Mz700 repair project

CRG
Posts: 22
Joined: Tue Feb 05, 2019 10:11 am

Mz700 repair project

Post by CRG »

Well my mz700 finally arrived and my goodness does it need some love. The case is a bit broken on the edges and 2 keys are missing from the keyboard, namely the k and right arrow keys. Taking it apart revealed a nest of dust bunnies but other then that the computer appears in reasonable condition.

The power supply is dead with the c2 cap having blown in spectular fashion. C1 looks not far behind it so replacements will be ordered along with a new fuse.

I noticed the rom is labelled Mitsubishi? Is this usual in these machines?

Also mine is a mz-711 model that someone has added a tape drive to. Well I say that because as I understand only the 721 had a tape drive as standard. There are read and write ports on the rear. Can I simply run a line in to the read port from my laptop to load software? Do I need to flick the switch inside to change between the tape drives?

Sorry for all the questions but I'm keen to learn about this machine and get her up and running again.

Oh and would anyone happen to have a couple of spare keys?
hlide
Posts: 681
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide »

1) Mitsubishi ? yes, it is usual. Not all components are labelled SHARP.

2) PSU ? C1 and C2 are just filter caps and are not necessary for MZ-700 to work. They were used so your neighbour's RF TV was not noisy due to interference. But those caps do smell bad when they are exploded, so just remove them and replace them later if you really want to do so.

3) Every model of MZ-700 (711/721/731) have read and write ports on the rear. You just need to plug them. As for the tape switch, it is just for changing polarity if needed with your external tape recorder. There is no need for a switch to select internal/external tape recorder.
Fortunately for MZ-811 owners the polarity switch is outside the casing so it is not necessary to dismantle the computer as described below. Polarity is changed by system switch 4 at the rear of the computer.
4) Using laptop to load software? yes, you can but it is quite a pain to handle it as you may need to adjust the volume depending of the quality of the WAV file and to switch the correct polarity. Maybe someone else can advise which software to use.

Let's hope that you get her up and running again !
hlide
Posts: 681
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide »

CRG
Posts: 22
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG »

Thanks for the reply.

I just found it interesting that the rom is labelled mitsubshi as I would of thought it being the system rom would be one of the chips made by sharp but as they say you learn something new each day!

I need to measure the existing caps (physically) before ordering but in the mean time I'll remove both of them and try the power supply again. Is it worth also changing the remaining electrolytic caps on the power supply? I do not see any signs of leakage but they are going on 36 years old....

I've read through some of the documents on this site, very well detailed might I say, and with fingers cross if I can get the computer powered up I'll try to load basic or something of the sort.

My hunt for replace keys is coming up a bit short. I would be grateful of any advice anyone could give to help me in finding the parts short of buying another machine that is.
CRG
Posts: 22
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG »

So I spent some time tonight and removed the offending caps from the power supply, replaced the fuse and after reassembly and switch on I got a beep and picture on screen. Delighted would be an understatement. Next issue is the keyboard and it looks as if a fair few keys are not working along with the 2 broken ones that need replacing. I'm hoping the faulty keys just need a clean underneath and I've been thinking of 3D printing the 2 replacement keys and plungers I need to complete the job. Yes they won't be an exact match and won't have the graphics on them but its a start and should be a fair bit cheaper than trying to find a replacement keyboard.
hlide
Posts: 681
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide »

On my first MZ-700, some keys were not responsive. I had to unscrew the keyboard to access the card stock where the circuit is embedded. I clean it with alcohol and remount the keyboard: the unresponsive keys are responsive now.
CRG
Posts: 22
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG »

I'll hopefully be getting into the keyboard tomorrow and I've been speaking a 3d printing company to make me the keys and push rods I need. Would anyone else be interested in spare keyboard parts if I order a few extras?

Also I'm ordering the replacements caps for the power supply. Is c2 a 0.01uf x2 cap? Just want to be sure before ordering as my old one was completely destroyed.

Edit, never worry on the cap as I noticed on the power supply repair thread it's a 0.047. On order.
Jo Even
Site Admin
Posts: 152
Joined: Wed Jan 17, 2018 9:28 pm

Re: Mz700 repair project

Post by Jo Even »

hlide wrote: Wed Feb 13, 2019 3:56 pmI clean it with alcohol and remount the keyboard: the unresponsive keys are responsive now.
Exactly my experience with both my 700's. Clean the traces AND the carbon dot on the rubber domes with alcohol.
CRG wrote: Fri Feb 15, 2019 6:55 pm I'll hopefully be getting into the keyboard tomorrow and I've been speaking a 3d printing company to make me the keys and push rods I need.
I also have a 700 with a missing key AND I have a 3D printer. Not sure if my printer is good enough to print the plunger, but it would be an interesting experiment. I'll have a go this weekend if time allows.
CRG
Posts: 22
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG »

I haven't had a lot of time recently but spent a few hours tonight cleaning the keyboard which was unbelievably dirty and now it certainly appears that all keys are working again. I'm going to retro bright the keys and the case for my next step so don't want to fit them all again just to remove them in another few days. A few of the springs have rusted a bit but I believe if I leave then in white vinegar for a while it should solve that.

Also gave the motherboard board a really good clean as it was one of the worst I've ever seen.

Jo Even, any chance you'd consider selling the 2 keys I'm missing from your keyboard with one missing (only if it is a spare of course). I need the right arrow and K keys.

For the 2 broken plungers I noticed that the shift keys use 2 plungers each so I taken 1 from each in the hope the shift key will work normally with only the 1 plunger in place. Testing it feels ok with only 1 plunger but both springs in place and looking at the circuit layout I think it should work.


P.S. I don't know if it will interest anyone but I run a small youtube channel "Casual Retro Gamer" and I'm documenting my repair project on there (and I mean small with only 65 subs lol). I won't link the videos without permission but thought I'd mention it if anyone is interested. I'm not here to advertise that I'm here first and foremost to look help with my project and join in with the community.
hlide
Posts: 681
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide »

That's okay. Especially if you're speaking about how to repair an MZ-700, so go on.
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