WMS System 6 CPU board repair

[Steevsee]

I bought this board off ebay and followed Clay's guide to repair it.  It was listed as having Firepower roms and needing work.
Powered up on the bench and both leds flashed once then locked on.  No displays/lights working.

The board had some previous work done, which was quite obvious due to the old flux which was encrusted all around it.  Also the game rom was a hacked piggyback setup which can be seen in the first pic. 

First step was to clean all the old, dry flux off the board on both sides.  Using isopro alcohol and an old toothbrush I started scrubbing.  Some parts were so thick that I had to scrape it first with a small screwdriver and then scrub with the toothbrush.  Also removed all socketed chips and cleaned the flux from around the sockets as well.

Once all the flux was removed, I put the board through the dishwasher.  Once the cycle was complete, I removed excess water with a compressor, then gave a good rinse with Isopro to all the switches, before thouroughly removing all remaining water with the compressor, particularly around sockets and connectors and under chips.  Then I gently heated the board for about 15 mins to ensure that it was totally dry before applying power.

The board is much cleaner now and far easier to follow traces, check continuity and troubleshoot in general.   It also just plain looks nicer.

Next up I will replace the old rom chip sockets.

[ddstoys]

Old flux can be a real bitch i like the dishwasher idea to clean the boards.

   Will you be able to use your test board for this repair?

[Steevsee]

Yes, the cpu tester was once again very useful.  I had to make up another heap of cables to connect it, but I should be right now for any future boards from WMS sys 3 - 11.

Following clays guide, I set about replacing the rom chip sockets on this board. 
I was able to easily remove the plastic casing on all but the machine pin socket.  It is certainly much easier to remove these socket pins one by one, than try to desolder the entire socket at once. 

I think the machine pin socket was probably ok, but I didn't really like the look of it so I ended up replacing it as well.  I used side cutters to carefully breakup the plastic around the pins before removing them one or two at a time.

After all the old metal legs were removed, I used a cheap soldapult and plenty of flux to clear the holes.  After this I cleaned all the flux off the board with isopro before checking all traces around the sockets and installing new machine pin strip sockets.

I wasn't too sure about the piggyback rom setup and to be honest I got quite confused while reading the roms section of Clay's guides and had to re-read this part about ten times!
Eventually I figured that I needed to move the jumper wire from J4 to J3, so that i could use a game rom at IC14 and not have to use the top three sockets. (IC26, IC22, and IC21)

I tried to boot the board using the supplied piggyback rom chips, but the cpu leds still just flash and lock on. 

Hmm. Could this also be a problem in the blanking circuit, just like my last repair?   

Unfortunately not. After getting all excited and replacing the capacitor and transistor in the blanking circuit, everything was still the same.

I did notice at some stage that if I pressed down on IC15 while powering on the cpu, that one of the leds would go out, which was at least some progress. Cut off the old chip with a dremel and socketed and replaced a new chip but this still didn't seem to make any difference. 

Time to concentrate on the roms as i really didn't know what was on the piggy back chips, so I pinched the roms from my Stellar Wars and tried them. 

CPU booted straight away, leds flashed and then went out as they are supposed to.  

Took the opportunity to print and apply some fresh stickers to my Stellar Wars chips as well.


More to come.

[Steevsee]

With the board now booting and running well, I replaced all the header pins and added a new remote battery connection. 

Still plan to replace the 40 pin inter-connect headers as well, but unfortunately my order for these parts was delayed.

I have now been running this board in my Stellar Wars for the last few days and it seems to be working fine.

Here is a before and after shot of the cpu board.

[Homepin]

Brilliant work - well done 

I find cleaning flux is better using Acetone as it doesn't leave a whitish residue like isopropyl or metho.

[ddstoys]

Acetone man I thought that stuff ate everything.   I'll have to give it a try I hate the white residue

[FirePower]

Good to see some circuit board lurve. I've got a few WMS boards to repair and so have been thinking about some of these issues, so hope you don't mind, but here are a few thoughts. Happy to hear others' opinions.

There are a couple of different methods floating about for modifying the address select for the roms and it looks like you might have a few of these in the first incarnation of the board.  That green link wire in your first post looks a bit dodgy.  Some methods also cut traces and stick a link and or diode on the reverse of the board but I can't see it on yours.

I find the whole rom / prom changing story confusing and Clay's guide whilst great and very generously provided would benefit from some quality editing to make them more readable and usable. So much info is repeated and placed in ad hoc locations.  

Another view of the same rom stuff is presented here http://pinball.flippers.info/  and I think Leon's site talks about it also.

To me it seems the best approach is to remove all the old bodges, put J3 in, J4 out and use a 2716 game rom at IC14.  This covers most games (except Firepower).  If you do this you do not need to replaced the sockets for IC21, 22 and 26 as you'll never (I know, never say never!) use them.

The LED that has been added to your driver board is a blanking signal indicator by the look of it - do you find it any use?

As a thought what about a super cap and removal of D17 for the battery replacement?  About the same cost as batteries and a long time maybe more elegant solution.  It seems popular in the Bally world, but not in WMS which I don't understand.

[Homepin]

Acetone man I thought that stuff ate everything.   I'll have to give it a try I hate the white residue

Acetone works fine - I use a toothbrush and scrub the 'fluxed' area vigorously then (using the toothbrush) I sweep the excess liquid (now laden with disolved flux) off the edge of the board with fast, repeated sweeping motions - it dries very quickly and doesn't affect screen printed legends etc.

[Steevsee]

Thanks Firepower. Nice to hear your thoughts

I find the whole rom / prom changing story confusing and Clay's guide whilst great and very generously provided would benefit from some quality editing to make them more readable and usable. So much info is repeated and placed in ad hoc locations. 

Agree 100%. But they are still an extremely valuable resource. 

The LED that has been added to your driver board is a blanking signal indicator by the look of it - do you find it any use?

Yes. I actually installed it whilst trying to get the CPU running and found it a good visual indicator as to what was going on.  I guess I was used to a blanking led from my last system 11 repair.

As a thought what about a super cap and removal of D17 for the battery replacement?  About the same cost as batteries and a long time maybe more elegant solution.  It seems popular in the Bally world, but not in WMS which I don't understand.

I do like the idea of keeping the board nice and tidy.  Will definitely look into this for future.  Are there any drawbacks to these capacitors?
I know that you have to power them up regularly to maintain the charge but that's hardly a drawback.

[FirePower]

As a thought what about a super cap and removal of D17 for the battery replacement?  About the same cost as batteries and a long time maybe more elegant solution.  It seems popular in the Bally world, but not in WMS which I don't understand.

I do like the idea of keeping the board nice and tidy.  Will definitely look into this for future.  Are there any drawbacks to these capacitors?
I know that you have to power them up regularly to maintain the charge but that's hardly a drawback.

Super cap issues, as I see them;
 - at 5.5V they are slightly higher voltage than 3 x 1.5V alkaline cells but 5101 spec sheet says this is ok (good for 7V)
 - Loss of originality if this is an issue to you or subsequent owner
 - removal of D17 may cause some grief if someone reverts to batteries at a latter date and doesn't spot this
 - harder to reset to factory defaults - have to use dips rather than just remove battery
 - said to hold charge for about a month
 - I did read somewhere that they can leak - I've not seen this, but could remote mount
 - I wonder if it causes an issue when doing work on the board and remove the 5101 as it will be powered unless you remove the cap? maybe an argument to remote mount?

I have a Flash I'm working on at the moment and plan to do all the board work so I plan to try it on this and will report.

[Strangeways]

Great work 

I think it is great to see the hours put into these old boards bear good results. Interconnect and ROM sockets are a must on SYS4/6 Boards.

I'm looking forward to more updates !

[Homepin]

As a thought what about a super cap and removal of D17 for the battery replacement?  About the same cost as batteries and a long time maybe more elegant solution.  It seems popular in the Bally world, but not in WMS which I don't understand.

I do like the idea of keeping the board nice and tidy.  Will definitely look into this for future.  Are there any drawbacks to these capacitors?
I know that you have to power them up regularly to maintain the charge but that's hardly a drawback.

Super cap issues, as I see them;
 - at 5.5V they are slightly higher voltage than 3 x 1.5V alkaline cells but 5101 spec sheet says this is ok (good for 7V)
 - Loss of originality if this is an issue to you or subsequent owner
 - removal of D17 may cause some grief if someone reverts to batteries at a latter date and doesn't spot this
 - harder to reset to factory defaults - have to use dips rather than just remove battery
 - said to hold charge for about a month
 - I did read somewhere that they can leak - I've not seen this, but could remote mount
 - I wonder if it causes an issue when doing work on the board and remove the 5101 as it will be powered unless you remove the cap? maybe an argument to remote mount?

I have a Flash I'm working on at the moment and plan to do all the board work so I plan to try it on this and will report.

A supercap is the same as any other capacitor when it comes to the voltage rating. Most are rated at "5.5V" - meaning the MAXIMUM voltage that may be applied is 5.5V. Look at ordinary electro caps, you happily fit a 63V rated cap in place of a 16V rated one. Same story here - the Supercap will only charge to the voltage applied to it, if you apply 3.6V then that is what it will charge to.