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Re: Are these scope readings healthy? TT issues
Posted: 02 Mar 2022 14:31
by Steve
Ok guys! I might also check the VCC of each major chip to see if there are any voltage supply issues.
Re: Are these scope readings healthy? TT issues
Posted: 02 Mar 2022 15:01
by rubber_jonnie
Checking voltage is always good, and this is where bench PSUs are dead handy as you can match output to the original PSU and see what the current draw is, though of course you could check current with a multimeter.
How 'stock' is the machine? Is it feasible to strip any add ins out and just work on the basic TT, then add things in to see where it all goes wrong?
Re: Are these scope readings healthy? TT issues
Posted: 02 Mar 2022 17:33
by Steve
rubber_jonnie wrote: 02 Mar 2022 15:01
Checking voltage is always good, and this is where bench PSUs are dead handy as you can match output to the original PSU and see what the current draw is, though of course you could check current with a multimeter.
How 'stock' is the machine? Is it feasible to strip any add ins out and just work on the basic TT, then add things in to see where it all goes wrong?
Yes at the moment I have stripped absolutely everything and returned all SIPS to the original 10k (in sockets) I am currently investigating the MC68902 chip(s) (there are two of them) as it handles all the IRQs for SCSI and DMA. MFP/DMAC. So far I am confused as the scope does not show a constant 5v on VCC (pin 12 according to schematics but maybe this is wrong, I'll get the datasheet for the chip next)
EDIT ok yeah the TT schematic is showing the pins for the DIL package but mine is PLCC so was scoping the wrong place. Voltage is fine. Will check address lines next.