Hello from a new member

johnha
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Re: Hello from a new member

Post by johnha »

Thanks Dave,

I meant to type "I'd be grateful if somebody could point out _where_ the PAL/GAL lives?" which you have answered :)

It's not visible from the photo, but there is a break in the plastic under one of the RS232 port holes, suggesting it may once have had ports fitted. I've closed it up now but I can see scratches on the edge connector on my copies of the photos on the right-hand half of the connector.

BTW I needed a 2mm allen key for mine, thanks for the info on how to open it up.

John.
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Dave
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Re: Hello from a new member

Post by Dave »

Yes,

sorry John, it is 3mm screw with a 2mm Allen key head :oops:

regards
Dave
johnha
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Re: Hello from a new member

Post by johnha »

OK, I see the links 6 & 7 you mentioned on Pg 44 of the service manual. Looking at the photos it seems hard to believe that the links have been 'retro-modified' had a memory board been removed from the machine.

I presume the reference to a 'blue PAL' in the manual relates to the blue sticker.
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Dave
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Re: Hello from a new member

Post by Dave »

John,

I don't know whether a memory board made any difference to the links on the main board. I can check though, my original "MTX512" also had only 32k on the main board, with the extra 32k on a RAM card. I will have a look later.

Given what you said about the RS232 plastics though, it may be that the board installed, which left marks on the edge connector, was an RS232 card.

Yes, the colour relates to the sticker,

Regards
Dave
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Dave
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Re: Hello from a new member

Post by Dave »

Hi John,

my PAL does not have a colour code on it, but the machine has the same RAM chips as yours - 32k on board, plus an add-on 32k memory card. The positions of Links 6 & 7 are the same as yours, so that would suggest that whoever took the RS232 card out of your machine took a RAM board out too!

regards
Dave
johnha
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Joined: 16 Jan 2013 04:25

Re: Hello from a new member

Post by johnha »

Hi Dave,

I got the impression that Pg 44 of the service manual suggested that 64K machines would have different links (and/or PALs) than the 32K ones?

Unless there were two types of 64K machines, those with 64K on board and those with an add on card providing the other 32?

EDIT - I plan to open up the RS128 soon, let me know if there's anything you'd like me to photograph in particular.

John.
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Dave
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Re: Hello from a new member

Post by Dave »

Hi John,

I ran this by Andy Key (our Memotech hardware guru!), Andy says that the PAL only looks after the ROM/RAM on the main board. So a 32k main board with a given PAL and corresponding RAM chips would not be affected by an add-on memory board. That is consistent with our two machines, same main board RAM, same link positions and I assume, the same PAL. Both work fine, but mine has the extra 32k RAM board. I would have removed my RAM board to prove the machine was unaffected, but it is soldered I the main board.

RS128 photos would be great thanks!

. A nice high def photo of the keyboard
. High def photos of the boards, you might struggle to get them all in one shot, so Perhaps separate photos of the main board, RAM board and RS232 board may be required.

Could you also take a note if the boad rev number if it is not clear in the photos please?
If it is rev 4094-06, it should be a multi layered board, so an extra close up of the PCB tracks would be nice too.

Thanks a lot
Regards
Dave

p.s., could you do me a close up of your MTX PSU please? Although it is the same PSU as the rest, it does have a slightly different label that I'd like a copy of please
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AndyKey
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Re: Hello from a new member

Post by AndyKey »

Good set of pictures.
Looks in excellent condition.

REMEMOrizer could work with this, if you want it to.
Setup: remove 16KB ROM on bottom right, set REMEMOrizer ROMs jumper high, set REMEMOrizer MTX500 jumper high.

{{{ Andy
johnha
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Re: Hello from a new member

Post by johnha »

Hi Andy,

I'm a bit reluctant to start removing ROMs (on the basis they've been in there 30 yrs...), I note your site suggests that you can keep the ROM in situ but lose some functionality. Would I need to replace the PAL too?

Dave - I have yet to open the RS128 up (I need to find enough time), the PSU propping up the 512 in the photos is that one (it's not very clear). I have the box for the RS128 too, will get some of that as well. The photos of Flickr are my default 2MP shots, I have higher res versions (16MP), email me if you're interested.

Having taken the shots, I recommend it as a great way to inspect the circuit board - stick them on a decent monitor and you can see detail you can see whilst hunched over it at a jaunty angle...

John.
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Dave
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Re: Hello from a new member

Post by Dave »

Hi John,

if it sets your mind at ease at all, I have had the ROM(s) out (and in, and out) of 2 MTXs in recent weeks with no problems at all.

I have a "proper" IC removal tool, but I actually found it easier just to use a flat blade screwdriver and gently prise up the chip at both ends.

If anything, putting them back is slightly harder, but you just need to make sure that the legs are nice and straight and at the right angle. I find that slightly bending them, one side at a time, on a flat surface does the trick.

If you're careful, I can't see that you will damage the socket or the board, worst case (and I think it's pretty unlikely), you could damage the EPROM but it would be easy enough to get another one programmed

regards
Dave
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