C64

• The 6510 and the 8500 from the later boards are interchangable, you can replace one with the other.

• http://www.linusakesson.net/scene/lunatico/misc.php
• http://www.linusakesson.net/programming/poems-for-bugs/index.php
• http://www.aaronbell.com/secret-colours-of-the-commodore-64/
• https://www.metafilter.com/114704/Demoscene-The-Art-of-the-Algorithms
• https://digitalerr0r.net/2011/04/30/commodore-64-programming-6-raster-interrupts/
• https://csdb.dk/forums/?roomid=11

• Supermon Overview

• Black PSU - 5.1v/10.3v - 5.13v/10.40v
• White PSU - 5.15v/10.2v - 5.19v10.43v

• Arduino Kernel Rom
• JiffyDos DolphinDos Mod
• JaffyDos

• Remove ICs
• Heatsinks
• #11 "Zero Insertion Farce?" — Installing ZIF Sockets on a C64 Motherboard
• Sells Nordic Replays, C64 Reloaded Motherboards, SuperPLA
• EEPROMs as ROMs
• Using the USB Logic Analyzer with sigrok PulseView
• C64 Video Cables
• https://github.com/fdivitto/FabGL

Dead Drive

• https://www.lemon64.com/forum/viewtopic.php?t=64021
• https://www.youtube.com/watch?v=CDj6JEqPkzA
• C15 Capacitor

Dead C64

• this guy scopes
• Scope on the C64
• Black Screen Guide
• Another Black Screen Guide
• https://www.youtube.com/watch?v=Mn1keRFXX7I
• Test Fuse
• Test for 5 volts on chips
• check +12V on pin 13 of the VIC
• 5 volts on userport
• https://github.com/jamarju/c64_test_tools
• Commodore 64: how to repair it, step by step

• Replacement PLA, local (more expensive), Alternative, cheaper from the store
• Replacement Capacitors
• #01 "A Change of Heart" — Commodore 64 Black Screen Repair
• aphexteknol
• the 250425 board should in fact boot to the familiar blue BASIC screen just fine without U1 and/or U2. (However, with U1 gone, e.g. the keyboard obviously won't work and with U2 gone, e.g. the serial port won't work).

• Chip Data
• Datasheets

VIC-II

• [1] - £23.84 (AUD$45.19)
• Commodore 64 VIC-II MOS 8565 R2 PAL video chip 5v (*TESTED*)! WRONG CHIP. Also dodgy and more expensive...

RF Mod

• I did this RF mod mod
• Removing the RF modulator on a C64 (PAL, 1983, W. Germany 251137, Rev B)

TODO

• Black Screen. Pulses monitor/pops when turned on.
• Power supply seems ok (5.18v). Fuse replaced (I managed to blow it while poking around with the multimeter :/)
• Nothing shows up when toggling on and of rapidly (PLA check).
• Disk drive spins up when turning on.
• Load "$",8 does nothing (not sure the disk drive is working, had to replace a capacitor). Tried poke commands to make sound without success.
• Check VIC-II Vcc is 5v. pin 40 is 5v
• you're looking for the RESET line to be grounded for half a second during powerup. Pin 3 of userport. RST line goes high after half a sec (and stays high)
• No ram chips over heat. Only hotish chip is 6510
• Address lines 0-11, seem to be under 5v but not GND. Except for pin 12, 13, 14, 15 which are 5v.
• Can I use Chroma/Luma on a composite monitor (ie for just black & white image)?

PLA

• http://forum.6502.org/viewtopic.php?f=8&t=3465

Dead Monitor(s)

• https://www.lemon64.com/forum/viewtopic.php?t=28565&amp%3Bstart=30
• https://gona.mactar.hu/Commodore/monitor/Commodore_monitors_by_model_number.html
• "found that CP2 has disintegrated! It`s a paper capacitor next to the power switch that has exploded, so that needs replacing.", "the x2 cap is a common failure"

Power Switch

• https://www.youtube.com/watch?v=g2lrrXp-Zn8
• http://www.retro-commodore.eu/2014/04/12/c1084-power-switch-replacement/
• https://randommayhemstuff.blogspot.com/2016/11/finally-swapped-power-switch-on.html 1084
• https://www.wagneronline.com.au/pcb-mount/switches/electronic-components/swp583-2978/347/pd/ PCB MOUNT PUSH SWITCH $11.50
• http://www.telespares.com.au/index.php?main_page=product_info&products_id=312936 (Much cheaper, not sure if the same)
• https://www.thefuturewas8bit.com/1084switch.html (OUT OF STOCK)
• https://au.element14.com/c-k-components/ne18-2a-ee-sn-p-6amp/switch-pushbutton/dp/2435346 - Maybe this is the same
• https://www.lemon64.com/forum/viewtopic.php?p=667259&sid=d8a1ae892e1436641358a9501da82ad1

Games

https://www.youtube.com/channel/UCnhr67lnXf3ZtcKLrr9-hSA/videos

Repair

I'm trying to repair my C64. It is a PAL, ASY 250425

It black screens.

• I have tried a deadtest cart but it still blackscreens. No flashes, waited 30seconds.
• I seem to get video 'sync'. No borders. No sparkles. Just black.
• None of the chips feel particularly hot (The VIC-II's get a bit hot but afaik that's normal).
• The power supply's 5v is under 5.2v and the unregulated 9vac is around 11vac.
• The voltage regulators on the board are outputting 4.98v and 11.88v
• Removed the SID
• Removed the CIA's
• I have replaced the PLA with a PLAnkton. I also compared the output of the original with the PLAnkton and found they matched (so now I have a spare I guess)
• Replaced the VIC-II with a new one (I guess the original was fine too).
• Replaced the clock generator with a TOLB (I'm fairly sure I broke the original circuit while poking the crystal with a multimeter, chip might still be good though).
• The reset line stays low then goes high after a few secs as expected
• I am getting around 984.9 Khz clock in and out on the 6010.
• There is activity on the CPU's datapins and address lines. All of them are seen in both high and low states.
• It seems the CPU is stuck on the kernal and not loading basic.
• On the CPU _IRQ stays high. (Apparently is supposed to be 60hz if the Kernal has programmed the CPU correctly?). I have tried with the CIA's socketed and without (Someone else mentioned the CIA's generated the IRQs...).
• BA/RDY on the PLA/CPU stay high (I think the VIC-II is supposed to pull this low on badlines normally... Not sure if that is programmed via the CPU though).
• On the PLA I see CASRAM (pin17/F0) toggle on and off (it seems opposite to KERNAL which makes sense). BASIC (pin 17/F1) stays high (Maybe one brief low on power), KERNAL(P16/F2) toggling on and off continuously. CHAROM(Pin15/F3) mostly high with occasional patches of low (maybe badlines?).
• On the rom chips the KERNAL's CS signal is toggling at the CPU rate. The CHAR occasionally triggers (bad lines?). The basic stays high the entire time. With the deadtest they all stay high (which makes sense as the deadtest bypasses them).
• AEC on the 6510 toggles on/off.
• R/W on the 6510 seems to stay high (occasional very short dips, not sure it's enough to do anything).
• R/W on the 6510 seems to toggle at 984.9Khz
• CAS on the PLA toggles on/off
• Checked the traces from the RAM's to the CPU datapins. RAM's seem to show activity.
• I removed one of the RAMs and found it a nightmare to desolder (I had no problems with the 6510 and CIA). That one tested fine (surprising considering the abuse I gave it).
• Pushing the RESTORE key doesn't seem to show do on the NMI pin on the cpu with the CIA's socketed...

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

• NMI is stuck low. Pushing RESTORE does nothing.
• 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! "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" See this also... "EXROM GAME CHAREN HIRAM LORAM". Also this, another, Expansion port info.
• Go through the "SYSTEM RAM" and "SYSTEM ROM AND I/O" sections of the diagnostics cart manual.
• Multiplexer LS257
• Test Address lines... (0-7 have been seen going high and low), todo: 8-15
• Remember to look at the AEC line to see if its a vic or CPU cycle. "AEC and CAS should have good square waves"
• Also look at BA line
• "If you don't get IRQs at all then probably U15 could be broken. That would also explain the black sreen."
• Some boot information
• German stuff
• More german test points
• Manual tape control via pokes
• "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)" No 60hz...
• Check the chip select lines on the PLA.
• "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."
• "The _CAS signal on the VIC"
• Investigate that 'himem' bodge wire...
• Diagnostic guide RAM Check...
• Replace CIA and try typing poke commands again...
• 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).
• 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.
• 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%

• "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)"