nama-chari
Chattie   Posts: 30 Registered: 3/12/2008 Status: Offline
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posted on 28/6/2009 at 10:54 |
I have spent some time repairing my MZ80k motherboard, and removing a crazy mess of wires that that someone had hacked. After a couple of months of on and off testing I finally had the MZ80k up and running. It's a great feeling when you repair something this old, and finally see it spring to life.
Unfortunately I can not load anything from tape drive. The tape plays, and seems to function perfectly, except I never get any load message of any kind.
I have pulled the cassette area apart and I am testing the cassette PCB with a multimeter, and a Logic probe (I have a feeling that the probe is not useful in this circuit though).
However I was wondering if anyone would be able to give me some pointers. I've toiled over this machine too long to give up now.
Thanks in advance.
Philip
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Jonas
Talker  Posts: 19 Registered: 15/5/2006 Status: Offline
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posted on 4/7/2009 at 21:02 |
Have you got the service manual for MZ-80K?
The manual contains a cassette tape recorder section with a trouble shooting chart, info about waveforms, info about azimuth adjustment and head cleaning, wiring diagrams of cassette section and perhaps more useful information.
Best regards and good luck!
Jonas
Download the service manual from
http://www.sharpmz.org/mz-80k/download/sm80k.pdf />
____________________
Those were the days!
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Yowl
Moderator  Posts: 54 Registered: 31/8/2004 Status: Offline
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posted on 13/10/2009 at 10:17 |
Has there been any development on this?
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nama-chari
Chattie Posts: 30 Registered: 3/12/2008 Status: Offline
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posted on 20/12/2009 at 13:42 |
Unfortunately no. I have not been able to fix the cassette deck.
I actually replaced the cassette head with another one and it worked perfectly for about a week. Then it died again..same as before. I wish I knew what the problem was. I've looked through that the trouble shooting guide, and played a lot with the azimuth setting, but the best I could get was a checksum error (and very rarely at that). Usually I get nothing. Getting a checksum error actually gave me a glimmer of hope in that there was actually something being read and getting through, but alas, i can't get anything to load. I've tried about a 50 times now with different azimuth settings.
Any advice would be greatly appreciated. Actually I'm now looking for anyone with a spare cassette unit that they dont need.
Phil
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sharpmzorg
Moderator  Posts: 46 Registered: 28/3/2004 Status: Offline
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posted on 7/1/2010 at 20:00 |
quote:
Unfortunately no. I have not been able to fix the cassette deck.
I actually replaced the cassette head with another one and it worked perfectly for about a week. Then it died again..same as before. I wish I knew what the problem was. I've looked through that the trouble shooting guide, and played a lot with the azimuth setting, but the best I could get was a checksum error (and very rarely at that). Usually I get nothing. Getting a checksum error actually gave me a glimmer of hope in that there was actually something being read and getting through, but alas, i can't get anything to load. I've tried about a 50 times now with different azimuth settings.
Any advice would be greatly appreciated. Actually I'm now looking for anyone with a spare cassette unit that they dont need.
Phil
Hi Phil,
there are a lot of possibilities which can arise over the years., one of them is this (found in wiki):
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The heads and other metallic components in the tape path (such as spindles and capstans) may become magnetised with use, and require degaussing.
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This may be the reason why you get checksum errors?
The PB head itself can be the problem. It can be worn out by the usage over years. May be, its metallic surface is deformed and not smoothly? The head has a very narrow gap (vertical slit), it should be very very thin...
If you want to calibrate the azimuth exactly you need a scope and a 3 kc signal on a tape which you can provide by a sign wave generator and a good audio cassette deck (mono signal). Next check the waves shown on page 24 and find the relating test pins on page 42 of the Service Manual.
The following is for the TRS-80, but it makes no different, I think.
http://www.trs-80.org/cassette-gazette-page-3/
Good luck!
Karl-Heinz
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sharpmzorg
Moderator Posts: 46 Registered: 28/3/2004 Status: Offline
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posted on 8/1/2010 at 18:21 |
quote:
I have spent some time repairing my MZ80k motherboard, and removing a crazy mess of wires that that someone had hacked.
Like this?:
http://web.mac.com/lord_philip/other_computers/Sharp_MZ80k.html#1 />
I also got a 80k with a similar wiring. As I can remeber, the tape recorder was changed to get a double speed or a double density, sorry, cannot exactly remember on this. Further things were done by this. I have to get the schematic diagram of it. All mods were done by a german radio amateur (ham).
I have all my MZ-stuff in Austria, coz of not having room for it this time. Next week I'm in Austria and I'll take a look for this.
Regards
Karl-Heinz
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sharpmzorg
Moderator Posts: 46 Registered: 28/3/2004 Status: Offline
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posted on 10/1/2010 at 09:17 |
I've found an unpublished article for this, which I started in 2004 but I didn't finish it. It shows the mods on my MZ-80k which enabled it for CP/M support.
My one is modified for 80 characters and can be switched from 2 MHz to 4 MHz.
I've put this article now on my site. See the article for this at my site:
http://sharpmz.org/mz-80k/4mhz_upgrade_01.htm
May be, you have a similar mod and this would help you. If not, it may help others with the same mod or others who want to enable the 80k for CP/M support.
Bernd Krueger-Knauber / Germany, well known to all of us by his fine MZ-700 emulator, and btw, he is an excellent hardware developer too, supported me to crack all the mods inbuild in my 80k.
There is one PCB which was made by a company called "Epis" (see the attached and downloadable ZIP files in my new article). They removed the labels on the ICs, so that it was a bit hard for Bernd (and me too) to find out the type of these ICs. But, the job was well done by Bernd ;-)
Bernd also created new PCBs for all mods by Eagle, coz some of the original ones are on a grid board. This will enable those who want to mod their 80k for CP/M support.
If I'm right, there is also a mod available for this from the SUC. To this read:
http://sharpmz.org/mz-80k/sscpm80k01.htm and
http://sharpmz.org/mz-80k/mz80hardware01.htm
Karl-Heinz
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nama-chari
Chattie Posts: 30 Registered: 3/12/2008 Status: Offline
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posted on 10/1/2010 at 12:56 |
thank you for gathering that 2-4mhz mod info, but I'm not to sure if that is what min was as the IC's are not the same. The only one that is the same is the 74LS00, the other two are different. I also actually had my cassette deck working for about a week AFTER removing the hack, but then it stopped, and I couldn't seem to do anything to get it working. I even get a degaussing tape, which didn't seem to have any effect at all :-(
As for the azmuth. I don't have the testing tape or a scope, so I have slowly adjusted it through it's entire range of motion, testing/loading as I go. I couldn't seem to get it to work. As I have mentioned previously, the thing that gives me a glimmer of hope is that occasionally I do get checksum errors.
Thanks again
Phil
P.S. The 80 column hack looks cool to. I may actually try building that one day!!!!
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