Initial D Version 3 Question

[grantspain]

i have no idea, i only ever had this with caps wrong value voltage or if installed wrong polarity

[Zorigami]

Is there any harm in my trying a new cap (I have 4 more freshies from my local electronics shop) in the reverse direction just to see?

If the worst case is one more blown cap then maybe it’s worth a shot?

Also, on maybe 3 caps including c824 and c836 I got lifted pads when I pulled the old caps off. The copper didn’t break off of the trace, just became . . . Unglued, i guess, from the PCB. I did my best to secure them when I soldered the new caps. I also checked continuity for all my caps and am certain that they are connected with the other components on their respective traces (tested the legs of the new caps to nearby non-replaced components for every single cap I replaced).

Could that be part of the problem? And would jumpering them (the lifted pad components) to something else on the same trace on the solder-side be useful?

[Zorigami]

With nothing to lose, I reversed the polarity of the replacement cap at c830: new cap, negative lead to the right instead of to the left like the board masking indicates.

Powered it up and c830 didn’t explode! C822 did.

Took a bit longer but still a catastrophic failure. Fortunately, the installed cap at the time was the old one so I still have a new one to try later.

Left with this question: should I replace 822 with a reversed cap, or reverse 438 (first cap in the circuit, I think) and set both 830 and 822 to the correct orientation? Some other plan?

Man do those KSC caps smell unpleasant when they pop.

[grantspain]

well i would not have tried that as your polarity's were all correct
do me a favour take photos of all the areas where you changed caps and note the values - only power section and deflection section

[grantspain]

what was your original fault btw?

[grantspain]

check q407

[Zorigami]

Originally the problem was that the corners of the monitor were pretty blurry and I was moving the monitor from one cab to another. I figured Since I had everything apart I’d re-cap it prophylactically.

I have put all of the caps back in their board-directed orientation as of this morning. I have also jumpered the loose pads at c284 pad pos (to L811 and A86) and c826 pos (to r831 and l813). Continuity checks on all of that are good and the respective caps are much more secure.

I plugged it in and I didn’t get any explosions today, but I’m getting no heater voltage/neck glow now. The chassis is making regularly irregular clicks though, so there is some life.

Pulled q407 (the HOT, right?). All tests performed with the flat side down on my bench. The only reading I get is 0.56 with pos in the middle and com on the right. I’m guessing that this is an NPN transistor and also: fried.

After checking the the sheet for a j512 mosfet I’m only getting a reading with pos on the drain and neg on the source. No other combination of pins and leads gives a reading.

My local shop has NTE2990 mosfets in stock (p channel,
250v 6a). Would that work to replace the j512 (p channel 250v 5a?)

[grantspain]

take it out and read on diode test

[Zorigami]

Desoldered it and measured it on my bench. The only reading I got was pos on the middle leg (#2 per the data sheet: the drain) and neg on the right leg (#3: source). Reading was 0.56. No other combination of leads and legs gave a reading.

[grantspain]

that sounds correct to me

[Zorigami]

Correct as in not broken and functioning normally?

Or broken and malfunctioning in the way you anticipated?

If not broken, next step is to check the flyback?

[grantspain]

seems correct reading
check value of r488, may find two resistors there and should read 16 ohms or near
check value r431 and it should be 4.7 ohms

next step isolate centre pin of q417 and add 40w lamp to the track of that pin and ground and then check b+ is 180v

[Zorigami]

R488 (and its twin r487): 15.3 ohms
R431 - dead. No resistance reading, no continuity

[Zorigami]

To be certain, I wanna post this monstrosity before I plug it in.

I have a 40w bulb soldered to the middle leg of q417 (cleaned it of solder as best I could and made sure it had no continuity any more) and then screwed into the chassis ground.

597EB3FD-2F3C-44B5-8632-F3C3B1844592.jpeg

ED2D8DE6-110D-4492-9159-B16B9C47A20A.jpeg

Plug in this beast and measure b+ where? On the neck board where the 2nd line goes from the flyback?

C1F51E8A-2A31-4A5C-9753-68DC89635ABA.jpeg

[grantspain]

nope, the lamp needs to be on the track of the pin and not the pin- probably best off removing the transistor to be safe
make sure you replace r431, its a metal oxide 4.7 ohm 1 watt safety resistor

read the b+ at c830 +

[Zorigami]

Ok, hopefully this is the jam:

[Zorigami]

Does the anode cap need to be plugged in, or can I bench test this? Easier to measure the solder side of the chassis if it isn’t in the cabinet

[grantspain]

yes,now if you power on you should get a steady glow from the lamp and the b+ should be solid at 180

first power up just make sure the lamp lights up for a few seconds, read b+ at next power up

you can do all this with the chassis on a bench disconnected from the tube, being wary not touch anything on the chassis with your bare hands of course

[Zorigami]

Damn. Chassis clicks on, no glow, no voltage at c830

[grantspain]

now you have to isolate further back on the chassis, lift link A20 and add the lamp to the A19 link