ugh... capped my k7000, now no HV

[ChadTower]

So, recapped the monitor... now no neck glow.  Checked all the caps, one was in backwards, so I turned it around and no change.  Maybe I fried that one cap, I'll swap that out and see.

What I'd like to do is test the B+ but I'm not sure on exactly where to take the measurement.  This is from the manual's flowchart...



I understand taking B+ at pin4 IC4 but what do I use as reference?  Is that saying to use p202 pin3 as the reference?  Or is there a ground spot someplace I should be using?

[qrz]

it means B+ should be at either location referenced to ground.

would be helpful to know which cap was reversed 

qrz

[ChadTower]

C46 470uF was reversed... looks fine but I know that may not mean anything.  I can pull an image from the schematic for you if it helps.

Thanks for answering my question on reference.  I guess my confusion now is that I don't know where to take the ground reading on this board.  I'm still developing my schematic reading skills and I'm not finding the right ground for that circuit.

[MonMotha]

Backwards cap will often be (mostly) destroyed even if it appears physically fine.  Probably best to just swap it for another unless you can prove it good.

For a ground test point, the metal frame is an easy option.  Some boards will have a defined ground testpoint on the board.

[ChadTower]

Cool, frame is easy enough.  I wasn't sure if this thing had multiple grounds.  I'll swap out the cap tonight and see if that does it.

[ChadTower]

Pin3 of p202 on the neckboard shows 164v... too high, yes?  The flowchart would indicate that I now check IC4 to see if the value is good there... problem with that is I can't get at IC4 while the monitor is running.  Too far into the back.   

So if you follow the flowchart past where IC4 checks okay a couple branches indicate C36 as a potential culprit... I didn't touch that one so maybe it's just a cracked joint there.

One other thing that happened is while cutting out caps I accidentally cut out an np cap (C4).  I didn't have a replacement part, and it cut the legs pretty short, so I soldered on new legs and soldered it in.  It actually looks pretty good and doesn't meter a short but I'm going to have to replace that cap just to be sure.  I'm betting Radio Shack doesn't carry np caps and I'm going to have to order this sucker.   


EDIT:  wow, Radio Shack does carry it, at least on the website... in axial but it's better than nothing.

[Kevin Mullins]

Pin3 of p202 on the neckboard shows 164v... too high, yes? 

A little high yes.... I had similar off readings the last time I worked on a K7000 not too long ago. I'll rack my brain a second and try to remember what it was I was doing wrong.
Seems like it was something to do with meter lead placement or reversing the leads or something odd and then I got a spot on correct reading. I remember now, the battery in my meter was low, so it threw all my voltage readings off by about how much you are looking at.

The flowchart would indicate that I now check IC4 to see if the value is good there... problem with that is I can't get at IC4 while the monitor is running.  Too far into the back.   

Oh, but it can be done. The trick is to close your eyes while reaching up under the neck and weaving through the jumbled mess in order to reach it.
 
Seriously..... you can take the same reading from one end of the large 3W resistor mounted to the frame just on the other side of the voltage regulator. (IC4)
One end of the resistor should read like 145VDC and the other side (B+) will be around 130VDC.
 

So if you follow the flowchart past where IC4 checks okay a couple branches indicate C36 as a potential culprit... I didn't touch that one so maybe it's just a cracked joint there.

C36 is what they call the "critical cap" if I recall correctly.
Never had to change one yet, but have heard it can cause shutdown.

One other thing that happened is while cutting out caps I accidentally cut out an np cap (C4).  I didn't have a replacement part, and it cut the legs pretty short, so I soldered on new legs and soldered it in.  It actually looks pretty good and doesn't meter a short but I'm going to have to replace that cap just to be sure.

Sounds like your repair should be fine for now.

EDIT:  wow, Radio Shack does carry it, at least on the website... in axial but it's better than nothing.

Online maybe.... actually in a store...... good luck.

[ChadTower]

Cracked solder joint!  While trying to reach in to get the readings on that resistor (it's a fight fit to get in) I was pulling a little bit on the shield behind the flyback and the monitor popped on.  It's working right now, I can see the game.     So now to pull the chassis and start reflowing everything.

Of course, it's still too wide, and the ripple in the top inch of the image is still there, even after the cap job.  I was hoping at least one of those two issues was going to be resolved by doing this.  It's like everything in the top inch of the image is in italics.

EDIT:  BTW, thanks guys, the advice has been great and your assistance is highly appreciated.

[SirPeale]

Try adjusting the 50/60Hz pot.

[Kevin Mullins]

Try adjusting the 50/60Hz pot.

Ditto..... was just going to say that. 



Oh, and I've seen some do that top ripple thing when the contrast/brightness is adjusted too high. So you may want to also set those about midpoint, adjust the SCREEN voltage and then adjust the brightness/contrast to suite and see what it looks like.

[ChadTower]

I couldn't see where the 50/60 pot was so I pulled the chassis to find it and now I see it's right by the adjustment pots where I could get at it easily. 

Gotta do the reflow work anyway so at least it wasn't a waste of time.

[Kevin Mullins]

Hehe... yeah, guess we should have mentioned that it was a little oddball round pot and is kinda hiding right behind a regular pot.

[ChadTower]

Must have hit whatever solder joint was cracked as it fires up normally now.

The pot was already all the way clockwise... turning it counterclockwise made the curling worse.  Can't go any further clockwise to make it better. 

[SirPeale]

Reduce the height.

[Kevin Mullins]

Peale is all over it. 

I generally try to reduce both the height and width, adjust everything else like horizontal and vertical centering etc and then stretch those back as full as it will allow to fill the screen.

I have usually found just the opposite of what you are describing though...... usually damn near all the way counterclockwise works out better on that 50/60Hz pot. Another reason to shrink the image first, you'll really be able to tell if it's still curling.
But then again, each one can be a bit different I guess.

[ken_cinder]

I have a similar problem on the K7000 in my TMNT after a cap kit. Was there before, but you don't notice when there are other minor annoyances.

Adjusting the 50/60 pot doesn't get rid of it, the only way to get rid of it is to shrink vertical size to the point where there is over an inch of black screen area showing at top and bottom.

Could it be the filter cap that wasn't replaced or in the kit? I have one on the way anyway, but if that's defo not the problem.......WTH is?

[ChadTower]

I'll give that a shot... but that curled part of the image is larger than the pic makes it appear.  It's nearly a ful inch of screen real estate.  I'm going to have to give Bob Roberts' width cap kit a shot too.  I do have it on hand and there is no way on this one to adjust the width.  The left side of the maze is totally off the screen.

[ken_cinder]

There's no need for a width cap kit on the K7000 (At least on my P538 chassis, I don't know about the P447), just adjust the width coil on the chassis.

[Kevin Mullins]

Yeah, the width cap kit is only if the coil still doesn't adjust enough.

And use the proper plastic hex tool to adjust the width coil. 

[ChadTower]

The width coil is melted into place and cannot be turned.   

[Kevin Mullins]

Ouch..... it isn't running hot is it?

[ChadTower]

Barely warm to the touch after ~5mins running.  It looks like someone used a metal tool to adjust it and it melted just enough that I can't turn it with the plastic tool.  The tool twists - not enough torque and I suspect anything stronger would just snap the core.

I was going to replace the coil but was told that it only gives you like a quarter inch screen adjustment anyway.  Is that mistaken?  I have probably a full inch+ too much width.  The right maze walls are half off the screen and the left is an inch beyond.

[Kevin Mullins]

There is a little wire jumper, yellow wire I believe, towards the back near the IC4 and width coil that could be moved from one pin to another......
I just can't remember off the top of my head if that was for vertical or horizontal.

[ChadTower]

It's horizontal... looking at the circuit it changes path a bit and shifts the image right or left.  I tried that at first and it seemed to do very little if anything.  Definitely doesn't help if the image is too wide no matter where it sits, it only tweaks centering a tiny bit.

[ChadTower]

So here is an interesting one... I decreased vertical size as suggested and the curled image follows it.  It isn't the top inch of the monitor, it's the top inch of the game image.  When I scaled vertical size down all the way the top inch of the game image was still curled, well off the top inch of the screen.

So it has to be the signal and not the monitor.

[SirPeale]

Possibly some kind of sync issue.  Try adjusting the sync.

[ChadTower]

I'm guessing that one isn't a pot.  I'll poke through TFM and see what options I have for that.

[Kevin Mullins]

That would be the 50/60Hz pot......... while you have the image shrunk, try adjusting that again and see if there is any change.

[SirPeale]

I was talking about HSYNC and/or VSYNC.

[ChadTower]

I was talking about HSYNC and/or VSYNC.

Yeah... looked through the manual for both the monitor and the Berzerk... don't see any way to do this on either end other than that 50-60 pot.

[SirPeale]

On a K7000 it's H HOLD and V HOLD.

[ChadTower]

Peale wins!  H hold did the trick.  Thanks!

Just in case anyone out there has a similar disconnect in their brain... HOLD=SYNC=ROLLING SCREEN.  Somehow I knew rolling screen is sync and hold is rolling screen but not sync is hold.   

[Kevin Mullins]

I'm such a creature of habit when it comes to tweaking that sort of stuff I tend to over think the obvious like horizontal hold.
 

Glad you got it sorted.... and thanks to Peale for the pointers.