MZ-721 power supply repair

Post Reply
User avatar
tingo
Posts: 21
Joined: Wed Oct 31, 2018 9:10 pm

MZ-721 power supply repair

Post by tingo » Mon Dec 10, 2018 10:39 pm

While I was testing stuff on my MZ-721, a small pop came and then smoke started to rise. I quickly turned off the machine, just in case it is more severe than the power supply. A visual inspection shows that one of the capacitors in the psu is dead (leaking) so it is time for some repair. the tantalum and electrolytic capacitors pass a visual inspection, at least.

Luckily the mainboard looks ok.

I have the service manual, and found the "Repair PSU's" article on the original sharpmz.org.
I will be replacing the dead capacitor and any that looks like it.

Should I do more?
--
Torfinn

hlide
Posts: 209
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ-721 power supply repair

Post by hlide » Tue Dec 11, 2018 12:20 am

Is that a X2 ?

I had this issue (it is not necessary to work but I dedided to replace while I could only remove it).

https://forum.system-cfg.com/viewtopic. ... 99#p133548 (french language).

User avatar
tingo
Posts: 21
Joined: Wed Oct 31, 2018 9:10 pm

Re: MZ-721 power supply repair

Post by tingo » Tue Dec 11, 2018 1:24 pm

Not sure it is X2 (how do I know?) but it is X class, at least. The schematic only says 0.047 mikroFarad AC 250V. Here are some pictures:
C2_1.jpg
C2_2.jpg
C2_3.jpg
C2_4.jpg
--
Torfinn

User avatar
tingo
Posts: 21
Joined: Wed Oct 31, 2018 9:10 pm

Re: MZ-721 power supply repair

Post by tingo » Tue Dec 11, 2018 1:32 pm

And C1 (the other filter capacitor) has traces of leakage around it, even if it looks ok. Maybe it has been replaced in the past:
Attachments
psu_filter_defective_C2.jpg
--
Torfinn

hlide
Posts: 209
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ-721 power supply repair

Post by hlide » Tue Dec 11, 2018 8:21 pm

It's the same as mine. You have a choice: just remove it or replace it with an equivalent one.

It is not necessary as it was just here as a filter which "cleans" the frequencies interferences especially with old CRTs around (so your neighbours may watch their TV set). Nowadays, it is almost useless. It won't prevent your machine from running well.

If you want to replace it, look for .047µF (47nF) - 275V - X2 on eBay: for instance, https://www.ebay.fr/itm/MKP-250V-275V-2 ... :rk:1:pf:0.

User avatar
tingo
Posts: 21
Joined: Wed Oct 31, 2018 9:10 pm

Re: MZ-721 power supply repair

Post by tingo » Wed Dec 12, 2018 4:05 pm

Yes, I have ordered new capacitors ( I ordered some for C1 as well) on eBay already. They will get here in some weeks time, hopefully. In the mean time my MZ-700 runs unfiltered :-)
--
Torfinn

User avatar
rel2009
Posts: 5
Joined: Sun Jan 13, 2019 8:26 pm
Location: Manchester
Contact:

Re: MZ-721 power supply repair

Post by rel2009 » Tue Jan 15, 2019 12:29 pm

3 of the 4 MZ700s I have I've had to replace C2... fairly easy job.

User avatar
tingo
Posts: 21
Joined: Wed Oct 31, 2018 9:10 pm

Re: MZ-721 power supply repair

Post by tingo » Wed Jan 16, 2019 7:16 pm

Oops, I forgot - I've replaced C2 already. PSU is good as new now :-)
--
Torfinn

Post Reply