Continuing to make good progress on this project. Here's what I've done since my last update...
Replaced Power Cord
The original Williams power cord was in rough shape (i.e., badly frayed & missing the ground plug), so I replaced it with the Home Depot extension cord
used by other KLOV members in the past (SKU #737774):
https://www.homedepot.com/p/HDX-15-...Tap-Extension-Cord-Brown-HD-737-774/100672778
Once you cut off the banana tap, it's a near-perfect match for the original. Here's a set of before & after photos:
The entire transformer assembly cleaned up nicely, too:
Rebuilt Power Supply Board
Next, I started working on the power supply board. I installed the D-8784 rebuild kit and cap kit from
@security0001 at arcadepartsandrepair.com plus a few other new parts: the +5V trim pot mod, a heat sink for BR1, and new SCRs (the legs on the old ones felt flimsy and about to break). Everything went in nicely, but here are a few things I noted in the process:
- R10 had been previously removed, which is recommended by the schematics if your +5VDC voltage is low.
- F2 & F3 were wrong, with 3A 125V & 15A 32V fuses installed instead of 5A & 4A.
- The following old caps were visibly bulging: C2, C5, C11, C13, C15, and C16 (which also had a cold solder joint).
- C14 had a really bad cold solder joint on the negative lead, as seen here:
Once I was done, I reinstalled the transformer assembly, power supply board, and heat sink back into the cabinet. I turned on the power with everything else disconnected because I wanted to quickly test the voltages being produced by the rebuilt power supply. To my dismay, LED #2 didn't light up on the power supply board, indicating I wasn't getting 12V. Before rebuilding this, I was getting all three LEDs to light up, so I knew I had made a mistake. I confirmed with my DMM that 12V was missing, so I started troubleshooting. Eventually I realized that I didn't have continuity between F3 and BR2, which surprised me since I always meticulously double-check my solder joints by testing for continuity — thanks, OCD! I remembered this joint in particular as being a pain to test since the trace connecting BR2 to F3 is on the parts side, so I had to have my DMM leads on opposite sides of the board. Taking a closer look now, the pad on the solder side was lifted, and new solder hadn't flowed through the via to the parts side pad connected to the trace. I'm guessing this was damaged when I removed the old BR2. The legs were a very tight fit in the through holes, so I had to snip them off individually and it was still tricky to remove them. Installing the new BR2 was very snug as well, and it was even trickier to now get solder to flow to the top side pad without removing the part. After a few magical incantations (i.e., lots of shouting & cussing), however, I finally got a good solder joint, continuity tested ok, so I fired it up, and my 12V was back... phew!
Sprayed Triple Thick on Bezel
I also wanted to address the severely flaking paint on the back of the bezel. I figured I would spray it with triple thick to keep it from getting any worse, and maybe touch up the paint by hand if I really couldn't stand it. Generally speaking, I prefer an imperfect original piece over a perfect reproduction, so I'm hoping I can make this work.
Here's an up-close look at some of the flaking (it's all over, but most severe with the red & blue paint):
I carefully masked off the viewing area and instruction card. As I was about to spray on the triple thick, I reread the directions on the can and noticed it said "Do not use in high humidity... If extremely humid, do not spray." So I checked the weather, and it said it was very humid... and would be for several more days. I also googled how long you could leave painters tape on a surface, and saw recommendations against leaving it on for more than a day or so. Yay. I then peeled off all the masking, waiting a few days until the humidity dropped back down to normal, and then carefully masked off everything again.
Per the instructions, I applied a "FULL WET COAT," and then a second coat about 2 minutes later. As it dried, I became a little concerned because about half of it was looking cloudy. So, again per the directions on the can, I reapplied "after 30 minutes to restore gloss." That didn't seem to help at first, but by the next morning, everything was looking nice and clear.
Recapped Monitor Chassis
I also used Peter's cap kit to recap my K4900, and while I had the chassis out, I replaced the bottle cap transistors, B+ filter cap, and the axial fuse, too. Here are some notes from this step:
- The vertical output section looked like it had seen some heat.
- I accidentally cut J45 while removing the glue holding C311, C507, and C701 in place, so I replaced it with the excess lead trimmed off of a new cap.
- C366 had a partially lifted pad.
- R503 had partially melted the insulation of the blue wire connecting point 51 to the other white resistor mounted on the frame.
- Both bottle cap transistors were very rusty.
- The B+ filter cap had a partially burnt pad.
I couldn't tell if this chassis had been worked on before, but either these jumpers, etc. were factory mods or old operator repairs (I left them alone):
Another thing I noticed was that two of the old caps had values that didn't match the new ones in Peter's kit. C308 was 3.3uF and 313 was 47uF, while the replacements were 2.2uF and 100uF respectively. There was a note about C308 in the cap kit instructions, indicating that a rare version of the K4900 chassis needed a different value for this cap if installing the replacement from the kit resulted in a fold-over issue. I did a bit more research and learned that this was indeed an early -023 version of the K4900 chassis. This had been discussed a few times before (see links to forum threads below), so I went ahead and ordered some additional new caps with values that matched what the -023 chassis needs.
I then centered all the pots, reinstalled the chassis in the monitor frame, and connected everything back together. I was feeling lucky, so I turned on the machine with the game boards disconnected to see if I could at least get the monitor to come up. I was happily greeted with some HV buzz and neck glow, and once I turned up the screen pot on the flyback just a smidge, got some good raster on the tube:
It was getting late, so I didn't bother balancing out the color pots at this point, but I did think it was kinda cool that the recapped monitor first came up with a hue of blue that matched the marquee.
Next up this weekend, I'm planning to cap kit the sound board, and then replace all of the remaining IDCs with new trifurcon pins and headers. At that point, I should be ready to fire up the game to test it out for the first time.
