Centipede restoration - My first - There will be plenty of pics

Arcade Collecting > Restorations & repair

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pbj:
I mean, when you’re tooling around town buying free/$10 TVs, I think you just take what you get and put it in your neighbor’s trash can if it’s not suitable....

bperkins01:
Overall this cabinet is in decent shape, but its not without its issues.

The rear access door, rear panel for the power switch / powercord and the front coin panel were not in good shape. They had been wet for some period of time. The sides and side art at the bottom have expanded too - Not 100% sure of how I'm going to approach them at this time. But I'm experimenting. Replacing the original side art is not an option for me. The vast majority of it is very nice and I want to preserve it.

The coin door panel has screws connected to battens on the sides and staples across the bottom. It all popped apart pretty easily. Remove the screws and hit it a few times with a mallet. Out it came. The side battens were stapled in place and popped off. Same for the power panel / kick plate across the bottom rear.

At one point there *should* have been some 1/4" ply across the rotten part on the rear panel to secure the lower part. I can see where it was anyway.. It also appears there was a cover across the slot? I'm guessing to keep stuff from poking inside the cabinet. I'll figure out what it looked like and restore it.

Here is the lower power/kick plate. I'm certain this SHOULD be 3/4" - this is a full 1 1/8" thick. The black areas on the top and bottom are where it expanded - I knew particle board sucked with water - but I've never seen it show it so clearly.

The measurements came off the existing part pretty easily. It's 5" wide, 3/4" thick and 23 3/4" long. The angled part points downward. It appeared to be a 45 deg angle - but I put a gauge on it - and it was a 41 deg angle.. So I reproduced it at 41 deg.

Now I just duplicate the original. Screw the old part to the new one and cut the power cord slot and power switch hole. The little blocking I will move to the replacement. My machine has the original plastic plate that slides into these blocks to retain the power cord. One more bit of info I get is how much overlap I need on the 1/4" plywood on the rear panel/door. Obviously just enough not to hit these blocks.

Ready for paint and transfer of the power plate blocking.

One thing I can say about particle board - it hasn't changed in 40 years. The original material was exactly 3/4" thick - the new stuff - exactly 3/4" thick. I wish plywood was as consistent.

The original back panel was all blown up at the bottom. I cut the replacement to the exact size. Above I cut the slot part of the panel off and screwed it to the new back just to make it easier to work with. I like using the tablesaw fence as an alignment point so that I only need to get things lined up in one direction (east/west). Screw them together with a couple drywall screws and.....

Cut the new slot on the router with a pattern matching bit. You can't see it in the picture - but there was a bit of a wiggle in the cut from the factory original right where the straight part of the opening meets the rounded end - its perfectly replicated. I'll have to look at another centipede to see if this is in all of them - just because I can.

While I was at it - I recessed and drilled the opening for the rear door cam lock. The original is destroyed. But they are easy to come by..

Last major part I was unhappy with was the coin door panel. They used glue where they screwed it to the battens - but it popped right off. I can replace it to look original. Same steps - square it up to the fence and screw the old to the new. This is very doable even without a table saw. You could cut a replacement panel a little oversized and use the router to copy it exactly around the outer perimeter.

The original panel had 1/2" rounded out corners on the inside - so I used a 1/2" pattern bit. I precut the opening with a jigsaw to reduce the workload on the router bit. Here I don't have a problem using "ok" quality bits.. The wood and glue in particle board will chew them up.. No need to ruin expensive bits on this stuff.

After routing the inside - I used the original holes as drill guides to copy them to the new panel. Use backer boards on the far side to prevent blowout.

New panel ready for lamination.

Mike A:
:cheers:

yotsuya:
That’s a good looking back door. I just threw a piece of 3/4 MDF back there and it’s been good ever since .

bperkins01:
Back to fixing the CRT

I took a break from messing the the K4600 to build an Bench isolation power supply
It will make working on this and any future CRT's much easier to set up/tear down.

My teeny speck of a capacitor arrived - it came very well packed in this box. Not sure what is worse - that the box is stupid big or that a human taped it inside, filled it will air pillows and sent it on its way..

I put in on the main PCB (C627) - it made no difference to the horizontal centering circuit.

Now to try something that I do not think has been done this way before. The K4600 had many revisions and model numbers. Each with different schematics, components, interface cards, etc. The later releases of the PCB supported the P317 interface card which had a horizontal centering pot. I found a few references on KLOV that detailed the "Horizontal Centering Mod" for the K4600. It took a couple hours to decipher a few threads and consolidate all of the information. I'll assume if you got this far - you have recapped your boards and have the schematics. The centering mod is for K4600's where you cannot get the screen to move far enough left or right (obviously).

Basically here is the Horizontal Centering Mod summarized from other threads:

On your main PCB: (mine is a K4606 just for reference)

* Replace resistor R635 with a 6.8K 1/2W resistor
* Remove jumper J19 and put a 6.8K 1/2W resistor in its place
* If you HAVE a P317 Interface card
* Add a jumper wire on the back side of the board from pin 7 of the XY board connector to pin 1 of the Interface board connector (P302 pin 7 --> P201 pin 1)
This connects one side of R635 to P201 - you can see it if you follow the trace.
* Add a jumper wire from the opposite side of R635 to pin 2 of the interface board connector. (R635 --> P201 pin 2)
* The horizontal centering pot on the P317 interface card should now work with your older main PCB.After printing out both the P306 and P317 interface card schematics - it quickly became clear that the 'Horizontal Centering Pot' had no interaction with the actual P317 board. It just happens to be on it (I'm guessing because it was easier to do a mod on the much smaller board than the main PCB when they were being manufactured)

If you DO NOT HAVE a P317 interface board - give this a try.

Here is a schematic snippet (hopefully this is OK) - Copied from KLOV.

On the edge of my PCB there are many unused holes - I took a small 10K pot, bent a single leg down and soldered it to the ground trace on the perimeter of the PCB. Not perfect - but it holds it in place on the single leg.

Steps for mod:

* Solder one leg of the pot through an unused hole into the ground trace on the main PCB.
* On the center wiper pin - solder a 680pF Z5F (C204) capacitor.
* Add a jumper wire on the back side of the board from pin 7 of the XY board connector to the second bottom leg of the pot opposite the ground leg.
This connects one side of R635 to this leg. (P302 pin 7 --> pot leg not soldered through the board)
* Add a jumper wire from the opposite side of R635 on the back of the PCB to the capacitor on the wiper on the pot.
* This bypasses needing a P317 card completely and gives you the ability to center horizontally.
The furthest right I could get this screen before was this: (not sure how the get an iPhone to scan at a different rate than the screen - the bottom is not dim as shown)

With the centering mod:

This CRT still has a way to go. For starters I've been hunting for a few weeks for a donor TV - no joy yet. I'll experiment with convergence/purity on this one to get a feel for it. I have plenty of distortion and the tube is badly burned in. I'm not certain if the distortion is 100% a tuning issue or is having a crappy tube contributing to the distortion problem.

Two other things happened as a result of the mod:

* L351 - the Horizontal Oscillator adjustment (seems) to have become way more responsive. Before the mod it either held sync or didn't. Now it helped with centering and gave me some 'range' to work with.
* The Horizontal size coil (L702) also started doing more - I was able to make better adjustments. Previously I could get the screen to move maybe 1/4 inch.I could not have tried any of this without all of the information available on KLOV and the work done by others. Hopefully someone will find this useful.

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