (.01uf from collector of
TR523 to ground. Now the resistance to ground shot up to 25K ohms. The
cap didn't measure short in my trat, so I guess maybe the glue?. I
replaced it with a tiny standard .01 cap, soldered TR523 back on the
board, my 25K resistance stayed. Plugged it in, and my reset pin now has
5VDC!
But, still no start up when power pushed, but progress!
Now maybe I will redo those gemstar tests again.
Phil Bader
Philip Bader
Jan Phyl TV Inc. (estab. 1976)
3420 Recker Hwy. Winter Haven, Fl. 33880
Fax (863) 299-8821
email: tjanphyl@xxxxxxxxxxxxxxx
Wayne Lasalle wrote:
>There may be some slight differences in or manuals, let's go closer to the
>circuit in question.
>You mentioned TR521 and TR523 are turned on.
>These two transistors seem to form a latch (Tr521 is a PNP transistor and
>TR523 an NPN.
>The base is of TR521 is biased by the
>Divider RR563 and RR564 1% resistors so it's critical.
>According to my manual, the base of TR521 should be 5.8V and the Emitter
>5.3V and the collector to ground.
>If the base of TR521 fall .6 volts below the emitter its going to turn on
>TR521 once it turns on It will feed the emitter supply to the collector
>through rr568 to the base of TR523 this effectively grounds the collector of
>TR523 which pulls the base of TR521 down and thus latching up the two
>transistors.
>I'm still not sure yet but this may be the reset circuit it self.
>If it is, they should turn on for a second then turn off again.
>That would mean that RR567 27K 2% may help to pull it out of the latch
>condition and create a reset pulse.
>I would be very suspicious of RR567 or TR523 could be shorted.
>Check the transistors for shorts and let us know.
>Wayne LaSalle
>Upstate Electronics
>serving central NY
>
>
>
>
>-----Original Message-----
>From: Phil Bader [mailto:tjanphyl@xxxxxxxxxxxxxxx]
>Sent: Wednesday, July 06, 2005 9:38 AM
>To: wlasalle@xxxxxxxxxxxx
>Subject: [Fwd: RE: [tv-repair] RCA ATC113CA1, F36444 still dead. subbing a
>Gemstar module as test?]]
>
>Not sure if you "typo'd" "CP350" (can't locate) for the +16 V source.
>The only 16V source I find in my Sams originates from rectifier diode
>DP63, filtered by lytic CP66, goes thru resistor RP350 (3.3@2W) thru
>coil LP350. This has a junction of diode DP350 anode. The +16 volts at
>this source is OK. (don't see where it goes to the reset ckt,tho)
>As far as the output of the IP350 pin 3, 5.2V reg IC, it measures +5.3
>volts, and is present.
>Phil Bader
>
>-------- Original Message --------
>Subject: RE: [tv-repair] RCA ATC113CA1, F36444 still dead. subbing a
>Gemstar module as test?]
>Date: Tue, 05 Jul 2005 20:29:26 -0400
>From: Wayne Lasalle <wlasalle@xxxxxxxxxxxx>
>
>
>I think you're closing in on it.
>
>Those two transistors seem to be a latch circuit.
>
>See if you have the 16 volts off the switch mode power supply at cp350. If
>it's absent it looks like it would trip the latch.
>
>Also check the output at IP350 pin 3 (5.2 volt regulator.)
>
>Wayne LaSalle
>
>Upstate Electronics
>
>serving central NY
RCA ATC113CA1, F36444 still dead. subbing a Gemstar
>module as test?]
>
>
>
>I scoped the eeprom. Pins 5,6 do not ever have data. pin 8 has the Vcc OK.
>I went down the gemstar, so far the DC voltages are OK (have not
>finished yet) but one main thing: The RESET pin (BR104 pin 7) to the
>gemstar should be +4.7VDC. It's low, at .5VDC (half-volt). The two SMD
>transistors seem OK (TR523,521) But seem to be turned on for some
>reason., hence the 4.7v is being dragged down. I am not strong in
>digital, but this is significant. Yes? I hung a scope set to DC (5V per
>div) and plugged it in while watching, and no change.
>Phil
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