Falcon - rebuilt then broken down again

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CodeKiller
Posts: 4
Joined: Mon Sep 03, 2018 9:15 pm

Falcon - rebuilt then broken down again

Post by CodeKiller »

A while back bought a broken Falcon mobo off ebay, but after a few tests and checking of logic chips in a TL866 programer (result: no tested chip worked) I concluded all the chips have been killed off :(

After some time of gathering parts and changing, finally ordered the last parts: AJAX, COMBEL, SDMA, VIDEL and a few small stuff from best electronics. Replaced them and the board worked -- for a while (albeit no sound). I use ASCO 2300 CODEC instead of the more standard CS4216 but looked fine by spec. I may overdriven the audio input from a portable mp3 player---- but normally there were no sound going through.
Then some times after it started displaying address errors, 4 bombs, lately refused to start up from diagnostic cart but still produced some image and memory test with the TOS4.04 sometimes with varied errors in the RAM. Other times just stopped after the RAM test finished and the black bar disappeared.

Now barely produces any images, mostly garbage.

What is still clear: the clock switches to 16MHz from 8MHz, the data and address buses seems ok, using some crude LA with a spartan3 devboard shows these lines doesn't stuck to any level (previously i had a broken 68030 with 2 address lines stuck to Vcc), but sometimes even if i hold the reset, the address does not change back to the 0x000000... (i'm not an 030 expert - previously even thought the reset cant come from anywhere else than u11, but reading deeper into the manual shows there is a RESET instruction to pull this pin... who knew)
Sometimes the cpu sends reset about every sec, sometime just hangs (no LDS/UDS), sometimes enters some infinite-loop.

During replacement of the chips i have delaminated a bit in one corner of the VIDEL and of course lifted some pads but checked and all seemed ok.

Any idea what to check, how to check? I pretty much run out of ideas. I don't want to buy another full set of the custom chips if not necessary...
CodeKiller
Posts: 4
Joined: Mon Sep 03, 2018 9:15 pm

Re: Falcon - rebuilt then broken down again

Post by CodeKiller »

After checking the address lines, ADDR2-3 seems dead (short to GND), ADDR4-5 is not healthy (very low resistance to GND compared to other lines, but still has signal on power on).
And its looks like another CPU kicked the bucket :( (lifting these pins of the cpu restored the resistance on the bus)
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