Amongst the machines I am currently renovating is a Sharp MZ-2500 or Super-MZ. It is said to be the best 8bit computer made with advanced graphics capabilities, 256KB RAM, automated tape deck, floppy disk, hard disk (optional) and a Z80 running at 6MHz.

This machine not only runs MZ-80B/MZ-2000/MZ-2200 software but makes a big jump in terms of video, audio, memory and expansion for its own software. I'm looking forward to seeing if I can further upgrade it with the tranZPUter or tranZPUter SW design to upgrade the Z80 CPU to 24MHz and provide SD services accordingly.

The MZ-2500 already has colour video output with 64K Graphics VRAM, Character VRAM and a PCG with Kanji support so it makes no sense to adapt the Video Module to this machine.

After working with the MZ-2500 for the last few months, the machine is very difficult to upgrade other than using an expansion card. There is no space for a tranZPUter unless I copy Sharp's 8086 expansion for the MZ-2000 and use a 40pin fly lead and site the tranZPUter elsewhere.

I thus decided not to pursue the tranZPUter upgrade path for this machine and just get to know it so that I can add an MZ-2500 emulation into my FPGA Sharp MZ Series emulator in due course.

First stage of renovation after strip down was to attend to the plastics. The metal work is generally fine, a few scratches which are part of the machines character (a monitor no doubt once stood on the machine top) but the plastics are ghastly.

It took quite a while to remove the packing tape, it had set like super glue and after removal and full clean, the discoloration wasnt, to me, acceptable. Where the packing tape was located the machine was almost original colour and everywhere else was varying shades of yellow. Not something I would have prefered to do but a little retrobrite had to be applied to get the plastic to a uniform colour. It is still a slight yellow but uniform across the whole front bezel now. Harsher retrobriting would have brought the front bezel to original white colour but I considered this and wanted the machine to have some of it's character rather than a new out of box assembly clone.

Second stage of renovation was to attend to the power supply. I'm not a great fan of the old switch mode PSU's as they were a black art, more modern devices using control IC's are preferable. Consequently I made a conscious decision to replace bare minimum parts and test the critical capacitors.

After removal of the PSU it was fully striped down and cleaned in a bath of Isopropyl alcohol, using a paint brush and tooth brush to clear and dislodged the years of 'electronic killer' gunge! The switch and external power socket were cleaned in Isopropyl alcohol and then with contact cleaner. The metal work was washed down in Isopropyl alcohol, cleaned up and then fine rust oil rubbed all over it to prevent the onset of rust.

I then set about desoldering and checking the electrolytics, replacing any which were out of tolerance by +/- 10%.

Finally, power up and check each of the voltage lines for noise and value.

Pictures below are from the 2nd unit under renovation, I forgot to take photos of the first machine as I was so engrossed!!

All internal metal work and bottom casing were cleaned as above, ie. with Isopropyl alcohol and treated to a wipe down with rust oil to prevent degradation. The second machine being renovated is Very rusty so additional soaking in rust penetrant was necessary.

Next up was to attend to the motherboard and expansion boards and replace all tantalum and electrolytic capacitors. Tantalum had to be replaced, plenty of examples where one has gone short circuit and taken out circuitry, some of which, ie. custom VLSI IC's are not replaceable. The electrolytics where replaced as a precautionary measure as I've encountered a number on previous machines which have gone open circuit or lost their capacity, for example the audio section on an MZ-80A didnt work due to failed capacitors.

Another item which needs attention is the NiMH battery. On some machines they leak and damage the PCB often leaving the machine unserviceable. Luckily on this machine it was intact (Brown cylindrical device in bottom left corner below) so only required a replacement.

I didnt take photos of the mainboard, before/after, so below are just some mainboard photos for reference. The orange components are the tantalum bead devices.

At this stage I connected up the mainboard to the PSU and keyboard then powered on and a rush of joy was felt after seeing the 'loading error, press C..' message. Stage one was successful.

Ever forward and onward, the 3.5" floppy drives.... once serviced I can boot a game :)

Servicing of the floppy disks amounted to disassembly and clean of all the metal work as above, cleaning of the control boards in Isopropyl alchol (the main control board) and gentle wiping and cleaning with a cotton bud of the head and mechanism. I lubricated the head control mechanism then put everything back together half expecting to delve into the wonderful world of floppy head alignment or track zero sensor replacement.

Connection to the mainboard Floppy daughter card and PSU, a prepared floppy disk (using Kryoflux) and power on.... The pleasant familiar sound of a healthy floppy disk seeking and stepping and the startup screen to Xevious... all good. I tried numerous other floppies, ie. Fenix, CP/M etc and all worked fine.

Unfortunately, the second MZ-2500 machine floppy drives had succumb to rust so this will require a lot more hard work, for now something to do on a rainy day! Maybe I can get some photos as I didnt take any of the floppy drives!!

The part I had been dreading, after numerous hours working with them on the MZ-2000, the Cassette Drive.....

The cassette mechanism for the MZ-2500 is basically the same as the MZ-2000 but with stereo heads (as it can playback/record audio cassettes and telephone recordings) and more control circuitry. It comprises of 2 control boards, whereas the MZ-2000 only has 1.

As found out on the MZ-2000, the mechanism doesnt age well, the pictures below are from the second MZ-2500 I'm renovating, which externally looked better than the first, but inside was rusting and decaying.

The ringed items are the main cause for concern, they are nylon cogs and with age start to crack where they are under greatest stress.

A full strip down is essential, right down to disassembling the head and drive modules. After washing with Isopropyl alcohol the first stage is to identify cracked cogs and repair them with plastic cement. I was at one stage going to get these parts 3D printed but decided against it. Another point of issue is the pinch roller, this degenerates and becomes like tar. Luckily you can still buy pinch rollers from China, so a quick order of 13x8mm pinch roller with 6mm rubber height and 2mm rubber diameter sorts this problem out.

Once the cogs are repaired, you need to set about greasing all the friction points, this part is very necessary as any friction, no matter how small can lead to some very interesting malfunctions. The flywheel top and bottom spindles need greasing, the solenoids need a little lubrication and the motor may need a drop of lubrication oil, on the 2nd MZ-2500 this was necessary due to rust.

The belts, if they have a deformation in them (ie. not round) they need replacing. The main belt is generally fine (ie. motor to flywheel) but the two smaller belts need replacing. The tape counter belt may need replacing if it has stretched or kinked, this belt is important because the tape counter sends pulse signals to the controller so it can determine if the tape is in motion, no pulse and it will stop the motor and disengage solenoids.

Re-assembling the cassette mechanism you can manually turn the flywheel and engage each solenoid to verify its smooth action and there should be very little additional force required on the flywheel during actions such as engaging the tape heads, and force means something hasnt been lubricated. I reassembled the complete tape drive and decided to test it, rewind, ffwd, play all worked fine, in MZ-2500 mode I could even play a music cassette, just one thing didnt work and it was the most important, the IPL couldnt see or interact with the cassette drive, either to eject the tape or engage play/rew/ffwd. This was also the case on the 2nd MZ-2500 and after researching some Japanese sites, a common fault but no cure was offered. I spent an age probing the 8255 and buffer drivers but couldnt find a cause, if I manually forced a signal active then the cassette drive would respond, ie. play. I then decided it was the input signals showing the CMT status but these 'seemed' in order albeit the high/low logic levels werent definitive. In exasperation and something I was trying to avoid given the sheer number, I set about replacing all the capacitors in the CMT control boards, a long task! After re-assembly, BINGO! the drive could now be seen and the IPL would correctly engage and boot off the cassette.

These pictures are taken from the 2nd MZ-2500 I own and comparing with the first, this machine was one of the first to come off the production line. Many manual corrections on the motherboard and additions to the tape drive, such as the F2181AF-1 card including point to point wires across the control circuits show it to be a first production or pre-production unit.

Putting it all together, I was able to test the machine fully. I tried the MZ-80B mode and it worked beatifully, I tried the MZ-2000 mode and it wouldnt boot, it would 50/50 detect a tape image and when it did, after reading the tape header would stop then restart and would never complete the boot. I tried the MZ-2500 mode and BASIC M25 etc would just hang. Took a while to determine what was the issue, so one Caveat Emptor to other MZ-2500 owners who have boot problems, repair your mode selection switch. If you test the boot mode switch you will notice the resistance in the 3 settings may differ, they should all be circa 180R but some go upto 500R at least on my module. I also had a crackly speaker, this was despite washing the module in Isopropyl alcohol and using contact cleaner. It took a lot more cleaning before the switch functioned correctly and the crackling on the speaker stopped. Seems this module is more susceptible to oxidization.

Final attention was turned to the keyboard. I completely disassembled it including the key caps, cleaned it in Isopropyl alcohol (it was filthy including 2 girls hair clips) and I used contact cleaner in each individual switch tapping them multiple times to allow the contact cleaner to work. The keyboard had a bit of damage on the left side, seems it may have been put up against a radiator or similar as there are about 6 small cylindical indentations but other than this, the keyboard looks perfect and fully works. Rust oil needed to be wiped on the metal frame as rust has started to show so prevention at this early stage should see the keyboard lasting a lot longer.

The photos below show the keyboard just after disassembly.

Finally, the gallery of working shots. This machine is a joy to behold.

dtc -d0 -dd1 -wv1 -w -fsuper\ mz\ demo\ 1_d88 -e79

I bought two MZ-2500 machines thinking I could get at least one working, they both looked in good order from the auction photos but as seen, the 2nd machine is in bad condition, this is the risk of auctions where items are sold as 'junk' and expensive for this particular machine! The mainboard and PSU on the 2nd machine works but it seems that someone scavanged it as there is no expansion card frame (unless these were optional extras, as I found out was the case on MZ-80B's expansion frame recently) or expansion options. The floppy drives are in a bad state and both need work and realignment, worse case is I have to adapt more modern 3.5" drives if possible, the cassette mechanism needs a lot of work.

It was always the intention to sell one of the machines if I could get both working, the first machine is perfect and is more a collectors item, the 2nd has a working motherboard and suitable for testing and development projects but not really for sale other than 'junk'! My thinking is thus to sell the first machine for the right price, I prefer to keep it for myself but if a collector is interested then I'm willing to part with it. That being said, it is dependent on getting the 2nd machine to a useable state, if this is not achievable then I will keep the first otherwise it means buying a third MZ-2500 from Japan (when they come up for auction) and taking another risk that it will work. Watch this space as I will add the 2nd machine renovation details in due course.

UPDATE: Famous Last Words, I ended up buying 2 more MZ-2500's as the 2nd unit mentioned above was unserviceable junk! I bought 2 as there was a period when a few came up and the experience I garnered above showing some were junk I increased the possibility of ending up with a working machine by buying 2!!! Costly, you bet! Well, I lucked out, the 3rd and 4th machine, albeit not show model condition, were both serviceable. One cassette drive was not serviceable but I was fortunate that a Japanese collector I sold a board to sourced and sent me a working unit and a very nice memory expansion board, thank-you Sun Saito! A bit of hard work replacing all the capacitors, stripping the cassette decks to clean and grease, replace belts and pinch rollers etc. The hardest part was what felt like 100 capacitors on the 3 stacked levels of the cassette drive mechanism. Job done, two working machines and one came with original packaging so this one I will put up for sale and keep the 4th. In hindsight I should have kept the 1st machine, it would have cost me less and I would have a perfect example but C'est la vie!

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