Mz700 repair project

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CRG
Posts: 5
Joined: Tue Feb 05, 2019 10:11 am

Mz700 repair project

Post by CRG » Mon Feb 11, 2019 11:57 pm

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: 205
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide » Tue Feb 12, 2019 1:01 am

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: 205
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide » Tue Feb 12, 2019 1:16 am


CRG
Posts: 5
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG » Tue Feb 12, 2019 10:40 am

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: 5
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG » Tue Feb 12, 2019 11:32 pm

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: 205
Joined: Thu Jan 25, 2018 9:31 pm

Re: Mz700 repair project

Post by hlide » Wed Feb 13, 2019 3:56 pm

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: 5
Joined: Tue Feb 05, 2019 10:11 am

Re: Mz700 repair project

Post by CRG » 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. 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.

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