Electronics > Beginners
Troubleshooting Microprocessors
techman-001:
--- Quote from: james_s on December 28, 2019, 07:53:31 am ---I currently repair vintage arcade game boards, I've been removing chips intact for years, ever since I got a vacuum desoldering gun. I can pull a 40 pin DIP on a whim and I don't remember the last time I damaged a board.
--- End quote ---
Different circumstances.
We didn't have a vacuum de-soldering gun to share between 20 technicians who produced 90 complete commercial games a day including enclosures (stand up or sit down) 5 days a week. Spending more than 15 minutes on a board was not worth it.
These weren't vintage, they were the current tech of the day.
My point is that there are two ways to fix this old technology, the fast way with a few simple tools and lots of experience, or the *really* slow way with a workshop full of hitech gear, schematics and every possible aid.
paulca:
I found this fascinating to watch.
https://youtu.be/LnzuMJLZRdU
NivagSwerdna:
Do the simple things first...
Check PSU voltages (all of them), check for uP clock, check for Reset.
Things get complicated quite rapidly when DRAM and contention between main CPU and memory mapped video get involved.
https://www.retro-kit.co.uk/user/custom/Commodore/C64/manuals/C64C_Service_Manual.pdf
bostonman:
--- Quote ---If the address lines are not showing any activity at all (provided you've identified them correctly), that is a very bad sign.
--- End quote ---
Is it a bad sign because the failure is catastrophic or complex to find? This was a working C64 a few years ago, placed it in "storage", and now it doesn't have a display. As for the voltages, the power supply was built by me and works on two other units; it also worked on this C64 before I placed in storage. The 5V is a bit low though (I used a 2A or 3A regulator). With no load it's 5V, at power on it's 4.9xx V, and after the inductor (L5) it's 4.88V, but two other C64 units work fine with this power supply.
During power recycles, sometimes the address lines will show some activity (although I don't know if it's correct as the signals just jump around). Also, from what I can tell, the clock signals are present such as 14.3MHz and 8.18MHz (at U30 and U31 respectively).
I'm trying to avoid fast and hacking methods to fix this C64 for a few reasons: It's my original C64 and I'd like to keep it in tack without hacking the board, it was working before placing it in storage and now it doesn't work indicating (hopefully) one component has failed, and replacement chips are hard to get (I'm trying to avoid drop in replacement stuff designed within the last few years such as the PLAnkton which is a PLA replacement).
Thinking it was the PLA (U17), I unsoldered it using a hot air pencil and for whatever reason, the pin broke from the body of the IC. So now I'm avoiding the option of randomly removing ICs; and I don't have a vacuum desoldering station (just good old solder braid and the heat pencil).
atmfjstc:
OK, so the COLOR (14.3MHz) and DOT (8.18MHz) are going into the VIC-II chip. Now check whether the 1MHz clock for the CPU is being output on pin PHI0.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version