MTX 512 (debugging thread)

GozdniJezek
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Re: MTX 512 (debugging thread)

Post by GozdniJezek » 10 Jun 2019 08:56

First of all, sorry for late reply and thank you for your answers.
1.) Regarding EEPROMs it sounds like a good idea but the friend does not have an EEPROM burner yet. So this suggestion will have to wait, I'm also reluctant in modding the machine before i get it to a working order. (However i saw somewhere that there is a diag cartidge, that i can connect externally, would this also boot, if the CPU is ok?) i prefere the external option if that is even possible.

2.) I'll focuse on the video memory first. Thank you for the suggestion.

3.) Can you please elaborate on GAL solution? If i understand correctly, I should firstly restore the machine to MTX500 state and than go from there? Is this trivial or it needs some work? What is the bill of material and is there any reference on how to do it? I see that i should "putting the PAL back in without the extra board and changing LK7 from the '4' position to the '2' position and LK6 from 4-C to C-H (as he has the 'H' specification OKI RAM chips) would do that" - Where can i find the original PAL-A chip specifications? And can someone please elaborate what a LK7 and LK6 are? Or please reference me to the appropriate documentation.

4.) I also noticed the traces, will need to check for continiuity. Thank you.

5.) I've checked the Operator’s manual, for starters i was hoping for something like MTX Technical Specification, 1st page just in high resolution, as i need to learn what is what firstly. :) Does something like that exists?

6.) Not shure to what i'm refering in the PCB location, is there any reference, which will help me understand the layout? Or is it just a column/row kind of thing? From left to right based on chip order?

7.) If I understand correctly, i shoud also hook up the Hi-Fi (sound output) if boot sequence is started i should hear a tone? And test with <Control><G> for output. This is really trivial and i'll try it. Thank you.

8.) Can you please elaborate what a VDP is? Is it a video chip? Are ROMs prone to failure, can "originals"(non EEPROMS) be easily sourced? To test this, could i get away with the diagnostic cartidge?

9.) "The replacement chip in 9D is a CMOS (HC) device, rather than the original high speed TTL (S) chip." - I presume this refers to the soldering/replacing IC marks and is related to point 10?

10.) Will try to make a sence of the mod from page 47 of the manual and post additional pictures to confirm this.

Thank you all for all of your suggestions, I'll go through them and post the updates, but I can't guaratee that they will be regular or often, as RL gets in the way. :)

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Dave
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Re: MTX 512 (debugging thread)

Post by Dave » 10 Jun 2019 09:37

Point 1.

At the moment, Martin has the only external diagnostic “cartridge”.

I will be producing a PCB to allow me to build others, but that is a few weeks away, say 3 weeks.

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Re: MTX 512 (debugging thread)

Post by Dave » 10 Jun 2019 09:42

Point 3.

Download the Service Manual from my Manuals Page http://www.primrosebank.net/computers/m ... anuals.htm

The Link positions are shown on page 48

The PROM on your “bodge” board looked to be the original. It should work if put back in the original socket and the links set as shown in the Service Manual for your board revision - the board revision is marked at the right hand side of the PCB.

The original PAL equations are given in the Revised Operator’s manual, the Phoenix one, on Page 249

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Re: MTX 512 (debugging thread)

Post by Dave » 10 Jun 2019 09:47

Point 5.

Don’t understand the question? What do you need that is not in the (very clear) copies of the circuit diagrams on my site or in the revised Operator’s manual (the Phoenix manual)?

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Re: MTX 512 (debugging thread)

Post by Dave » 10 Jun 2019 09:48

Point 6.

The layout matrix is stencilled on the PCB, letters on the bottom for the columns, numbers on the side for rows

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Dave
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Re: MTX 512 (debugging thread)

Post by Dave » 10 Jun 2019 09:53

Point 8

As asked . . . .

Video Processor,
Yes,
Not particularly prone to failure, but it does happen
No, the original Mask ROMs are unobtainable
Yes

stephen_usher
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Re: MTX 512 (debugging thread)

Post by stephen_usher » 10 Jun 2019 10:20

To clarify 3)

To return the machine back to MTX500 configuration you will need to look at the links near the PAL board marked LK6 and LK7. These are made using "loops" of wire soldering into holes on the circuit board.

At the moment LK6 is set so that the '4' and 'C' holes are linked. You will need to desolder this wire, clear out hole 'H' with de-soldering wick (I like the "Soldermop" brand) and re-solder the wire between 'C' and 'H'. You'll be linking to the 'H' position as you have 'H' marked OKI RAM chips, which have been tested in the factory to work in the upper half of their addresses.

Similarly, LK7 (a chip above LK6) needs to be changed from the '4' position to the '2' position.

Once this is done, remove the PAL from the hacked circuit board and put it into the socket where the board was plugged into.

This will completely revert the machine to the factory settings.

stephen_usher
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Re: MTX 512 (debugging thread)

Post by stephen_usher » 10 Jun 2019 10:22

Dave wrote:
10 Jun 2019 09:53
Point 8

As asked . . . .

Video Processor,
Yes,
Not particularly prone to failure, but it does happen
No, the original Mask ROMs are unobtainable
Yes
The video processor seems pretty robust.. mine survived high reverse voltages on the ground a couple of times and didn't blink!

GozdniJezek
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Re: MTX 512 (debugging thread)

Post by GozdniJezek » 10 Jun 2019 14:16

Thank you for the answers.
1.) If that will be ready to use or as a kit with all the components (preprogrammed ROMs) I would be interested in purchasing it.

3.) I will check the manual thank you both.
5.) I would like the high level schema (i'm not shure if this is the correct term for it), so i can identify things we're discussing:
MTX.png
MTX.png (934.67 KiB) Viewed 492 times
I can't read all of the text on this one. Sorry for confusion.
6.) Sorry, I did not notice it at first, this is a very nice feature! :) Thanks for pointing it out.
8.) Does any member on this forum/FB sell new EPROMS? Or does everybody have modoed machines for EEPROMS?

I will try the suggested solutions starting with the most trivial ones. Thank you once again!

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Dave
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Re: MTX 512 (debugging thread)

Post by Dave » 10 Jun 2019 14:48

Closest is probably the annotated PCB photo on this page http://primrosebank.net/computers/mtx/mtxphoto.htm

But if you use the matrix notation that I described, we will know what you are referring to

EPROMS or EEPROMS both need your PCB modified as previously described

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