Saitek Corona electronic chess computer repair

[technicalspecialist]

I am currently trying to repair a customer's Saitek Corona electronic chess computer originally from 1987.
More info: https://translate.google.co.uk/trans.../Saitek_Corona

It requires 9VDC from 6 C size batteries or a 9V transformer via the 2.1mm barrel connector. He told me that he accidentally connected 30VDC to it and 2 electrolytic caps exploded.
It no longer works properly but its not completely dead though. I can turn it on by pressing Play and Go buttons together, which is the normal way to turn it on. Some LEDs light but it doesn't do anything else.

On the board there is a transistor-zener regulator that regulates the input voltage to 5V for the ICs. I replaced the exploded caps and tested all 1N4148/1N4007 diodes and transistors.
They tested OK with 0.6V drop on my multimeter in diode mode.

I've attached high resolution photos of the board and ICs.
The CPU is a W65C02P.
The RAM is a AS6C6264. I replaced the original but that made no difference. Same symptoms.

The program EPROMs are 2 UV erasable HN27C256AG-10's. They have stickers over the windows.

There are 2 large ICs labeled NEC 8919KX GAl (C) '87 SCISYS 184. The I could be an uppercase i, a 1 or lowercase L - im not sure.
I can't identify what these NEC 8919KX GAl chips are. I can't anything useful at all on Google. Certainly no datasheet.
On the board HELIOS is silkscreened next to them. I don't know what that means.
As they're large and there's 2 of them I think they might be I/O expanders or ASICs? Does anyone know what they are?

There is a 5.000MHz crystal on the board connected to one of the 8919KX GAI chips. When i probed it, i DID get 5.000Mhz on my multimeter so that IC appears to be working ok.

When I supplied 9VDC from my bench PSU to the barrel jack, i got 5V across the 100n ceramic bypass caps for the ICs.
So the transistor - zener is regulating and the 5V rail is not shorted. i get 70mA current draw at 9V on my bench PSU.

I don't know how to proceed further. I could buy a replacement W65C02P on eBay from china but they might be fake.
i think I read somewhere that there were/are a few different variants of the W65C02 and not all support the same instructions. Is that true?

If the EPROMS and/or the NEC 8919KX chips are corrupted/fried, there isn't really much i can do.

I can't find ROM images online so even if i ordered new EPROM chips, i wouldn't have any image file to program them with. I'd also need to buy a TL866II plus programmer, which is £38.30
Does anyone on here happen to have the same model chess computer and could read the ROMs for me? If i could get ROM images, it might be worth buying the programmer.

Links to items on eBay
W65C02: https://www.ebay.co.uk/sch/i.html?_f...c&LH_PrefLoc=2

27C256 ROM: https://www.ebay.co.uk/sch/i.html?_o...7C256&_sacat=0

TL866II Plus programmer: https://www.ebay.co.uk/itm/141701435348

[redwire]

Re: Saitek Corona electronic chess computer repair

The reverse-polarity diode is after the 1,000uF capacitor, so perhaps polarity was reversed so the cap popped. But there is a 1k resistor too going to some stuff, and lots of transistors for power management. Z1 seems to be the main zener. A discrete zener-transistor regulator would still work with 30v input, so it might not have gotten overvoltaged?

With old 8-bit computers, I scope the data, address and chip selects, crystal osc etc.
You can check for activity, if ROM or RAM is being accessed. A bad IC will have a crappy signal swing and not a full 5V square wave.

[technicalspecialist]

Re: Saitek Corona electronic chess computer repair

Ok, i will scope the CPU, RAM and ROM. The 1000uF cap and the black cap are the new ones i put on.
The originals were 100uF 16V so 30V definitely would have poped them whether the polality was reversed or not.

The BD438 is the main regulating transistor. At least some if not all of the TO-92s next to it along with the resistors and small blue capacitors (10uF) form some sort of latching power on circuit i think. There is no 5V output from the BD438 until i press the 2 buttons mentioned above.

I am not sure what the purpose of the 1K resistor is.

The circuit is difficult to understand because the transistors are a mixture of NPNs and PNPs and there are traces on the other side of the board that go off to various places and it is not layed out neatly. I wish i had a schematic but i don't.
i haven't reverse engineered a schematic before but i will try to reverse enginneer the power circuit.

[redwire]

Re: Saitek Corona electronic chess computer repair

I forgot to mention looking at RESET, I'm not sure who is generating it. It might just blip after the BD438 turns on. It might be U10 MN1280 doing it or that is to protect SRAM contents during power down, if this has a battery somewhere.

[CapLeaker]

Re: Saitek Corona electronic chess computer repair

I wonder if only one of the 27C256's is bad. To me it looks like the machine boots each time you start it from the EPROMs. I don't think that there is a "memory battery" in this thing. Interesting is that it actually has two 27C256's in there. I don't think that the CPU reads both chips at the same time. So probably it reads the first one o.k. and then stalls on the second one. But then on second thought, why not using a single 27C512?
Anyway, I did figure out that the "Endgame ROM" (another third 27C256) and another RAM chip are not installed on this unit.
I also know that other computerized chess boards from this manufacturer use a single NEC 8730KX IC. I am not sure, but maybe these NEC's are something like a SIO (serial in / out) or PIO (parallel in/out) or CTC (counter timer channels) etc IC's since the data lines (bus) from the CPU go right to it? Its probably something similar to a CTC...

[ReverendJones]

Re: Saitek Corona electronic chess computer repair

On the NEC chips, 8919KX is a house number. These are GALS (Generic Array Logic or Gate Array logic). They were custom made/programed for SciSys, a manufacturer of chess computers at that time.

[kc8adu]

Re: Saitek Corona electronic chess computer repair

too bad checksum not on eproms so you can verify.
maybe someone can dump theirs for you .
or is the unit that rare?
i have a few chess computers in my collection but dont recall one like that.
would also be nice to get a dump of the option rom.
i would trace dc input to everywhere it goes in case some section runs on the +9v and got damaged.
and with a bit of luck you might identify some rebadged units like for radioshack,dak,ect.

[stj]

Re: Saitek Corona electronic chess computer repair

maybe it's in MAME.

[rmraovich1978]

Re: Saitek Corona electronic chess computer repair

I have a Saitek Cougar that needs repaired, can anyone help or know anyone that can fix it? Needs capacitors replaced... thanks.