UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Sharp MZ-80K help needed on repair

Timbucus · 4th Sep 2021, 1:29 pm

Do you have a scope so that you can look at various waveforms as per the manual?

I would concentrate to make sure that the Z80 clock is working as a first step and then confirm that the circuit for the Video on Page 31 is working as you would expect.

A failure of the CG-ROM could also provide the effect you see along with RAM (Less likely to have failed as a static single rail but, still possible) or whatever cycles the address lines for display - but, if the address lines on IC41/42 are incrementing consistently (higher frequency the lower the address line) then you will know that the RAM is being scanned. The upper address lines (A10 down to A4) on the CG-ROM would display the static high/low values of the ASCII for the vertical line character if they are not cycling - also check that A3-A1 (Pins 6,7,8) are cycling for the character rows. If it is socketed then a small arduino code as per other threads to cycle each address line could confirm its contents is another good start.

4th Sep 2021, 1:29 pm	#4
Timbucus Octode Join Date: Mar 2019 Location: Barry, Vale of Glamorgan, Wales, UK. Posts: 1,364	Re: Sharp MZ-80K help needed on repair Do you have a scope so that you can look at various waveforms as per the manual? I would concentrate to make sure that the Z80 clock is working as a first step and then confirm that the circuit for the Video on Page 31 is working as you would expect. A failure of the CG-ROM could also provide the effect you see along with RAM (Less likely to have failed as a static single rail but, still possible) or whatever cycles the address lines for display - but, if the address lines on IC41/42 are incrementing consistently (higher frequency the lower the address line) then you will know that the RAM is being scanned. The upper address lines (A10 down to A4) on the CG-ROM would display the static high/low values of the ASCII for the vertical line character if they are not cycling - also check that A3-A1 (Pins 6,7,8) are cycling for the character rows. If it is socketed then a small arduino code as per other threads to cycle each address line could confirm its contents is another good start.