Re: Amplifone monitor - still stumped on bright dot in middle.

Assuming there is not a CRT problem, I still think that the problem is related to a component that is common to all 3 color Z drives.
I took a look at the Amplifone schematic this morning to see what else I could find.
Refer to the attached marked-up schematic and PCB photo for component locations.
Mark-ups are in red and blue.
Here are a couple of things that you can check...

1) Check for 12V at the cathode of CR20. If this zener is shorted, the color drive will be extremely weak or non-existant. An open (or partially open) R71 can also cause the same issue.

2) Check the cathode of CR19 for 4.3V. If this zener is shorted (or leaking a lot), the Z drives will be weak or cut off.

3) Just because the spot killer (SK) LED is off doesn't mean that the SK output transistor (Q26) is okay. You can check Q26 to be sure that it is really off (maybe by seeing 4.3V is present) or just replace it to be 100% sure.

Just to clarify, when you stated "W jumpers are all long gone.", we assume that you meant that the old "0 ohm resistors" were replaced with solid wires.

William Boucher
http://www.biltronix.com
  ----- Original Message -----
  From: John Huie
  To: vectorlist@vectorlist.org
  Sent: Saturday, July 23, 2011 8:05 PM
  Subject: VECTOR: Amplifone monitor - still stumped on bright dot in middle.

        Just to refresh...this monitor on this Star Wars works good and the graphics are all there and everything but there's a constant bright dot in the middle. If I turn the brightness down enough for the dot to go away then I can't see the other graphics at all.

        Here's what I've tried so far:

        - Bought a whole slew of components from Bob Roberts to rebuild the deflection board and HV board
        - HV is good.
        - B+ is good.
        - Adjusting color drives doesn't help. Brightness down and the color drives up still won't let me turn down dot enough to see graphics well.
        - I don't have any spare parts to swap in. I only have 6100 vectors other than this.
        - double checked continuity from focus block wiring, all connections under boots are good. Good continuity back to HV board and color drives on deflection board are good.
        - Pins on neck not shorted to heater pins. (Except pin 4 which isn't used - could this be a problem?)
        - W jumpers are all long gone.
        - Resistors in neck board/ring are good.
        - Does same thing with known working PCB set.
        - Reflowed J103 and tested continuity along wires.
        - Ground to neck board/ring is good.

        Still not sure how to check Z signal. What components should I be looking at that are common to all 3 colors that could be causing this?

        Any other idea?

        Thanks everyone. I'm working on this for a friend of mine and just about at the end of my rope.

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Received on Tue Aug 2 11:59:38 2011