Search found 54 matches

by rmzalbar
Tue Feb 25, 2020 8:55 pm
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

Those half-pins on the end are a little more fragile as they are milled off there. A little contact cleaner or alcohol may help lubricate insertion/removal. If you're in the US, you can get new old stock DRAM from Unicorn Electronics. Any of the 4164 16-pin DRAM on this page will work: https://www.u...
by rmzalbar
Tue Feb 25, 2020 8:49 am
Forum: Hardware
Topic: PAL red/green color moire, not in NTSC
Replies: 51
Views: 487

Re: PAL red/green color moire, not in NTSC

After weeks of bright sun, there was none this weekend, so no bleaching possible. It's fully stripped down and I've bathed the case and keycaps, warm-air lifted and set aside the decals. Clean the keyboard frame and mainboard probably tomorrow night. This weekend I will be out of town, so perhaps I ...
by rmzalbar
Sat Feb 22, 2020 5:51 am
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

The address signals are generated by the mutiplexers and received by the RAM, so you should not expect to see anything on the DRAM pin after lifting it from the board. On the schematic, the MA-lines are the address lines, and each one runs to the same pin on each DRAM. The pins are numbered on the s...
by rmzalbar
Fri Feb 21, 2020 8:07 am
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

Each address line is connected to the same pin on all RAM chips in parallel. A problem with any chip will show up everywhere along the address line you test, so you wouldn't necessarily know which chip is bad unless you started removing them from circuit. For example, if you suspect U9, you'd clip i...
by rmzalbar
Fri Feb 21, 2020 5:09 am
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

Just did a little testing. I get 4V peaks on all address lines, your pin 9 and pin 13 should look no different than the rest, and are definitely showing a problem. Reset pulse is a little less than 1/2 second. You probably need to turn off the trigger or raises it above 5V to keep it from "freezing"...
by rmzalbar
Fri Feb 21, 2020 2:50 am
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

If the reset were the problem - not resetting long enough - then yes forcing a manual reset should allow it to boot. One bad DRAM can cause the computer not to start, so all obvious issues with the DRAM need to be solved before moving on. A pin with no signal might mean it still doesn't have a good ...
by rmzalbar
Fri Feb 21, 2020 2:12 am
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

The amplitude should be the same for all address lines. Both of those address lines are serviced by the 74LS258 multiplexer at U14, pins 4 and 7. None of the other address lines are. BTW, RESET is a 1k pullup, so you could force a reset by just by grounding pin 40 of the CPU for 1/2 second or so, bu...
by rmzalbar
Thu Feb 20, 2020 8:46 pm
Forum: Hardware
Topic: PAL red/green color moire, not in NTSC
Replies: 51
Views: 487

Re: PAL red/green color moire, not in NTSC

Yep, that's the same case. I wanted to clean it up before putting up any pictures.. this weekend
by rmzalbar
Thu Feb 20, 2020 8:43 pm
Forum: Help!
Topic: C64 With Black Screen
Replies: 21
Views: 163

Re: C64 With Black Screen

Clocks are good. The reset signal seems too short. There's a 555 timer, and the width of the reset pulse is defined by capacitor C24 and resistor R34. Looking it up, it seems that is should be about 1/2 second, shorter than I seem to remember. The square waves are fine in the first two images. What ...
by rmzalbar
Thu Feb 20, 2020 7:48 pm
Forum: Hardware
Topic: PAL red/green color moire, not in NTSC
Replies: 51
Views: 487

Re: PAL red/green color moire, not in NTSC

The C64G, is that the breadbin style one sold by ALDI supermarkets in Germany at one time? Not exactly. The C64-G is a C64-C mainboard in a white breadbin case, with a white C64C keyboard and a green LED. The label is vinyl and has a light gray theme. I like these as I prefer the breadbin case, and...