[Mart]

Hello folks, after weeks of none stop working I finally got round to constructing the power supply.
I purchased a chassis mount transformer with 240 vac primary with 0 6 0 6 twin secondaries at 50 va 4.7 amp.

The 2 outer wires were used for 0 vac and 12 vac with the 2 inner wires linked together for the 6 vac centre tap.

On powering up the GrandMaster the machine comes alive to the point where the motor arm will move but it will only go to the top right hand corner and there it stays witht he GM making a fairly loud buzzing noise.

There are no lights of any kind so i am leaning towards the machine itself having a fault of somekind.

My only doubt and this is where you electronics guys will be able to help is with the power supply itself.

A voltage test shows when the machine is in use that there is 14 vac on the 12 vac feed and 7.1 vac on the 6 vac feed from and to the GM from the transformer.

Would this slight overload 14 vac and 7.1 vac instead of 12 vac and 6 vac on the supplies be enough to stop the GM from working properly or is there a tollerance witht these things?

I can actually get a proper power supply shipped in from the USA but it will be around £50 with the shipping and obviously do not want to do that if it is the machine that is faulty.

Any help much appreciated.
Thanks.

 

[nfman]

This has finally bubbled near enough to the top of my list again for me to get on with.

Mart: If you're still listening, those values are very similar to what I was seeing unloaded. I didn't test what the voltage/current were while it in use, but I'll see if I can find my multimeter and do so.

Righto... here's the story.

After I'd found the transformer I wanted to use, I took it down to the local swap meet/car boot sale/whatever-they-call-them-where-you're-from to find something to house it in.

My ideal case needed to have: Both mains and low-voltage cables, room for the transformer and a built in power switch. What I ended up with was this:



If you're into retrocomputing, you may notice the brand. I've saved the innards just in case I ever need to turn it back into an A1200 power supply.

The PCB was designed to fit in this case - many thanks to (*steve*) for advice on the layout. The board was made using toner transfer (blue film), an iron and some ferric chloride (you get the idea). Here are some pictures:



For the business end of the power suppy,I reused the connectors I scavenged from a Molex connector, fashioning them into a makeshift plug with a small wooden offcut I had laying about.

One of the links I posted earlier has the dimensions of the connector. I redrew this in Inkscape (a free vector drawing program), printed it out and glued it to the piece of wood. I wasn't too careful about hole sizes, but I did pick a pair of drillbits which looked like they'd match the outer diameter of each half of the molex metal bits. The smaller hole was drilled all the way through, then I enlarged it - to a depth that seemed right - from the back using the other bit. This seemed to work to keep the connectors roughly positioned at an appropriate depth. I then used an abrasive drum mounted on my rotary tool to roughly shape the wood to the correct outer dimensions to fit the chess computer's power socket. Much experimentation was involved.

Once I was satisfied it was an appropriate size, I siliconed the back, then haphazardly (and foolishly) wrapped it in electrical tape before it had set.

In the end, this is what I had:



The fluff, gunge and animal hair that it got coated with while curing was… umm… deliberate. To add character. Or something


In all, it seems to work fine. Given the chess computer is stationary, I don't have to worry too much about it moving about, which probably helps.

I'll leave you with a blurry, end-on shot of the connector which you can use to frighten small children and pets with:





Hope someone finds that useful.

Tim

 

[(*steve*)]

This has finally bubbled near enough to the top of my list again for me to get on with.

Only 7 months Tim, not bad

 

[nfman]

Yes, well, it spent most of that time being my #1 priority... which explains why it never got done

 

[Mart]

Yes, well, it spent most of that time being my #1 priority... which explains why it never got done

Hello Tim.
Yes still around and you gave me enough information before to get a power supply up and running.
Sadly there turned out to be some existing damage to the plastic circuit board which I only discoverd later so I'm afraid this Milton Bradley is very much RIP because there's little or no chance of these types of circuit can be repaired as far as I know.
It is in a cupboard and may be of some use to someone for spares as everything else sems fine.

By total chance I speculated on a Fidelity Phantom 6100 that has very little information about it and when it arrived it turned out to be unused still with the plastic cling film protection in place over the board.
The pieces were in the original untouched box and a lot of documentation on this model and the Fidelity Bridge Challenger and the original UK power supply.
In my house with the grand kids regular visitors I have decided to sell it on to someone who will be able to use it.
I have carefully peeled the cling film 3/4 back and played one auto game and one where I checked all the squares and keys and everything is perfect and does she look good or what !!!
How it has gone unused all this times beats me.
It is on the Bay and ends tomorrow lunch time.

Thanks. Mart.

 

[nfman]

Wow - that Phantom looks fantastic. It's a shame I no longer live in your general vicinity and aren't really much of a chess player. Nor am I able to afford what I reckon it'll fetch! If you're planning on getting rid of the broken one, I'd be interested in the pieces... but we should probably discuss that via private messages [Moderators: sorry if this is against forum rules - feel free to edit appropriately, or soundly chastise me].

As well as the power supply, my machine was missing a rook, so I ended up making this:



Straying away from electronics a bit - but for the benefit of anyone who stumbles across this thread looking for other "repair" tips for these - here's how I made it:

First, I pulled a small neodymium magnet off the fridge. Everyone has a few of these cool things laying around, right? If not, you want a small powerful magnet.

I then used some polycaprolactone plastic to shape something that would vaguely pass for a rook. Polycaprolactone is great stuff. It melts at about 60 degrees C, so you can heat it in hot water, then shape it while it's warm. It's sold under many brand names, but the one I used was called Polymorph.

After creating the general shape I wanted, I checked the polarity of the magnet against an existing piece. You want the side that repels to face the bottom of the new piece or it'll try to jump away from the board when the robotic part tries to move it.

I reheated the bottom of the piece by suspending it in hot water until it softened, then inserted the magnet to a sensible depth. I had to reheat and reposition the magnet until it worked reasonably well.

The new piece works surprisingly well for a bodge, and the plastic is smooth enough that I wasn't worried about it damaging the membrane during play. As an aside, I had great fun playing with lower strength (the dark ferrite-looking type) magnets in place of the pieces and watching them jump. I wasn't brave enough to play with a NIB one, in case it gouged out a path when it moved.

 

[Mart]

Alas no pieces came with the original unit just the board.
There used to be a place in the US that advertises the pieces individually but I am unsure if they are still trading or not.
Suprisingly little interest in the Fidelity unless someone is waiting but I am not overly concerned it is just a real wrench to let it go.
Thanks. Mart.

 

[nfman]

Alas no pieces came with the original unit just the board.

No problem. I discovered an article on one of the Polycaprolactone vendor sites the other day which describes a method for dying the plastic - so I'll hopefully have a correctly coloured (but still merrickesqe) rook at some point