I assumed that the Commodore 1581 was failing because of a bad WD1772 IC (as documented in Part I). So I ordered a WD1772 replacement + the IC socket, I developed some basic desoldering skills, watched some desoldering videos, and also got a cheap desoldering iron from Radio Shack:
So, I removed the board from the Commodore 1581 and started to desolder the IC. To my surprise the $11-buck desolder iron worked pretty well. I was able to remove all the solder from the the pins in a few minutes. The desolder iron just takes some time to reach the needed temperature, but besides that, it seems to be a great tool for occasional desoldering tasks (a hobbyist desoldering iron cost more than $250)
I removed the old WD1772 IC, solder an IC socket, installed the new WD1772 IC, assembled everything together again, plugged the Commodore 1581 into the Commodore 64, did a LOAD”$”,8 and…
and got again the FILE NOT FOUND ERROR. Sigh.😞
Time to double check everything:
- Did I solder the IC socket correctly? Did I clean the pin holes correctly?
- Is there any trace broken?
- What happens if I remove the WD1772? Will it behave the same way?
- And if the problem is not related to the WD1772, what’s the origin of this problem?
Unfortunately I didn’t have time to keep testing.
RETRO.MOE 
Great to see that you’ve tried to repait it. Sadly without success :(. Do you want to sell it or want to swap? I have a Dell XPS 10 here. Please send me an email.
thanks, but not interested.
Ok. I hope you can fix it in 2019, wish you good luck.
So what happened? Did you fix it or what?
not fixed yet
I have no idea why you would think the WD chip was faulty. #1 fault on any PCB is RAM, then ROM. I would start by swapping out the 6264 SRAM, then make sure the ROM is good. I actually reversed the 1581 PCB and made a batch of boards. You can check that on my site in the news posted 13th July 1019 here…
http://members.iinet.net.au/~lantra9jp1_nbn/gurudumps/
oops…. obviously it’s 13th July 2019 🙂
http://members.iinet.net.au/~lantra9jp1_nbn/gurudumps/
Hmm, RAM and ROM as general fault? I do not agree in this!
Its true that early DRAMs like the 4164 in C64 (first rev.) fail quite often, but then you would get a blinking code from the 1581. IF ROM fails, NOTHING would work at all, “device not present” would be all you receive…
If really all the drives were jumpered “Configured” right for usage with 1581 (and are DD-only drives with DOS 720k capacity, as HD 1.44MB drives do not work (or only with heavy modifications…), then i wd continue with the CIA 8520, as this controls also some of the drive functions! MOS8520 like its precedessors 6526 (which can NOT be used in 1581!) are known to be highly ESD (static charge) sensitive devices even not being C-MOS but NMOS-devices at all.
If there is a chance to grab such a chip from another 1581, just give a swap a try!
But do NOT buy one from ebay or other marketplaces as most of those are already dead or at least “injured”…
Then better stick to the schematics and have a look with Scope or multimeter at all the outputs, if those change states accordingly to the needed functions…
I can check your 8520 in my 1581 if you send it to me (germany).