Surprisingly, marco has it. But it's almost 6 bucks.

http://www.marcospecialties.com/pinball-parts/5551-09822-00

Some googling just turned up modern SMD/SMT parts.

The choke is listed in my standards parts spreadsheet in this thread, it's $3.22.

Ok, I dug around on mouser a bit, and found a few possibilities.

I'm not familiar with inductors, so I'm not sure if it's ok to go with one rated for a higher amperage. here are 3.4a and 4a variants available.

http://www.mouser.com/Passive-Components/Inductors/Fixed-Inductors/_/N-wpcz?P=1z0wrgfZ1z0z819Z1z0jl4i

Whoops, forgot about that: https://pinside.com/pinball/forum/topic/partially-assembled-twobits-wpc-mpu?tu=pin_guy#post-3292953

I have the replacement choke picked out from the manufacturer but never had the time to pull the handle on this one.
Samples... absolutely the best way to get onesy-twosy parts. Molex is real good at this for connectors but limits contacts to only ten or so.

http://www.digikey.com/product-detail/en/epcos-tdk/B82144B2472K/495-6770-1-ND/5209437

Mac622 and Pin_guy:

Have either of you noticed that the RTC clock runs fast? Really fast...

My build was also fun and something everyone, who is looking to improve their soldering skills, should do. Anyway, the board started without a hitch, I set the clock, and played many games. I then noticed that 90 seconds would pass for every minute. Ugh...

I purchased a quality crystal/Xtal (Citizen, 32.768KHz w/ 12.5pF) and thought there might be lots of "noise" from the board. So I brought out the trusty oscilloscope. The trace at U9 pin 70 was pretty; no noise. So, I compared the clock/signal from the new "Two Bits" and the original WPC board. Sure enough, the Two Bits board runs fast. You can see in the pictures there's 1.5 waveforms to the original's singular/full waveform. There's no way my crystal could be that far off!!!

OK, referring to our trusty WPC schematic, R91 is 22MΩ and R92 is 470KΩ. Looking at the original board, you can clearly see a <b>Red-Red-Blue</b> (gold tolerance) banded resistor (22M&Omega, and a Yellow-Violet-Yellow (gold tolerance) banded resistor (470K&Omega

But, on my Two Bits board, R91 is <b>Red-Red-Green (2.2M&Omega</b> R92 is fine. Looking at the (amazing) initial photos from Pin_Guy, his photos match my board.

As for C28, C29, and C30, I can clearly see the color coded radial capacitors on the original board; they match the schematic (100pF, 22pF, and 22pF). The Two Bits board, I can see "220" on two <i>chicklet</i> capacitors, 22pF at C29 & C30. As for C28, I can only see "1 ( ) 1K". The "( )" is an odd encoding, but I'll interpret that to be 10 multiplied by 10, 100pF with "K" tolerance. Anyway, I'm pretty confident that the capacitors are right in the timing circuit, Only that R91 is wrong.

Thoughts...

A12742_rtcSignal_U9-pin70 (resized).jpg

twoBits_rtcSignal_U9-pin70 (resized).jpg

Are there different versions of the ULN2803 chips? Amazon shows ULN2803's, ULN2803A's, ULN2803APG's. What's the difference? Will any of them work? I have an intermittent on my TZ that I'm tracking down that keeps killing them. I'm looking to buy the cheapest possible ones.

thanks,
Steve

I don't see any issues with the clock frequency on my board.

Here are my clock signals at U9-70:
CH1 (yellow) is the TwoBits MPU running on my workbench
CH2 (blue) is an original Williams WPC-89 MPU installed in STTNG.

There was a very slight roll on channel 2 (non triggered) due to a minor mismatch in frequencies; I put the O'scope on STOP after letting channel 2 roll to the cursors.

32KHz Clock Signal (resized).png

Correcting the value of R91 should fix your problem.

I used my TwoBits board to recreate the substitution of having a 2.2M resistor instead of a 22M resistor at R91. First I captured the expected 32.768kHz clock frequency at U9-70 and saved this as a reference waveform R1 (green). I then placed a 2.44M resistance (R91B) in parallel with the 22M R91 resistor, this essentially dropped the R91 circuit resistance to 2.2M ohms as R91B = 22 x 2.2/22-2.2.

This change caused the average frequency of the clock on CH1 (Yellow) to nearly double its rate to 62.851kHz as seen below.

Bad Clocks (resized).png

Just had a look at the ebay link to these boards quoted above, was all ready to purchase as I thought this would be a good project and having a spare mpu board would be a good idea in case my TAF develops an issue, then I saw the shipping to AU $25.26, to quote a popular aussie film, 'Tell him he's dream'n'.
For those of you not familiar with the film..

Hey All,
I wanted to "close the case" of the "speedy real time clock". My board truly had an incorrect 2.2M ohm at R91. My clock now keeps time, but only after replacing R91 with a 22M ohm. From above, you see that Pin_Guy's board has an accurate clock, so maybe some boards have the right resistor and some don't. It may be cheaper to order one or two 1/4 Watt 22M ohm resistors while placing the full order. Then to find out afterwards, that you need one. Good Luck.

I don't think this was isolated to just your board, I've seen a couple other pictures of these boards which also appeared to have a 2.2M resistor installed as well; of course anyone using NVRAM wouldn't notice anyways since the clock is always going to be off unless they never turn off their machine.

I didn't actually start with a partially assembled board for this project, but opted to buy a completely blank board and and the parts, a link to the complete BOM is listed near the beginning of this topic.

Thought I would breathe some life into this thread. Just did a partially assembled board. I used components from a thrashed original WMS board. At first the game would come up crazy, was the NVRAM I was using. Put in original RAM and game fires up and plays. Having a few issues but think it's the ribbon cables.

Time does go double speed, so will be replacing R91 with a 22M.

I ordered some full blanks to try next.

Quick question, I noticed on my 'partially built' board, w6 is jumpered and w7 is not. This is the opposite of the factory wms board. My board is set for a 6264 FYI.

Does anyone know what w6 w7 does?

I noticed "Pin Guy" jumpered his just like the WMS board.

W6 / 7 selects power to RAM. (5.0 / Vcc)

W6 = memory loss on power shut off
W7 = memory remains

Ok so if my board is jumpered w6 on w7 off, and has a standard RAM installed, it will lose it's settings (even with batteries installed) and w6 off w7 on it would retain?

Yes, that's correct

Thank you so much for the info. I assume everyone that purchased the partially built boards will have an issue with settings being retained when using batteries and conventional RAM.

I am using NVRAM on mine I only asked the question to understand the difference.

Wonder why WMS had the option to not retain settings?

I moved the jumper on my board and now power is supplied properly from the battery pack FYI.

On another note, I swapped R91 with a 22M Ohm resistor and the board doesn't boot. Non of the LED's light and the 5v shuts down. I'm going to put the original resistor back in and see if it boots.

R91 is ONLY used to establish the RTC clock frequency.

Yeah I don't get it. I'm double checking everything.

Make sure you aren't shorting your 5V out with the mounting screws; the 5V bus on the topside of the boards runs way too close to these screws, I usually put nylon insulating washers on the top side.

I bet that's it. This was the first time I tightened the screws. I will report back.

That was it! Ran board not secured to backbox and it comes up fine. Thanks for the tip.