K7000 medium res (paperboy) dead

Did you pull those resistors out of the board and check them again? A lot of times you'll get a funky reasding in the board if the part is in parallel with something else, like the flyback....
 
shardian said:
Finished the rebuild today, put it all back together and fired her up.

Nothing on the monitor still. Wow...that sucks.

At this point, I'm not even sure where to go. What is that white thing that is bolted to the frame, off to the side of the chassis? Seems power runs through it.

Any recommendations? I repaced all caps, flyback, HOT, regulator, desoldered/cleaned/resoldered suspect connections, including the 2 large resistors.
Click to expand...

If B+ is ok, replace IC2 (la7823)
 
I pulled this out again tonight, because I am under orders from the wife to get her Paperboy working again. I pulled R101 and checked it out of circuit. It is fine, along with the other "*" critical ceramic resistor near it. One thing I did see was that one of the leads of the white rectangle resister - R89 I think, was cold soldered. One lug of solder was completely detached from the solder pad. SURELY this was the problem! I fixed everything up, resoldered a few more questionable lugs, and put R101 back in. I put everything back together and popped her back in, confident I had FINALLY solved the problem.

Once again, nothing, zip, zilch, nada. DAMMIT!!!!!

I pulled the cardboard off the neckboard and checked B+. I didn't get any voltage at all on any pins of P202. According to the flowchart, that has to be shorted HOT or bad regulator. I JUST REPLACED BOTH OF THOSE IN THE REBUILD!! Is it possible Bob Roberts gave me a bad regulator? I don't have a desire to buy a new one if that isn't the problem.

Anyways, I am soooo tired of messing with this. I can only spend so much time without results before I'm ready to shit can things. Friz, I'm giving you a ring.
 
Somebody please give me some direction here. I am so burnt out on troubleshooting this chassis that I am looking for a replacement. Anybody want to take it in for a repair*? ;)



*I already have a pin board out for repair that I'm starting to wonder if I'll ever see again. If anyone seriously wanted to take a look at this, I would expect a quick turnaround.
 
shardian said:
shorted HOT or bad regulator
Click to expand...

the only thing i can think of is the mica insulator not right? try unscrewing it from the heat sink with a slight bend away from the heat sink and turn it on for a couple seconds to see if it comes up. if it does, then you know its working and was shorted.

might have to retest transistor in case it got fried because it was shorted...
 
I know both insulators are there and intact. I suppose I can at least check for shorts to the heat sink though.

Isn't there a diode I can pull from the circuit to test the Vreg? I've always been hesitant to do that test, because I'm not a fan of unregulated Xrays. ;)
 
shardian said:
I know both insulators are there and intact. I suppose I can at least check for shorts to the heat sink though.

Isn't there a diode I can pull from the circuit to test the Vreg? I've always been hesitant to do that test, because I'm not a fan of unregulated Xrays. ;)
Click to expand...

If the Xray circuit was the problem the monitor would power up for a split second then fail. Theres a large resistor in the right back corner of the board that fails, check that. Also, with the board installed in the game, check for DC voltage on both sides of that large resistor on the outside on the left side of the chassis.

Follow the path of the voltage. Make sure your fuse holder is passing 110VAC, make sure the rectifier circuit is passing 120VDC (could be 130). Its going to be something simple I just know it.

Is anything getting warm to the touch after the boards been powered on? DONT go poking around looking for heat with it powered up though.

Matt
 
The big problem with this board, is that it is pretty much INACCESSIBLE while installed. Do you guys have a magic secret for being able to do these in-game tests you mention?
 
Set up a TV tray or other table behind the game. Stick monitor on TV tray (or other table). Plug in and go.
 
if I still had the Paperboy here, I would. But I don't have any med-res games here at them moment..
 
You know, I just realized I have never checked C36. Doesn't really matter though, because it only fails to short - which would blow the fuse.

I have zero life at all, which pretty much rules out C36, and Vreg.
 
Okay, time for mo input.

I found another large resistor with a crappy joint. Apparently, resoldering just isn't good enough. I've taken to pressing slightly on suspect joints. I think this one was R96? It was behind the width coil. Anyways, the joint just snapped off, and the pad was gone. I soldered the leg down onto a chunk of exposed trace with good continuity. Surely now I'd get SOMETHING. Nope.
I kept testing for voltage. There is nothing anywhere on the board. No B+ at all on either side of that big resistor. So, I figure the flow chart has to be right - power just isn't getting in there...

The damn fuse was checking out fine as usual...but wait - I'm getting 25 ohms when I test the fuse. I pull the fuse (I have done this before mind you during this ridiculous adventure ad it tested fine) and it is no good. It LOOKS perfectly good, but it isn't. 100% open when out of the holder. I dig in my old K7000 parts (always keep your old parts when you rebuild a monitor kiddies, most of them are still good) and grabbed another fuse. Tested it and popped it in. Still nothing! But wait, I hear a light pop/snap here and there, but it isn't coming from the tube...weird. I test the B+ at the large side resistor. Around 156 on one side, 1.5 on the other. So I am in shutdown. Then, the large resistor starts smoking.... crap

I shut down, and notice that resistor had a corner barely touching the black crap on the tube. Easy to happen when you have to take off a whole side panel of the supporting frame to test....

I pulled it away, and fired it back up...nervously. Nothing again, and still the same meter readings. I for once had sense enough not to touch the resistor, but I put my finger close to it - alotta heat pouring off!

So guru's, what in the world is going on now?!? Why would that big resistor go into meltdown mode?

For the record, HOT tested good, Mica insulators are fine on HOT and VREG (no continuity between case and frame). VREG is proper number.
 
So the large resistor on the side of the chassis is getting hot, right? I'd pull the regulator out and see if its shorted. Also, make sure that all the CowPacitors (the large caps like C36) are not shorted. If any of them are they can fry the HOT and VR in an instant.

I'd be willing to bet that the side of the resistor that your only getting 1.5volts on is the load side. In order to pull that down that far you have to have something with some "beef" to it shorted. Could also be the HOT but you said you tested that. Could be the Flyback too...

Matt
 
shardian said:
Okay, time for mo input.
...
Then, the large resistor starts smoking.... crap

I shut down, and notice that resistor had a corner barely touching the black crap on the tube. Easy to happen when you have to take off a whole side panel of the supporting frame to test....
.
Click to expand...

Was a LEAD of the resistor touching the 'black crap' (aquadag)? It was effectively shorted to ground then. If just part of the ceramic case was touching, I don't think there's any electrical conductivity there.

If the lead was touching, see what in the circuit may have been affected by that being shorted. If some of these power resistors have too much current going through them or exceed their wattage, they could be shot. It could even test with a decent resistance, but open under load.

Did you find the transistor to pull to keep it from going to shutdown?
 
I talked to a local 'old timer' tv repair guy on the phone today. Explained to him my problem, and he went through the usual checklist of what is wrong. Obviously the problem lies in between the Ac line and the Vreg. I agree with that. He thinks C55, the filter cap is most likely shorted. He's seen the filter cap go bad on more than a few TV chassis in his day I assume.

Anyways, I never even bother giving that big black cap more than a casual glance, since everyone is always telling me it never fails. If my weak schematic reading skillz are correct though, it could definitely pull down the voltage, and is tied onto that big ass smoking resistor on the side - which I am pretty sure is R102.

Anways, I'll pull this piece of shit out one more time tonight. If this cap is shorted, and it is my problem, I'll be buying Mr. Old timer lunch.
 
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