Repair advices ?

About original Memotech hardware.
Post Reply
User avatar
Crazyboss
Site Admin
Posts: 230
Joined: 09 Aug 2012 21:45
Location: Sweden
Contact:

Repair advices ?

Post by Crazyboss » 09 Jul 2015 20:57

Hi.

Got a lot of MTX stuff, from another MTX fan, there was a board which I am trying to fix.

Its a 4000-4 board

When I try to turn it on (PSU is good), I get black screen and humming sound.

All 8 ram ic's are Socketed and replaced with KM4164b-12 ic's I guess it means that there should not be any ram ext. board at the right side ?

I did not replace the caps yet, but they are for sure the original 80's one, this might be the next step.

Any Clues what to try first ?
//CLAUS - Webmaster at www.mtxworld.dk

User avatar
Dave
Posts: 752
Joined: 11 Aug 2012 18:16
Contact:

Re: Repair advices ?

Post by Dave » 09 Jul 2015 21:26

Hi Claus

I'd still suspect the RAM.

Was this an MTX500 to 512 upgrade?

If so, has the memory PAL been changed - see the service manual for how to identify the correct PAL and motherboard links for each memory configuration

Have you checked the RAM chips in a known good system and/or tried swapping them?

Have you checked for bent/missing pins?

Check for continuity/shorts using the circuit diagram in the MTX manual

A RAM board would be supported, depending on the PALs on the mainboard and RAM board, but you should remove it for testing

regards
Dave

User avatar
Crazyboss
Site Admin
Posts: 230
Joined: 09 Aug 2012 21:45
Location: Sweden
Contact:

Re: Repair advices ?

Post by Crazyboss » 10 Jul 2015 11:59

Dave wrote:Hi Claus

I'd still suspect the RAM.

Was this an MTX500 to 512 upgrade?

If so, has the memory PAL been changed - see the service manual for how to identify the correct PAL and motherboard links for each memory configuration

Have you checked the RAM chips in a known good system and/or tried swapping them?

Have you checked for bent/missing pins?

Check for continuity/shorts using the circuit diagram in the MTX manual

A RAM board would be supported, depending on the PALs on the mainboard and RAM board, but you should remove it for testing

regards
Dave
I got the board from another MTX Friend, so I do not know what was done before. It could be someone wanted to upgrade it from 500->512 without use the add-on board ?, since all the RAM IC's are now in sockets. Not sure if the PAL have been changed or not.

As far as I know those RAM IC's need 12v too, maybe something wrong with the 12v line, but then the SOUND should be silent I guess ?

I will try to check the voltages too.

Where is a good spot to test?

After the Regulators?

I just used 5 mins yesterday didn even check the fuse :) But I think I can get the board to work.

Actually I now have around 5-6 boards laying around, none work 100%

The most strange case I have is my -06 board which works when the roms are plugged in but dont work with the rememorizer, it have worked before with the rememorzier, but suddenly its like dead. Then I put it back to original state, by plug in the roms and removed the Rememozier, and it works great, can load from tapes (wave files, etc) but not use it with the rememorizer, the rememorizer work great with another board, with the same PSU used. Strange. Wonder If I could have damaged something on the board so it can not use add-on cards ?
//CLAUS - Webmaster at www.mtxworld.dk

User avatar
Dave
Posts: 752
Joined: 11 Aug 2012 18:16
Contact:

Re: Repair advices ?

Post by Dave » 10 Jul 2015 13:02

Claus,

Pleeeeeeaaaaaase look at the circuit diagram for the MTX.

With the power off :

Use a meter to check that all of the address lines are connected to the correct pin on each of the DRAMs and that there are no short circuits, either between the address lines or any other pins on the DRAM. Reach of th address lines should connect to same pin on all of the DRAMs, e.g., MPA7 should connect to pin 9 on all of them.

Do the same checks for RAS, CAS and WR.

Similarly, check that the data lines connect to a single RAM and there are no shorts between the data lines or any other pins. Each data line should connect to two pins on one, and only one, of the DRAMs.

The circuit diagram will also show you where you can check +5v and 0v on each of the DRAMs. Check for continuity and shorts with the power off, then you can check the voltages with the power on.

The circuit diagram would also show you where +12v wasconnected to the DRAMs! (Or not, as the case may be)

Please look at the service manual, it will tell you how the RAM select links should be set and the colour of the PAL. If the PAL is original, it should have a coloured sticker on it.

Please confirm the link positions and the colour of the PAL.

If you have a known good memory card, you could remove the on board DRAMs from their sockets and try it with just the expansion RAM card.

Regards
Dave

User avatar
1024MAK
Posts: 564
Joined: 24 Dec 2012 03:01
Location: Looking forward to summer, in Somerset, UK

Re: Repair advices ?

Post by 1024MAK » 10 Jul 2015 13:08

KM4164b-12 DRAM chips only require a single +5V supply. The only memory on a MTX board that requires three supplies (+5V, +12V and -5V) are the chips used for the video RAM.

There are no specific chips used for the expansion connector. Check/clean the edge connector contacts.

When trying to use the rememorizer, is your configuration one that needs a different PAL/GAL fitting?

Mark

User avatar
Crazyboss
Site Admin
Posts: 230
Joined: 09 Aug 2012 21:45
Location: Sweden
Contact:

Re: Repair advices ?

Post by Crazyboss » 10 Jul 2015 19:53

i tried to take the pal out it didn have any mark on it and replaced it with the one from the -06 board (which have 64k onboard).
then I got the -04 board booting, but it started in panel, and then blue screen etc.

then I put back the original PAL and then it started in Basic with the READY prompt, maybe it was a bad connection in the pal socket ?

I think one of the pals is 2CN and another one was 4CN ? the one fitted at the -06 board was marked with a red label.

I only used limited time on that project hope durring my upcomming hollydays can get time for doing more MTX work, but I do think (I AM SURE) WIFE have a list to :( Among those is Putting FIREWOODS to the garage and something about changing the WALL PAPER :( funny she did not mention anything about retro computer fixing ?

Also I would like to get time to visit http://www.destinationhalmstad.se/engli ... s-2015.htm
//CLAUS - Webmaster at www.mtxworld.dk

User avatar
Crazyboss
Site Admin
Posts: 230
Joined: 09 Aug 2012 21:45
Location: Sweden
Contact:

Re: Repair advices ?

Post by Crazyboss » 12 Jul 2015 13:24

still working on the -04 main board. Today I changed the Cap (above the heat sink) and changed the TIP also, not cause it was bad but cause I got new ones which are more isolated than the original ones. The new one is plastic everywhere, not including the space where it touch the heat sink, but I used the original isolator material here.

Wonder why but all the MTX's I have seen only had the heat sink plate, which connect to the alu.case when the computer is assembled. But my -06 mainboard have also a block monted at this heat sink plate, and the -04 here also had that option. Cause I have a hole so you can mount extra heat sink but I do not have the extra heat sink block or maybe the previous owner made that hole.

I think all Memotech USERS now a days wish that Memotech had made the PSU deliver the req. voltages outside the computer case, of cause the PSU might be a bit larger, but if we could get rid of the regulators and power caps could be nice.

I wonder if the memotechs was shipped with only that plate as a heat sink and ofcause make sure its touching the black case, to spread the heat? or had some of you ever seen extra heat sink blocks mounted on the plate ?

Actually I am not sure the plate have very great contact with the computer case plate.

I also took the CPU, CTC, PAL and VDP out and spray with electronic cleaner spray before put them back into the sockets.

The computer didn refuse to start, so keep my fingers crossed it works now. The Dram is's are nice cold (running a few minutes) the VRAM original not socketed 4116's some are hot and others are not, I guess its quite normal.
//CLAUS - Webmaster at www.mtxworld.dk

Martin A
Posts: 417
Joined: 09 Nov 2013 21:03

Re: Repair advices ?

Post by Martin A » 13 Jul 2015 19:41

Don't forget that there should be a bolt running through the bottom of the case to one or more of the regulators. (the 5v regulator has the long bolt on both of mine)

In addition to holding the heatsink in contact with the case, the bolt itself would help transfer heat to the case.

Post Reply