shoestring

Dropzone is definitely up there even though it has no gameplay in the attract. Sent from my iPhone using Tapatalk

Or a 50/50 mix of distilled water and isopropyl. Sent from my iPhone using Tapatalk

I use a soft toothbrush and vinegar. Spray the affected area with some vinegar then use the toothbrush to remove the electrolyte. Clean up the area with isopropyl once you're done. I've read that baking soda works as well but I've never tried it. It's very important to brush with the direction of the traces and not against them..

Good to hear you found the problem. Sent from my iPhone using Tapatalk

Yes that's right. Unplug the keyboard from the motherboard to isolate the problem. You could also try swapping the two 6526 CIA chips around to see if the problem moves. See here for symptoms. https://www.c64-wiki.com/wiki/CIA It's fairly easy to blow the CIA by touching pins on the joystick port. Always plug in and remove joysticks with the machine off.

Is your c64 socketed? Try reseating U1. Sent from my iPhone using Tapatalk

It might be ideal to try an acquire a cheap known working 600xl or 800xl that you can substitute chips to. Custom chips are somewhat difficult to troubleshoot due to their complexity. Rather than just substitute parts into a dead machine until it works, I think it's easier to substitute parts from a dead or partially dead machine into a known working machine until the fault is reproduced. It will also tell you if the faults lie somewhere else. I know this method isn't very scientific but it's quick and easy. I use an EEtools TopMAX universal programmer to test them out of circuit, they're not cheap but there may be cheaper options out there that can read 2364 and 27128 EPROMs. I dump the mask rom if it's readable and compare against known good CRCs in the list below. http://www.wudsn.com/productions/atari800/atariromchecker/help/AtariROMChecker.html

It's a great feeling to get results like these after persevering. Sent from my iPhone using Tapatalk

I've seen this a dozen times with Galaga arcade PCBs and NAMCO custom chips. Some of the older TI ICs were silver plated, the silver plate oxidises over time and peels off leaving the base metal exposed. It's also likely that the leads short out as the plate peels off. I would replace those chips.

The top yellow one is connected to the fire button. Sent from my iPhone using Tapatalk

Not homebrew , more of a hack as well. Designed for arcade games on my Supergun but now I have the ability to use it on anything with an Atari joystick port Sent from my iPhone using Tapatalk

Not entirely. In my case initial symptoms were a black screen. DRAMs were bad. Replaced with no change.( still black screen ) CPU tested bad by substitution in the 600xl doing weird stuff. After replacing symptoms change to red screen ( signs of life ) MMU tested bad by substitution ( red screen with it in the 600xl ) Everything tested good at this point except I hadn't gotten around to troubleshooting the freddie chip yet. Fixed the fault in the modulator which was causing intermittent video signal. With some help from tf_hh, we determined that freddie was showing signs of life but was still faulty. Replaced it ( not much change ) Re programmed the pld with the correct MMU code ( still red screen ) Discovered OS rom was bad, tested good initially so I must have killed it in the process of all that was done. GTIA was partially bad on one output only ( no keyboard clicks ).

RAS ( pin 33 ) and CAS ( pin 35 ) should both always pulse with your logic probe. Otherwise consider Freddie dead. See my old thread for what these signals look like under a scope. http://atariage.com/forums/topic/258601-65xe-repair-and-troubleshooting-advice/

Start off with the "troubleshooting" section in the service manual & also download a TTL logic data book. This really helped me fix my 65XE. http://blog.3b2.sk/igi/post/Sams-Computer-Facts-ATARI-130XE.aspx I use the same logic probe for checking stuff quickly but a scope is more ideal ( it's better than nothing I guess ). Also, a logic comparator or EPROM device programmer with TTL logic / RAM test will go a long way. I have an EETools TopMax which is great for checking mask roms / EPROMs , TTL logic and different types of RAM but it's quite expensive. I don't know what I'd do without it.

You're welcome. It is nice to get the Japanese perspective.

You could get 80 columns in most home computers, including the c64. Just needed extra hardware into the back of it. The BI-80 used it's own built in 6545 CRTC display chip, so it gave very good results.

A Japanese demo scener compares the Amiga to the x68000 http://6octaves.blogspot.com.au/2017/06/interview-with-japanese-demoscener.html

I read about Ray having 3 c64s on his bench destroyed because of a single black power brick before he took a sledge hammer to it It's been known for quite some time that when the voltage regulator shorts out in these, the 5v line can reach as high as 11v ( unloaded ). DRAMs are particularly vulnerable. The black 240v brick that I've across have heat dissipation issues exacerbated by our hot Aussie summers. They work fine in winter conditions but over voltage when they heat up.

Check out the c64 longplay video on YT of the game. That should give you some ideas.

2 player Spy VS Spy gave me plenty of laughs back in the day when I was a youngster.

It was not really useful as a computer. Mainly because the graphics hardware was strictly tile based ( great for games ) and didn't support a line drawing mode like the Aniga did, so it really struggled when it came to drawing windows. Based on its price, there was no way it would compete outside of Japan with the likes of the Atari ST and the Amiga. It was already cut throat. Jack really knew how to keep the Japanese out of the 8 bit market and I think that also carried on through to the 16 bit.

I'm glad I kept my c64 all these years.

Bryan is right. You may have good DC voltages but still have poor AC filtering which causes banding on the screen. A bad PS can hide many faults.

Don't forget without MOS, there is no way Commodore could have produced as many c64s as they did. Commodore had the ability to slash prices of the c64 significantly and absorb those costs [ although this would ultimately lead to their demise ] because they had their own chip production facility [ All thanks to TI ]. Money was invested into MOS to improve yields on chips by reducing flaws prior to production, this made their business more efficient.

Keep the 600xl, they are great. Now you have an excuse to upgrade the memory.