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The Memotech MTX Series

MEMOTECH

- Maintenance / Repair

 

 

Hardware Problems ?

A copy of the Memotech Service Manual is available on the Manuals page. However, there are a couple of common problems that are worth noting before getting into the depths of the Service Manual - herewith the NODDY Guide to fixing your MTX!

For possible fixes to more serious problems, see my Repairs page.

Of course, any maintenance guidelines would not be complete without the obligatory safety warnings, so, if you are not fully confident with your abilities once inside the MTX or PSU case, and with apologies to anyone that actually speaks German,  . . .

ACHTUNG - ALLES LOOKENPEEPERS

Das Machine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitzensparken. Ist nicht fur gewerken by das dummkopfen. Das rubbernecken sightseeren musten keepen das cotten-pickenen hands in das pockets - relaxen und watchen das blinkenlights.

 

System
Black screen and continuous audio tone on power up This is very likely to be caused by a RAM fault.

These were the same symptoms seen when Andy and myself tried to upgrade our MTX500s to 512s and introduced a RAM fault.

Mark Kinsey diagnosed a RAM fault from scratch on an MTX512 with these symptoms. Follow this link to see how it was done.

Intermittent problems with your MTX? Random crashes etc?

Do you have any option boards fitted ?

If there is an extra memory card or an RS232 card etc. fitted internally, the edge connector often causes problems. This was a known problem for Memotech who often soldered the RAM board to the main board.

If you are suffering from unexplained problems, it is worth removing the option board, cleaning the main board edge connector and refitting the option card.

Video / TV
Display corruption present on both TV and video monitor with the rest of the computer apparently working. This is very likely to be caused by a Video RAM fault.

Follow this link to see how one user fixed the problem.

Display losing colour after a few minutes? This is very likely to be a fault on the video board.

Follow this link to see how one user fixed the problem.

No picture on TV at start-up or losing picture after a few minutes? The RF modulator is prone to drifting off UHF Channel 36 (in the UK). Mine seems to be getting worse with age. Try retuning your TV before doing anything else.
No picture on TV Can be caused by a faulty LM1889 modulator on the video board
Composite Video output is monochrome Check the position of the link on the video board, hidden below the large electrolytic capacitor, next to the oscillator.
Position "a" Colour signal from the LM1889
Position "b" Monochrome signal from the VDP
Keyboard
Keyboard problems - some keys not working? Whilst the problem could obviously be something more serious, the first thing to check is the keyboard connector on the main board. Check for broken wires, or problems with the wires into the plug terminals.
Keyboard problems - sticky keys or multiple characters?

This is very common, particularly if the MTX has not been used for a long time. The first thing to try is to give the keys a good workout, lots of tapping of the affected keys with a bit more force than normal typing can improve things markedly.

There are lots of potentially helpful tips for cleaning mechanical keyboards on the web, for example, Google "mechanical keyboard sticky keys", and you'll find items such as :

 

Toms Hardware

 

I have personally tried this, but it seems reasonable - use at your own risk though

Sound
No sound from Hi-Fi out On two of my three MTX's the connection to the "Hi-Fi" port on the rear of the case had broken - if you have no sound output on this port, check this first.
Others
Tape Loading problems Some obvious, but perhaps helpful, information can be found on my Tapes page.
Memotech Printer Ribbon

If you are lucky enough to find a Memotech DMX80 printer, you may need to source printer ribbons. The DMX80 was made by Panasonic and the ribbons are compatible with Panasonic printers, such as, KX-P1090, KX-P1080, KX-P1030 etc. Suitable printer ribbons can be found here.
MTX Power from Twin FDX

The twin drive FDX houses an internal transformer like that in the MTX PSU and provides power to the MTX using a cable with 240o, 6-pin, DIN plugs (with the centre pin missing). If you require a replacement cable, the BBC Micro RGB cable is widely available on ebay and can be used (the centre pin will not be used).

 

FDX Floppy Disk Drives - QumeTrak 142 5.25" Drive

A copy of the Qume Maintenance Manual is available on the Manuals page

Dirty heads. Gently wipe over both heads with a cotton bud dipped in isopropanol. http://www.lo-tech.co.uk
Sticky head mechanism The service manual states that a 50g weight attached to the head mechanism should be enough to pull the head to either stop, with the drive on end as required. In practice the head mechanism should move easily. It is prone to become sticky especially at the ends of travel, in which case the drive may fail a BIOS seek test (reporting floppy drive failure). This can be easily resolved by first cleaning the three rails thoroughly (again with cotton bud dipped in isopropanol) and then applying a little grease again with a cotton bud, and moving the heads a few times to get an even and thin coating on the rails. Finally wipe away any excess. http://www.lo-tech.co.uk
Sticky head mechanism I find that after some years, especially if not used, the shiny metal head-guide rail becomes dry and maybe even covered in fluff/dust ... especially at each end. (They tend not to become worn as such, as the steel is high quality and very dense on these early 80's drives). If you can very gently get the head guide rail clean and fluff free (Tweezers then a cotton bud soaked in (tape head cleaning) Isopropyl alcohol should work wonders), then leave it for 10 minutes... before you apply an extremely small amount of spindle oil (watchmakers or sewing machine oil is great). Put a little tiny drop of oil on the rail, then move the head carefully up and down the rail a few times. After doing this, if you can see any residual oil at all... then you need to wipe it off. Basically any residual trace amounts of oil under the head runner will suffice for at least another 10 years! Then before you re-install the drive, make sure that any moving parts/springs etc don't have any fluff or dust on them. Your drive will now be able to self adjust the head position accurately... as it did when it was new. The only drawback "might" be that if you have any disks that were useable/formatted whilst the disk was going out of alignment, you might find that after this procedure, they are unreadable. This can be got around by fixing one drive, then copying all your disks to that drive from the other "dirty" drive BEFORE it is cleaned/fixed in the same way. It is always good practice to also clean the edge connector of the drives before re-fitting... use either an eraser or Isopropyl alcohol. In a similar vein, Mike Rudkin has posted this advice on

Andy Key's Memotech Hardware webpage

Stiff lock handle With poor spring tension when released. Again a lubrication issue. Close the door lock, and remove the screw from the door pin actuator at the front of the drive (a single cross-head screw) and slide it back a little. Next stand the drive on end as required and apply one drop of 3-in-one oil to the door lock shaft ends, such that it runs down in to the plastic bearing. Reposition and secure the door pin actuator and open the drive lock, and then apply a little grease to the spring cam half way along the shaft on the faces that will turn against the spring. Finally operate the lock a few times to work the oil and grease in fully. http://www.lo-tech.co.uk
Dirty optos There are three opto sensors - read-only tab, disk position, and head track 0 position. All three can be cleaned with a cotton bud dipped in isopropanol that has first been compressed such that it will fit in the openings. http://www.lo-tech.co.uk
Worn drive belt The drive spindle is belt driven, rather than direct drive as used in modern disks. Given the age of the drives, the belts are likely to have stretched leading to slippage.  
     
     

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