Riddled TV Repair Forum

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

Let's back up to the power supply. Measure voltage across D825. Also D809 Cathode (line) to COLD Ground. (130V and 18.3V)

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chumba · Joined: 01 Jul 2009 Posts: 66

With HOT removed and pressing power button ON,
V across D825 = -9.4 v with -ve to stripe (cathode), and +9.5 v to either hot or cold ground.
D809: With -ve lead to Cold ground and + to stripe side: V= -95 mV, and +95 v to hot ground, (and -28 mV across it).

T502 also has +95 v between all pins & hot ground.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

When you plug set into 120VAC, do you hear a relay click each time you press the power button? (1st press relay energizes - 2nd press relay releases).
Raw B-Plus: Red DMM lead to positive side of C805, while Black DMM lead to negative side of C806.
Approximately 300V?

chumba · Joined: 01 Jul 2009 Posts: 66

B+ reads +329 v @ C806 when measured as described.

I only hear relay click once when plugged in & again when un-plugging, NOT when power button pressed. If the TV sits unplugged overnight, the 1st time I plug it in there is no click but a short whine like the CRT is trying to come up---but this happens only once, then goes back to the same clicking.
(HOT is still removed, but same click behavior with or without HOT)

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

I was a little confused by your terms for meter leads... Is this correct? +ve = Red (positive) / -ve = Black (negative).
You (I believe) are/were confused by the set having Cold and Hot grounds?
Ground is (usually) where you put the black meter lead for most measurements.
This set uses HOT ground for horizontal deflection circuits and Switched Mode Power Supply secondaries (130, 29 and 18.3 volts {18.3 volts is reference COLD ground}).
COLD ground is used for stand-by and scan-derived power supplies. (Q002 collector = 11.1volts & emitter = 5 volts).
So far I'm only sure that you have Raw b-plus.

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chumba · Joined: 01 Jul 2009 Posts: 66

Yes, I've been using the abbreviations +ve = Red (positive) and -ve = Black (negative). At the start I was confused b/w hot & cold grounds but after you explained it, all the measurements were taken that way - i.e., cold ground=chassis ground=CRT screw=tuner case, and hot ground=-ve lead of C806=heat sink of HOT...correct?
This way I measure:
Q002 Collector= +9.4 volts, Emitter =+5 volts, Base = +5.6v.
I also measure Q801 to hot ground: VC= +8v, and 0v on B & E.

Do you have a svc manual or schematic you could point me to? It seems like something is hosed in the step down circuit between the raw B+ & the drive to the HOT because I dont measure ~+130v anywhere, closest is +95v at T502 secondary.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

FOR NOW LET'S STAY IN THE SMPS PRIMARY!

chumba · Joined: 01 Jul 2009 Posts: 66

Q801 & Q802 measure +9.4 v on all 3 leads to hot ground.
Also, correction, Q501 Collector meaures +8 v to hot grnd, 0 on B&E.

IC803 voltages to hot grnd measure:
Pin1: +9.5 v
2: 9.5 v
3: 327 v
4: 9.4 v
5: 9.4 v

Q001 - is this the small surface mount transistor on the bottom of the pc board? If so I measure +3.4 v @ Base only when plugging the power cord in, but no change when pressing power button.
(no voltages on other 2 pins to cold grnd).

I don't see any other cracks but will keep looking.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

Check resistance across D825 (130V) & D830 (18.3V) - Resistance reading should go "upity-upity-up." If no loads on those lines continue...

You DO have the stand-by supplies and Raw B-Plus.
Have you determined the conditions of Q001; Q801 & Q802?

Check the following parts (if necessary pull one side and check out-of-circuit): D820; D821; D822; D823; D824; D826 & D829. Also: R822; R824; R826; R827; R828 & R829. If ALL test O.K. Change IC803. If ANY test bad (or before applying power after changing IC803) - report.

chumba · Joined: 01 Jul 2009 Posts: 66