Dolly – rectifier board

So, those waiting along with me with baited breath for Dolly to come to life will have to wait a few more days.

I replaced the verified boards in the machine, and everything continued to work as it had previously.  I looked at the rectifier board – and tried to swap out the F1 fuse. No joy.

as-2518-18aI tested all the test points (TP1~TP5) on the board, and of course the first one is dead – and it of course links directly to feature controlled lights – which is the problem.

Now I’m faced with removing the board – which is itself soldered directly to the power supply. What a stupid decision – why didn’t they just add one more connector?  Well, they did on later machines. But not this one.

Looking at the image there is one big black square, and three smaller squares with circles within them.  One of these small squares is the bridge rectifier that is dead.

I’m thinking I’ll have to do one of 3 things

  1. Remove the board, and replace the three small  bridge rectifiers. The problem is they are undersized for the task and fail. So, I’ll need to use larger parts, and mount them to the front of the board, and re-solder the wired connections when done.
  2. Remove the board and steal a working one from my friend Kevin –
  3. Remove and replace the board with a solid state option for $65 bucks from someone like

Because I’m terribly frugal – it will most likely be option 1 or 2.  I do have some bridge rectifiers in a box of parts – so, I think I’ll most likely do option 1.  If I destroy the board then 2 or 3 ;).

Fingers crossed, but hopefully not the wires.



Dolly – she’s coming to life

The continuing saga of the Dolly Parton pinball machine…

I bought an Alltek MPU which arrived last week.  Immediately I swapped the old MPU out, and with fingers crossed I turned on the power… (baited breath inserted here)

The game scores, and plays – but the feature lights aren’t working… darn it! (something else inserted here).

After reaching out to GAPAS ( with requests for ideas, my friend Kenny came over to help with some testing. Unfortunately, we couldn’t quickly determine where the problem was. So, we took the boards (MPU and Lamp driver) over to his house and dropped them into his Six Million Dollar Man (painfully held breath) and  EVERYTHING worked!

This is great news!  I was afraid something was wrong with the Lamp driver board and I’d be having to purchase something new, or the new MPU itself was faulty.  But as they worked fine on his machines – I’m back to looking at the Dolly game itself.

Unfortunately, I left Wednesday for a vacation, and just returned home Sunday night [Well, not really unfortunately – it was a great time in Cancun].  I hope to have time tonight to put the boards back into the machine, and check the leads that Kenny sent me over the week and weekend.

I’m very excited to hopefully add Dolly back to the land of the living – she’s never been a good zombie and this half life living dead isn’t what I hope for her.

Mentally There… and my ongoing Arcade Repair

I’m now terribly happy I put together this blog.

After trying so hard with the Dolly MPU board and being so annoyed at the dramatic failure my efforts returned I found I was not in the mood to work on my machines for a few days.

Then I got distracted and a few days became a few months.  And this is where my happiness starts – I have an exact record of what I identified on each arcade game and pinball machine, and happily I don’t have to re-discover the issues on each one.  THIS is huge on projects with potentially so many pieces to manage.

And now that I’m about over my pride and annoyance at the failure with Dolly; I find myself ready to start thinking about doing more to bring things to life again.

So, HOPEFULLY in the next week or two after these next guests come through I’ll be ready to get back into the swing of things.


Find instructions for my arcade game Missile Command CPU board – or how-to troubleshoot it.  I’m thinking it is the power section that I should start with anyway and go through it logically.  It would be ohhhhh so much easier if I actually understood electronics somewhat…  😉 But I’m a dynamo at following instructions. If I could find a diagram that breaks down the sections of the board perhaps.  A picture with grouped items outlined – Power, Ram, Video, IO, etc – this would make it easier for me to discuss what I’m looking at on any given day.

A friend told me there was a ‘bullet proofing’ guide for ATARI games of this era (1979ish) regarding the power systems.  I wonder if that would provide me the guidance I need – any readers familiar with this?

Thanks those of you who have been patient and still are tracking at all what I’ve been trying to do.


Dolly – It’s Alive (again)!

Dolly Parton Backglass

Dolly Parton Backglass
The other day I was thinking about the 20k resistor that I didn’t have – and got to thinking.  “Can’t you run resistors in series or parallel to adjust the net value?” I thought to myself.  So, I called my dad as I thought that if you put them in series you then added the ohm rated resistance values together.

I have an 18k, and I have some 1k’s – I need a 20k…  So, I soldered the selected ends together (after calling my dad to verify) and put them in. Hoping against hope – I put the board in the machine and gave it power.

I had the machine  where the LED (which indicates boot status success/failure) to be constantly on. I counted this as progress.

Tonight though I had some more time

So, I re-verified all the continuity points for my U8 IC on the MPU.  And of course found a number that needed to be updated.

If you are a follower/reader you know that I recently determined there was more corrosion damage than I had originally thought (in my haste). So, I spent the past few times that I’ve had free to remove that, and install a socket for the U7 chip.

After this process the LED got through the flicker and first flash.  YAY – there needs to be 7 successful flashes for the game to boot up as each one indicates a phase completed.

Energized with my success I realized that I had not verified continuity on the U7 socket that I had replaced. And remembered belated that there was a trace that had evaporated in the corrosion cleaning phase under U7.  I found one leg of the IC completely isolated from the game – figured what points it needed to connect to.  Verified each of the other 21 legs on the chip – and after 2 hours of testing and soldering I decided to hold my breath and plug it in again.

Watching the LED like a hawk – it flickered.  Then flashed… once..  after a bit of a pause it flashed again, and again, and again, and again, and again, and again – and then there was a sound sequence, and the scores lit up.


The game is now in the same playable state as it was when I received it – but it not longer has the battery leaking more corrosive gasses and destroying the game.  It now really looks like  a Frankenstein machine with trace wires crisscrossing all across the back.  It isn’t pretty, but it is working – and I didn’t have to spend $200 to replace it.  I can live with not so pretty when no one will see it unless they pull the board out of the game.

Now.. time to run down the switch problems…  (next post)

Bally MPU Corosion – Woes and Repair continues

MPU Pre-Cleaning
MPU Pre-Cleaning

MPU prior to cleaning process

Well tonight – I finally got in the mental space to re-approach working on the MPU for the Dolly Parton pinball machine.  I was disheartened when I finished the installation of the U8 last week.

I had verified all the connections were correct – and replaced the capacitor just below the IC.  Everything then tested as I expected, so with great hope I put the board in the pin.  My hopes were dashed when I powered the game on. Nothing happened other than a bit of beeoooop noise once. I flipped the power a couple of times – not expecting anything different, but hoping.

Dejected I took the board out, and placed it on my card table work bench.

So, a week later (today) I got the gumption up to work on the board again.  I figured the reset section was not working correctly.  The green LED comes on, but doesn’t go through the flicker/flash boot sequence.  So somewhere something in that section must be out of whack.  This is not coincidentally the same section that is usually directly affected by corrosion.

Today – I cut out and de-soldered everything else in this area. Imagine my surprise when I went to remove one of the larger resistors in this section the lead popped right off.  Apparently there was more corrosion problems than I had assumed.

After sanding, scrubbing, cleaning I began to put in all the replacement parts that I had purchased last week for this section.  I spent about three hours on this process I had one spot left for a resistor. I was annoyed after going through my entire box of parts and rechecking the bands on every loose resistor that I have.

I need to purchase one 20k ohm resistor to finish this project. Annoyed as I had gone with a list to the great local supplystore (ACK Electronics), and thought I’d purchased everything needed… but it appears I missed one item.  I did get one resistor that didn’t match anything on my list – so it must be what’s wrong.

Guess I’ll be back to the store this week unless someone has one on hand they want to drop by. 😉

I had been hoping to see if this would bring the machine back to life – but it’ll be a bit longer until we find out.

Dolly – Bally MPU U8 progress

With the help of my friends at GAPAS I was able to determine test points and continuity areas of my Bally MPU for the Dolly Parton pin so that I’ll be able to put in jumpers where necessary to resolve the problems with U8.

However, while testing I found that pin 8 and pin 22 were showing continuity. I was pretty sure this shouldn’t be the case, but as I have only this Bally pinball machine – I have no other MPU to test against.

Today I was able to get my friend Robby to help me – as he has a few.  He verified that there should not be continuity between 8 and 22 as I suspected.  But then there is the issue with – well why are they connecting when they shouldn’t.

I knew that pin 8 was supposed to be connected to ground for the power portion of the circuit.  And it looked like 22 should have been to a positive power source – and after checking pin22 did seem to test good to the little through hole solder junction on the board (with a + sign next to it).  Of course this wasn’t foolproof as I was testing continuity between that + and ground… which is a big obvious NO NO.

After having stared at the board so long while determining the pin out connections – I was thinking perhaps it was a bad capacitor.  C13 seemed to stand out to me – it is near the battery, and could have been damaged some way from the acid problem.  Or, perhaps, it was due to heat or some other from when removing the IC stand at U8.

I cut a lead off the capacitor – and like magic no more continuity between + and -.  Now, I’ve added a new 0.0uF Axial Ceramic capacitor to my shopping list for this week at the electronics component store..

Hooray for progress, and thanks again Robby.

Bally MPU Corrossion – Woes and Repair

U8 image

U8 image

I’ve cleaned up the corrosion on my Dolly Parton MPU (Bally) – BUT Some of the traces were really damaged and a few I can’t determine where they should connect, and others might not have continuity any longer.The only component apparently affected that I have had to replace and am concerned about is the U8 chip.Unfortunately I can’t read a schematic well enough to figure out where on the board I should be checking.

I’ve been looking online for a quick guide of what to check and where each pin should connect on all the normally damaged components as this is a REALLY common problem with Bally’s, BUT I haven’t found anything that will really help. Basically a trace diagram for the MPU would be awesome but alas I’ve not turned one up.  And I’ve not found high enough resolution images of the front and back to work from reliably.So, does anyone know off the top of their head where all 22 pins on the U8 should have continuity to?  🙂  If I need to add jumper wires it would be awesome to know where they should land.

I’ve been trying to map this out and here is what I have so far.  I know some of the legs should have continuity with other legs on the same chip – but not 100% sure which those might be, and if the pair also should have continuity to some other component.My notation is IC / or resistor/capacitor #.  e.g. U7.1 = Chip U7 Pin 1

1 – U7.20
2 – U7.21
3 – U6.6
4 – U7.23
5 – U7.18
6 – U7.17
7 –
8 – GND
9 –
10 – U11.29 (??Paired with 9?)
11 – U11.28 (pair12)
12 – U11.28 (pair11)
13 –
14 – U11.68 (??Paired with 13?)
15 – U11.26 (pair 16)
16 – U11.26 (pair 15)
17 – U18.6
18 – U17.8
19 – U17.6/ U10.23
20 – U18.7
21 – U6.4
22 – R12 left leg (also Big pad which I believe leads to Batter + terminal)

Do Pins 11 and 12 only link to the other? Should there be a connection anywhere else? As you can see I’m missing a couple which I’ve not been able to identify.


One of the GAPAS members (Ken) sent me the following based on his review of the schematic:

1 – (A3) U7.20 / U6.5
2 – (A2) U7.21 / U6.6
3 – (A1) U7.22 / U6.7
4 – (A0) U7.23 / U6.8
5 – (A5) U7.18 / U6.3
6 – (A6) U7.17 / U6.2
7 – (A7) U6.1
8 – GND
9 – (DI 0) U11.29 / U7.6 (pair 10)
10 – (DO 0) U11.29 /U7.6 (pair 9)
11 – (DI 1) U11.28 /U7.7 (pair 12)
12 – (DO 1) U11.28 /U7.7 (pair 11)
13 – (DI 2) U11.27/ U7.8 (pair 14)
14 – (DO 2) U11.27/ U7.8 (pair 13)
15 – (DI 3) U11.26 /U7.9 (pair 16)
16 – (DO 3)U11.26 / U7.9 (pair 15)
17 – (CE 2) U10.34 / U11.34
18 – (OD) U18.6
19 – (CE 1) U17.8
20 – (R/W) U18.7 / U10.21 / U11.21
21 – (A4) U7.19 / U6.4
22 – (VCC) R12 left leg (also Big pad which I believe leads to Batter + terminal)
The (A)ddress lines and (D)ata lines will go to multiple chips.

QUESTION: should I be getting continuity between 8 (gnd) and 22 (VCC) ? If not then I’m wondering if I need to replace C13