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

TonyDuell · 25th Sep 2021, 4:35 pm

You have a 'scope, I believe. I'd look for 'activity' -- square waves or pulses -- on the pins of the DRAM chips. I am guessing these are 4116-like devices (sorry, I don't have the MZ80K service manual to hand, I have an MZ80B...) in which case :

Power (check these with your multimeter):
Pin 1 : -5V
Pin 8 : +12V
Pin 9 : +5V
Pin 16 : Ground

Address inputs, there are 7 of this on pins 5,6,7,10,11,12,13. All should be showing changing logic states

Data In : pin2 and Data Out : pin 14 should also almost certainly be changing

RAS/ : pin 4 should be changing state, it would even be used for refeshing the RAM even if the CPU is not trying to access it

CAS/ : pin 15 and Write Enable : pin 3 could be high all the time if the machine is not accessing that part of memory, or if it is not writing to memory. I would certainly expect them to do something after a reset, it may be worth wiring a push-to-make switch to the reset switch 'holes' on the PCB so you can reset the machine easily.

25th Sep 2021, 4:35 pm	#129
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Sharp MZ-80K help needed on repair You have a 'scope, I believe. I'd look for 'activity' -- square waves or pulses -- on the pins of the DRAM chips. I am guessing these are 4116-like devices (sorry, I don't have the MZ80K service manual to hand, I have an MZ80B...) in which case : Power (check these with your multimeter): Pin 1 : -5V Pin 8 : +12V Pin 9 : +5V Pin 16 : Ground Address inputs, there are 7 of this on pins 5,6,7,10,11,12,13. All should be showing changing logic states Data In : pin2 and Data Out : pin 14 should also almost certainly be changing RAS/ : pin 4 should be changing state, it would even be used for refeshing the RAM even if the CPU is not trying to access it CAS/ : pin 15 and Write Enable : pin 3 could be high all the time if the machine is not accessing that part of memory, or if it is not writing to memory. I would certainly expect them to do something after a reset, it may be worth wiring a push-to-make switch to the reset switch 'holes' on the PCB so you can reset the machine easily.