Another MTX Fault - Jon Riglar's MTX

About original Memotech hardware.
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Dave
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Re: New member saying hello

Post by Dave » 14 Aug 2015 14:03

Hi Jon,

OK - thanks.

Which item was it ?
It should be on this page . . .
http://www.primrosebank.net/computers/mtx/mtxsales.htm

If the item was really "not as described", have you raised it with the seller and/or ebay?

A good check on whether the CPU is running, even if the video is not working, is to try to get a sound from the machine.

Either through the TV, or with the audio out connected to something, hitting <CTRL><G> should give you a "ding". If you get no sound, it's a good indication that you have bigger problems than the video

regards
Dave

jonriglar
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Re: New member saying hello

Post by jonriglar » 14 Aug 2015 14:41

Hi Dave
A quick look at the webpage link and my advert/machine isn't listed there.

I'll dig out more info (serial number, etc.) later.

I didn't pay too much for the machine, and was aware there was likely to be some TLC required. I understood it was listed as 'for spares', so no complaint there. My main beef was with the description 'this was switched on about twice when it was new and has sat in some original packing in the loft since'. The case screws were loose, and clear repair work had been attempted - there is even what appears to be a 1980s repair shop sticker intact across the top of the ROM chips. I've exchanged messages with the seller and suggested his description was more than slightly disingenuous but his attitude was pretty much 'I sold it as spares' so tough!

Not going to loose sleep over it, as it has the makings of a very good condition machine when repaired.

Thanks for the tips on remedial action!
Regards
Jon

jonriglar
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Re: New member saying hello

Post by jonriglar » 14 Aug 2015 16:43

Serial Numbers is 512/25525
I seem to have suddenly found a constant 'tone', but pressing CTRL + G makes no difference; probably because the tone is already constant?!

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Dave
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Re: New member saying hello

Post by Dave » 14 Aug 2015 16:59

Hi Jon,

the constant tone (with a black screen) is a common symptom of a main RAM problem.
(Although, other "fatal" problems could cause this too.)

I take it that you have changed the RAM?
This is the problem that Andy Key and I saw when we tried to upgrade MTX500s to MTX512s by removing the 32K RAM and adding 64K. Martin Allcorn has now done two of these upgrades (using my RAM chips) and has had no problems. I subsequently went back and rechecked mine and I found that I had broken a trace when I did the change.

see this page http://www.primrosebank.net/computers/m ... pgrade.htm

You might want to check for continuity between all of the RAM pins (apart from the data line, pins 14 and 2), all of the rest should be connected.

As an aside, even though it said MTX512 "on the tin", it may not have had 64K on the board?
Were the chips that you removed definitely 64K chips - what was marked on them?
If you have upgraded from 32 to 64, you will need to change the memory PAL
(That would not prevent it from working, just seeing the extra 32K)

regards
Dave

jonriglar
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Re: New member saying hello

Post by jonriglar » 14 Aug 2015 22:40

Hi Dave
I haven't changed the main RAM. It's definitely a 64K set up. Following your advice I've checked continuity on the main RAM chips and all is fine.
I've only changed the VRAM chips.
Regards
Jon

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Re: New member saying hello

Post by Dave » 14 Aug 2015 23:16

Hi Jon,

OK, as I said, the symptoms are typical of a RAM fault, but it could be pretty much anything. If you have spares, it's easy to swap the Z80 and CTC, everything else is socketed.

No guarantee that it would fix it, but changing the RAM is the best bet. You have a couple of options, depending on how comfortable you are taking a soldering iron to the board. If you're OK with that, then that's a good plan. If you are less confident, Andy Key has a very inexpensive memory card for sale on his site.
http://www.nyangau.org/memcard/memcard.htm


Mark Kinsey used it to diagnose the memory fault on his machine
http://www.primrosebank.net/computers/m ... repair.htm

regards
Dave

jonriglar
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Re: New member saying hello

Post by jonriglar » 14 Aug 2015 23:25

Hi Dave
Happy with a soldering iron, so would be ok swapping out old for new chips - and into sockets.
Do you stock suitable chips?
Thanks
Jon
PS I realise this probably shouldn't be in the Introductions thread!

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Re: New member saying hello

Post by Dave » 14 Aug 2015 23:33

Hi Jon,

OK - fair enough.

Have I confused you with the Jonathan Riglar that just bought some RAM from me off ebay?

The ones I have on there are tried & tested with MTX repairs, i.e., they are the ones that Martin and I used.

As you say, it's a bit off topic, I will move the thread I think

regards
Dave

jonriglar
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Re: New member saying hello

Post by jonriglar » 14 Aug 2015 23:36

Hi Dave
We are one and the same - only my mother still calls me Jonathan lol!
Jon

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Re: New member saying hello

Post by Dave » 14 Aug 2015 23:37

:-)

OK - so the RAM you bought wasn't for the MTX then?

regards
Dave

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