Sharp MZ

I had a similar fault on a MZ80K. I was the flash timer is not working. The K used a 555 timer and the MZ80A uses a 556 (IC51)+ caps C39,C40 On the A the start up order is the setup clear screen print ** MONITOR SA-1510 ** test for he USER ROM/RAM at $E800 (IC43 next to the Monitor ROM) print Newlin...

Note: just to make things more interesting The MZ-80K and MZ80A ROM and RAM opcode timings are the same. But the MZ700 runs opcodes faster in RAM than ROM as the LSI chip controls the /WAIT ine of the CPU and it adds 1 extra T-cycle to the opcodes in ROM. This speeds up the tape read/write routines ...

Sounds like the horizontal synch has failed.
Check test points 13 to 21 on the video board with an oscilloscope, ( see page 40 of the MZ80K Service Manual) and compare with traces on pages 19/20.

Check that capacitors C407 c406 c503 or c504 are OK. I can remember repairing a K power supply (that kept blowing fuses ) for MH in Weymouth many years ago by replacing the blue capacitors which are part of the voltage setting circuit. I think one was short circuited but we replaced all 4. ESR is sh...

Hi I have a MZ80K with the same problem. A static random screen, the pattern is always the same on power or reset. I reproduced the fault on another MZ80K by testing a RAM checker eprom that it did not work in the faulty machine. The both MZ80K could not see the eprom,the eprom was too slow 350ns. a...

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Latest update, having problems getting the data.
The KryoFlux does not like mixed sector sizes on a track.

Access to the SUC libraries is free to SUC members and is physical media based, send tape/disk and request to the librarian. The current MZ80A librarian has no floppy disk system and is there for tape only. MZ80A disk requests were handle by Maurice Hawes who sadly he died in 2015. I have all his di...

Hi, If you check the jump vectors in the standard ROMs The JP TEMPO address at 0042h the K = FAH, A =ECH 700/800 = E5H If E5 The 800 has a 16K ROM the 700 4K ROM switch in the monitor ROM LD A($1000) LD B,A LD A,$55 LD C,A LD ($1000),A NOP LD A,($1000) CP C JR Z MZ700 must be MZ800 -----------------...

I gathered that but when I saw the different rear view images in "Sharp MZ700/8000 - EXPOSED-" by John Simpson, I thought it no good looking at the MZ700 spefications it's a MZ800. and gave a the functions of the slots, why duplicate these functions. As you said we must see the inside. I h...