Editing C64 (section)

==Checking Cartridge Port==
The system came with a weird bodge wire. One of the ground pins on the cartridge port had been cut and from the socket a wire with a probe end was connected to HIMEM pin on the 6510. I assume this is some cartridge select mod thing?. Otherwise maybe the cartridge socket is broken which would make the deadtest useless... I *might* have been told something about a broken cartridge port that when I got this system 15 years ago but I could just be imagining it.

* The D0-D7 traces connect to the ones on the CPU

I have tried using poke commands to generate sound without success. Also tried to make the disk drive do something via load with no response (but I'm not %100 sure the drive is working). Tape drive motor spins continuously when plugged in and play is pressed (but doesn't require any buttons to be pushed).

I have a multimeter with freq meter.
A 8ch logic analyser.
A logic probe pen.
I don't have another C64 to swap things with.
No Oscilloscope :(

I'm not really sure where to go from here.

===MISC===
* Addresses 0-11 are connected from CPU to ROMs.
* BA = Bus Available. Comes from the VIC, VA=1 means the VIC is using BUS.

===TODO===
* <strike>NMI is stuck low. Pushing RESTORE does nothing.</strike>
* [http://www.zimmers.net/cbmpics/cbm/c64/vic-ii.txt This shows the VIC-II taking over a bus]
* NMI high, pulled low for a short burst when restore key pushed. Seems like the address lines respond by trying to read the vector addresses.
* Investigate HIMEM! [https://www.atarimagazines.com/compute/issue32/112_1_COMMODORE_64_ARCHITECTURE.php "HIMEM control to flip out the Kernal, BASIC ROM is also removed.", "EXROM and GAME and may be changed only by plugging a cartridge into the expansion slot"] [https://www.c64-wiki.com/wiki/Bank_Switching See this also...] "EXROM 	GAME 	CHAREN 	HIRAM 	LORAM". [http://markus.brenner.de/cartridge/ Also this], [https://github.com/SukkoPera/OpenC64Cart another], [https://www.c64-wiki.com/wiki/Expansion_Port Expansion port info].
* Go through the "SYSTEM RAM" and "SYSTEM ROM AND I/O" sections of the diagnostics cart manual.
* [https://youtu.be/Znh6tyVLG-E?t=778 Multiplexer] LS257
* <strike>Test Address lines... (0-7 have been seen going high and low), todo: 8-15</strike>
* <strike>Remember to look at the AEC line to see if its a vic or CPU cycle.  "[https://www.lemon64.com/forum/viewtopic.php?t=56326&amp%3Bstart=15 AEC and CAS should have good square waves]"</strike>
* <strike>Also look at BA line</strike>
* "[https://www.lemon64.com/forum/viewtopic.php?t=63337&sid=4e7439910eac1fc27fb2bda551f34088 If you don't get IRQs at all then probably U15 could be broken. That would also explain the black sreen.]"
* [https://www.lemon64.com/forum/viewtopic.php?t=45986&start=15 Some boot information]
* [https://translate.google.com/translate?hl=en&sl=auto&tl=en&u=https%3A%2F%2Fwww.forum64.de%2Findex.php%3Fthread%2F47969-messpunkte-mit-dem-oszi-beim-c64%2F%23post628526 German stuff]
* [https://translate.google.com/translate?hl=en&sl=auto&tl=en&u=https%3A%2F%2Fwww.forum64.de%2Findex.php%3Fthread%2F41268-versorgungsspannungen-messen-messpunktbilder%2Fhttp%3A%2F%2F More german test points]
* [https://www.lemon64.com/forum/viewtopic.php?t=49548&amp%3Bstart=15 Manual tape control via pokes]
* <strike>"if the 60Hz can be found on _IRQ (pin 3), the KERNAL was able to program the CIA timer". "IRQ has a duty cycle of 98% high (2% low)", "IRQ -> generated by the CIA, but no IRQ does not automatically mean CIA bad, with no IRQ the sytem should start w/o cursor (blink)"</strike> No 60hz...
* Check the chip select lines on the PLA.
* "[https://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com&sl=auto&sp=nmt4&tl=en&u=https://www.forum64.de/index.php%3Fthread/47969-messpunkte-mit-dem-oszi-beim-c64/&xid=17259,15700021,15700186,15700190,15700256,15700259,15700262,15700265,15700271,15700283&usg=ALkJrhiPt1i08foZw42MK9kQo-9wmzVQxg verify AEC (pin 5 of the CPU) in relation to PHI0. If you don't catch a badline it looks like AEC is the same as PHI0, only slightly shifted. With a badline, AEC would be LOW all the time.]"
* "[https://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com&sl=auto&sp=nmt4&tl=en&u=https://www.forum64.de/index.php%3Fthread/66610-assy-250425-startet-nicht/&xid=17259,15700021,15700186,15700190,15700256,15700259,15700262,15700265,15700271,15700283&usg=ALkJrhjMVEWY18ZXZGvEFc7dLFWl7csdrA The _CAS signal on the VIC]"
* Investigate that 'himem' bodge wire...
* Diagnostic guide RAM Check...
* <strike>Replace CIA and try typing poke commands again...</strike>
* Remove more chips...
http://retro64.altervista.org/blog/commodore-64-repair-a-quick-guide-on-the-steps-required-to-fix-it/
* pin 21 (color clock, 17.73 MHz) and pin 22 (dot clock, 7.88MHz).
* [https://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com&sl=auto&sp=nmt4&tl=en&u=https://www.forum64.de/index.php%3Fthread/47969-messpunkte-mit-dem-oszi-beim-c64/&xid=17259,15700021,15700186,15700190,15700256,15700259,15700262,15700265,15700271,15700283&usg=ALkJrhiPt1i08foZw42MK9kQo-9wmzVQxg Test Points]
* _CS on the ROMs: The BASIC-ROM (901226-01) is not addressed in idle mode, but access can be produced simply by pressing the RETURN key
* The duty cycle of _CAS must be higher than that of _RAS for the DRAM to work.
* [https://www.lemon64.com/forum/viewtopic.php?t=46607&amp%3Bstart=15 Some signs I had that the 6510 could be stuffed was a non existent BA signal and a messed up looking RW signal.]

  Signal where?  Frequency duty cycle 
  PHI0 CPU Pin 1 985 KHz 50% 
  _IRQ CPU Pin 3 60 Hz 98% 
  _RAS VIC Pin 18 1.97 MHz 27% 
  _CAS VIC Pin 19 1.97 MHz 41% 
  Dot Clock VIC Pin 22 7.88 MHz 56% 
  Color Clock VIC Pin 21 17.73 MHz 45%

* "[https://www.lemon64.com/forum/viewtopic.php?t=65276&sid=df838812851c76508e46f113cfda2855 If you plug in a cassette tape does the motor run if you press play? If it does the computer's running, it's just something screwing up video (I had a faulty RF modulator do that to me once)]"