v01d wrote:I don't know the hardware well (...)
Does anyone have suggestions as to what I should try next?
Arne wrote:Yes... definitely: do not try anything without proper knowledge! Or do you dare to repair your TV set?
Give it to someone capable of repairing it.
mpattonm wrote:DMA controller is common component to both ACSI and FDD and actually might be the one to blaim. But certainly, remote debugging can be a little tricky WD1772 floppy controller is another suspect, they are easy to kill and actually it could permanently pull down data lines (shared with ACSI port), if dead.
Judging from a fact you did not even consult a schematic you do not have much of the experience, so you might want to start with simpler one and do a blind swap of WD1772. They go fairly cheap on Aliexpress, or eBay sometimes so I would suggest you get a new one, rather then desoldering one from your other ST. Even nice big DIP package of WD1772 can be difficul to desolder.
mpattonm wrote:Well you can measure the impedance on each data line against ground, they should not be 0 ohms. Also you can measure them between each other, again there should be at least couple of kOhms, certainly not short. Thats as far as you can get with just multimeter.
Greenious wrote:I'd just like to add that you don't need a state of the art oscilloscope to troubleshoot these old computers.
There are cheap PC based ones to be found at aliexpress, banggood and other chinese sites, aswell as cheap older used ones.
Depending on where you live, you might also have an active computerclub or ham radio club nearby, they often have meetings where they tinker electronics and sometimes equipment you can borrow. It's also an excellent way of meeting people that knows electronics and it's a lot easier learning that way than from forums.
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