Replacement Bally -35 MPU PCB's - Unpopulated!

[Homepin]

Hello all,

I have been asked to post this info in a new section so that it will be more easily seen by those who might be interested so sorry if I am boring those who have already seen it.

We (at Homepin) are recreating a Bally -35 MPU mainboard and it is our intention to offer it as an unpopulated, blank printed circuit board to pinball enthusiasts.

The concept being that you would be able to build up a BRAND NEW board using parts from a dead or battery damaged board or use new parts if you wish.

These machines are now 30 years old and the MPU boards are dropping like flies mostly due to leaking batteries.

Our new board is as close to the original as possible but with modern improvements such as a socket for reomote batteries - also provision for a supercap should you choose that option. We will also include jumpers so that more modern, and more easily available parts can be used to build up the board.

We will be supplying it with a few key parts such as strip connectors, 0.22uh chokes, socket for the external memory battery pack etc as these few parts will be specific to our board. Upgrade packs of various components will be available right through to a complete package with all parts required to build the board.

Notably we don't aim to supply it ready built - there are many others doing that such as the excellent multi purpose Altek board. Our goal is for the board to be as close to original as is possible whilst including some modern improvements - BUT mainly as a "build it yourself" style project.

Future projects include a blank MPU board for Zaccaria machines. I will write more on that as we progress with it (it has been started - but is still very early days with that project).

Here is a screen shot of the Bally board as it currently stands and we hope to have finished boards ready late January after we have built up a few to prove they are OK. Price wise we are targeting 'under' $40 and doing everything we can to keep it as low as possible. Naturally upgrade parts kits will add to this price.



and here is a closeup of the 'extra' bits area so a 6802 micro can be used with a Crystal if desired instead of the hard to find 6800:

[Strangeways]

I will be buying a few of these boards Mike !

I assume the board will be "almost" a "plug and play" - Replace U2 / U6 (2732) and you are ready to roll ? I like the idea of the board being original as possible.

[63wizz]

I like this idea as well, cant wait to have a go at building one of these boards.

Ian

[Strangeways]

Hey Mike of you need a tester - I'm happy to install one on my Paragon since I play it almost every day !

No discounts of course - just keen to provide feedback.

[Homepin]

Well we are in the final labelling and double checking stages of the Bally -35 MPU board. Another day or so and it should be ready for the circuit board house to make the first batch. Some might note we have 'beefed' up the tracks a little and we have used some artistic licence to make several small improvements over the originals. One of these mods can be seen in the last picture where we have retained the original (dumb?) mounting holes for the transistors on the board so that people who wish to assemble it as close to original as possible are able to - but we have added more modern (and sensible) pad layout for these transistors.

After that we will have to assemble and test a few to confirm all is OK. This will take another month and then the writing of the assembly manual probably a further month. Here are some current shots of the artwork (still with legends to mark and move about).

Bottom view


Top view


Closeup near the EPROMs


Sensible - added transistor mounting holes

[wonder]

Well done Mike i am sure you will move a few of these.

[Mr Pinbologist]

following this thread with great interest, as well as the Zac mpu thread

are there any plans to reproduce any other boards?? keep up the great work

[Homepin]

A small update. We have finished the layout of this board and the staff member who did most of the layout has 'handed it to me' for a seperate check (that way it's MY fault if there is a stuff-up, hahaha).

Here is a close up of the battery backup area showing what we have done here:




Those familiar with these boards will recognise the three large mounting holes for the backup battery. We have included these just as they are on the original board in case anyone is actually stupid enough to want to fit a backup ni-cad........ ....…let's face it, the battery leaking is probably the very reason you are building up this replacement board so I can't see many (any?) choosing that option.

Of more interest is the small socket marked "REMOTE BATT" for plugging in a remote battery pack and then to the right of that a small, 2 pin header marked "MEM SW". This takes a standard computer type shorting link and connects the supercap (to the right of the switch) to the 5101 RAM. The reason for the switch is so power can be removed from the RAM in case of repairs or RAM swaps.

So this board provides three backup options:

(1) Exactly as per the original board - ni-cad battery pack mounted on the PCB (stupid idea)
(2) Socket for a remote battery pack (much better idea)
(3) Provision for a Supercap (1F 5.5V) and a link to disconnect the cap when required (also a better idea than the original)

[Strangeways]

Suggestion - instead of having provision for Ni-Cad, how about an extra hole for a CR2032 battery socket and blocking diode ?

[Homepin]

I do like the idea and there is plenty of board space to incorporate a 2032 battery in addition to the other options. The only drawback is the 'standardisation' of a socket to suit such a battery - I will certainly look into it - thanks for the valid feedback.

[FirePower]

The flexibility with the battery provision is great - let people choose what they want.  The reset link for the super cap a good and necessary feature.

Minor gripe / observation is the connector for the remote battery pack and the lack of keying it for polarisation.  I know the board is screened to indicate polarity, but I'd like to see some fool proof way of getting it right way around. There are plenty of us fools out here.  Maybe the circuit provides reverse polarity protection?  I'm not familiar with it and if so  then all good.

In any case I reckon you are doing a great job.

[Homepin]

"connector for the remote battery pack and the lack of keying it for polarisation"

We really do appreciate ALL feedback, let's make the best board possible! Please keep the comments and suggestions coming.

It's all good - the socket (that we will provide with each blank PCB) is polarised - we have also added a diode on the board to prevent charging of dry cells used remotely - here is a picture of the socket we intend to provide:

[Homepin]

OK - a quick update on this project.

We have completed the PCB layout and are currently spending a huge number of hours checking every track to ensure the layout is accurate. I have been caught out having boards made previously so I am always very reluctant to have PCBs made without having the actual parts in stock to make them with - it saves nasty surprises later!

Here you can see the TACT switches that will replace the obsolete 'red' test switch on the board:

     



Also the CR2032 battery holders arrived and we have confirmed the position and correct location for them. We have incorporated a schottky (low forward voltage drop) blocking diode into the circuit and it can be fitted if the board constructor chooses either the off-board AA battery pack option or the on-board CR2032 option. There is also a two pin header with a shorting link that can be used as a memory battery disconnect when working on the board - especially around the RAM.

   

We have also added many more words to the board denoting what certain pins connect to etc (left pic). Also, after carefully reading some of the common problems as outlined on Clays Pin Repair pages we also improved several areas. The picture on the right shows how we have added the ground connection to both upper and lower board traces to improve the grounding of these pins and you can also see in that picture "C5" and "C5B" - 5B is to allow for modern single ended electrolytic caps to be used in place of the (hard to find these days) axial style caps:

     


We are pretty well on time with this project and at this stage expect finished boards to be available end of Feb or early March.

[ajlaird]

Looking good, should be a winner!

[chris288]

Great work

Really looking forward to these becoming available.