CPC 6128 "Cost-down" MC100A mainboard appears dead ?

[00WReX]

Hi All,

I just received this morning a CPC6128 with the cost-down MC100A mainboard.

It is the only one I have got with that mainboard, but when I power it up (from a CTM-644 that I use with another 6128) I get nothing appearing on the screen.

No Border or colour change to the screen...nothing, just blank like the CPC is switched off. The LED on the CPC does come on though.

I only have basic things to test with (multi-meter), is there anything to check or prove the 100 pin Gate Array is functioning ?

I have done some initial basic tests...bypassed the on/off switch by placing a shorting jumper on the pins where the switch connects.
Checked the 5v at all the RAM chips. Tested that no chips were getting hot, and swapped the Z80 into another CPC and that worked.
I tried hitting the DEL key when first turned on but no beep from the speaker...so it does appear dead.

So really I'm thinking the culprit could be either RAM or the Gate Array at the moment.
Just wondering if there is anything to check before I start down the road of desoldering all the RAM chips only to find they were OK.

I would really love to get this CPC up and working as it is a Cost-down MC100A mainboard, Made In Thailand CPC and to top it off is a Spanish version with Spanish keyboard/case markings & ROM etc. (This would finish my Spanish collection already having a Spanish 464 & 472).

Beleive it or not it was sourced locally in Australia (well Tasmania and I'm in Victoria) and initial indication from the seller was that it powered up on a friends Amstrad Monitor. The seller was not around to see the power up though but has been really good and refunded the money for the CPC.

Any tips or pointers for this type of mainboard would be appreciated.

I'm afraid it may be the Gate Array and unable to be easily resurrected...

Cheers,
Shane

[Bryce]

What's an MC100A ?? Is it the Pre-ASIC version? Can you post a picture?

The first thing to check would be whether the CPU is getting a clock signal, but you can't check that with a multimeter.

Bryce.

[00WReX]

Hi Bryce, the mainboard is the MC100A.

Like this...

http://www.cpcwiki.eu/index.php/File:CPC6128_PCB_Top_(Z80330_MC0100A).jpg

Cheers,
Shane

[Bryce]

Ok, I just realised you were missing a zero: MC0100A.

Does it react when you insert a disk? Is there any voltage appearing on the Sync pin of the monitor socket?

Bryce.

[00WReX]

Oops yes, I missed a zero    MC0100A yes...

OK, no reaction from the drive when a disk is inserted and pin 4 on the J101 video connector is 4.78volts.

Cheers,
Shane

[Bryce]

Ok, that's good, but without an oscilloscope it's hard to know whether it's pulsing or constant. What about the RGB pins, have they any voltage on them? The clock signal to the CPU needs to be tested too, but you'd also need an oscilloscope to do this.

Bryce.

[00WReX]

The RGB pins have around 170mv.

Sounds like I'm stuck without the oscilloscope. And as much as I would love to get this board up and running, it's probably not worth the expense.

Cheers,
Shane

[Bryce]

It very likely that it's the ASIC that has failed. You can send it over if you like, but the chances of reviving it are very slim.

Bryce.

[00WReX]

Thanks Bryce.
I would need to work out what the cost is to ship the MB to Germany and back and determine if it is worthwhile.
I'm assuming if the Gate Array / ASIC is found to be dead that even if you could replace it, trying to source a replacement would be a challenge itself ??

Maybe I'll place a "wanted" to see if by some chance someone has a MC0100A MB surplus to requirements 

Cheers,
Shane

[Bryce]

Yes, the chances of finding a replacement ASIC is zero. And the chances that it needs a new one are about 80%.

Bryce.