Main Restorations Software Audio/Jukebox/MP3 Everything Else Buy/Sell/Trade
Project Announcements Monitor/Video GroovyMAME Merit/JVL Touchscreen Meet Up Retail Vendors
Driving & Racing Woodworking Software Support Forums Consoles Project Arcade Reviews
Automated Projects Artwork Frontend Support Forums Pinball Forum Discussion Old Boards
Raspberry Pi & Dev Board controls.dat Linux Miscellaneous Arcade Wiki Discussion Old Archives
Lightguns Arcade1Up Try the site in https mode Site News

Unread posts | New Replies | Recent posts | Rules | Chatroom | Wiki | File Repository | RSS | Submit news

  

Author Topic: WG 27K7327 w/P612 & NTSC decoder.  (Read 1745 times)

0 Members and 1 Guest are viewing this topic.

Amra

  • Trade Count: (0)
  • Full Member
  • ***
  • Offline Offline
  • Posts: 232
  • Last login:August 31, 2023, 05:22:46 am
  • Save a tree, Eat a beaver!
WG 27K7327 w/P612 & NTSC decoder.
« on: April 18, 2021, 08:44:43 am »
Chassis Model: P538 (Schematic)

This unit was purchased from a warehouse where it's sat for years, so its quite dirty.  I am rebuilding the frame which has some rust, and the wooden base is swollen and damaged.  This monitor was set up for use with laser disk games.  I doubt it was a dragons lair; I expect it was maybe used with a game like Mad Dog McCree.  It has the P612 riser board.  I have no use for the NTSC decoding function of this monitor, and it seems the board labeled P612 has what looks like a second horizontal width coil.  It has two connectors that go to the NTSC decoder board, so perhaps it has something to do with the NTSC functionality?

My questions are:
What is the function of the P612 board?
More importantly, can I remove this without issue?  Will I be able to use the board as a normal arcade monitor chassis, or do I need to do some further modifications to undo the added ntsc functionality?  There are some bodge wires that seem related to this purpose going to the connector for the P612 board on the chassis (pictured), and there is a secondary connector/harness soldered to R67 and R83 that goes to a connector on the P612 board. It appears to tap into some part of the deflection circuitry.

There is also a secondary board that appears to be connected to the flyback, a P741, which is also not listed on the schematic.  Does anyone know the function of this board?

Beyond this, so far I have not seen anything visually that is damaged save a broken contrast trimmer pot (pictured). 

I am comfortable with electronics, but have limited experience in analog circuitry.  I have ordered a cap kit, given it was sitting in a non-environmentally controlled warehouse for who knows how long, but I am curious what people think about replacing any other parts as a matter of course? I think I should not replace the HOT or Flyback unless they have failed, but do intend to purchase some as potential repairs at a later date, but there may be some other components that should be replaced that I am unaware of.  They say an ounce of prevention is worth a pound of cure, so if there is something I should just replace, or some maintenance that should be performed, I would be grateful for the advice.

I plan to do a repair log and share when finished, and thanks for any assistance anyone can provide.
« Last Edit: April 30, 2021, 08:33:35 pm by Amra »
Save a Tree, Eat a Beaver!

Amra

  • Trade Count: (0)
  • Full Member
  • ***
  • Offline Offline
  • Posts: 232
  • Last login:August 31, 2023, 05:22:46 am
  • Save a tree, Eat a beaver!
Re: WG 27K7327 w/P612 & NTSC decoder. Couple Questions.
« Reply #1 on: April 30, 2021, 07:23:52 pm »
Update; after closer examination the flyback had some hairline cracks in several spots, the HOT was shorted, and R103 was open intermittently.  I've ordered those parts from Peter and should have them soon.  Hopefully these take care of the issues, I haven't found anything else broken. I even checked all the width caps with an esr meter out of circuit, so hopefully we don't have any additional bad components.

As to the questions I asked earlier, after considerable research I have a couple answers so figured I would share what I found, in case anyone else ever has the same questions in the future.

The P612 board is a pincushion board.  The regular P538 chassis is primarily designed for a 25" tube. With some slight modification (typically a new width cap) It can be adjusted to mostly fit on a 27", but stretching the image so far will cause geometry issues (e.g. pincushion).  The P612 board is designed to correct the geometry when the p538 chassis is used with 27" tubes.  Apparently if you have a 27" K7000 this board will probably be present, and apparently these 27" K7000s are quite uncommon, so the documentation about them is pretty sparse. Regardless, it is needed.  So that answers that!  ;D

I will document all the modifications that have been made to this board, so that I have a written record in case any changes are made, so that I can revert it back to how it was set up originally (this assumes it worked properly with the current modifications, but that seems a reasonable assumption).

I haven't found any information on the P741 board yet. It seems to replace a resistor on the neckboard, but I'm not entirely sure how it functions. I will make a schematic to get a better idea, it seems at first glance like it uses some kind of inductive feedback from the flyback to control the current flow through a transistor.

Once the parts are in I will do the repairs, post the results and go from there! :)
Save a Tree, Eat a Beaver!