2021 C64 Repair-a-thon #2: 'Hmm, the mystery deepens!'

Welcome to my 2021 edition C64 repair-a-thon! In this video, I work on and fix machine #2 (of 5.)

At first I thought this would be a run-of-the-mill fix, but there turned out to be some tricky issues.
Also, I revisit machine #1 which had an additional fault that needed fixing.

Part 2 / Machine #2: This video
Part 4: Coming soon

0:00 Intro
0:46 Revisiting Machine #1 (And fixing it, again)
4:33 Machine #2 (all the way from West Germany)
36:02 Summary and outro

-- Video Links

Support the channel on Patreon:

My video on damage-free chip removal:

Jonard Tools EX-2 Chip Extractor:

Wiha Chip Lifter:
Link to desoldering video

Sven Petersen's Github (for the Diagnostic test harness files)

C64 diagnostic ROMs (including Dead Test and regular diags)

8-bit Dancy Party:

- Tools

Deoxit D5:

O-Ring Pick Set: (I use these to lift chips off boards)

Elenco Electronics LP-560 Logic Probe:

Hakko FR301 Desoldering Iron:

Rigol DS1054Z Four Channel Oscilloscope:

Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:

TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)

TS100 Soldering Iron:

EEVBlog 121GW Multimeter:

DSLogic Basic Logic Analyzer:

Magnetic Screw Holder:

Universal ZIP sockets: (clones, used on my ZIF-64 test machine)

RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)

Plato (Clone) Side Cutters: (order five)

Heat Sinks:

Little squeezy bottles: (available elsewhere too)

--- Links

My GitHub repository:

Commodore Computer Club / Vancouver, WA – Portland, OR – PDX Commodore Users Group

--- Instructional videos

My video on damage-free chip removal:

--- Music

Intro music and other tracks by:
Nathan Divino
@itsnathandivino

[adriansdigitalbasement]

In the end, I had a change of heart for those working MT RAM chips and I reinstalled them in the motherboard. At least they are socketed so it would be trivial to change a failed one in the future.

[herroncomm]

I was working on a software problem for my job tonight, and I hit a wall and gave up and came down to my couch. I started watching your video, and how you kept powering through this troublesome motherboard's issues... and was inspired to go back up and solve my problem. I did. Thanks Adrian, you saved my company's deployment.

[daveharris]

Adrian, just thought i'd mention the weirdest CPU fault we had, it took ages to resolve, but we had a C64 which would never increment the score when playing "Paper Boy" no other faults and Diagnostics passed everything... eventually tried a new CPU and all was fine. So yep i've seen a weird CPU fault as well! Keep up the good work, Dave H UK

[stephenwhite]

It is possible to determine bad RAM when you see different characters on the screen by looking up the character screen codes. In this case you could see $ in some places there should be spaces. The screen code for space is hex 20 and the screen code for $ is hex 24. So this indicates that bit 2 of the RAM is stuck high for some addresses.

[aphexteknol]

Failed 6510 CPUs are very rarely seen in NTSC machines, and yet I've seen a handful of them on the imported PAL machines I've repaired over the years. I have a theory which could explain this; as over in PAL land the use of C2N cassette drives was far more widespread which connect through the CPU. Just like the famous theory of the exposed joystick port/joystick swapping being the cause of some failed CIA chips, its possible that over the years that something similar happens to PAL CPUs when cassette drives are plugged in/unplugged. Of course a cassette drive wouldn't be plugged in as much as joysticks, but its the only reason I can think of why PAL CPUs seem to have lead a harder life than our NTSC CPUs over here when they are otherwise the same. I've actually seen the bad zero page fault on a CPU before, as when they do fail (rarely) they tend to keep mostly working but glitch out on one specific test/function. Its strange.... -aphexteknol

[onetwothreefourfivesixlemo]

This channel is one of the few things keeping me sane recently. Only recently subscribed, so still got a huge amount of content to look back through.... Thank you!

[MrSatellitehead]

You need to start a One leg in the grave bin for those chips that still have a pulse.

[joshuareynolds]

You're repairing pieces of my childhood to release into the world. That's something even I have failed to do. Love the channel:)

[Frank-Thoresen]

Congratulations with 100 000 subscribers Adrian. It confirms that you are on the right track.

[Alphonsefisheater]

Your' patience and enthusiasm for olde C64s is inspiring . So much so, that I have now bought a few olde computers and am in there solderring and desolderring to my hearts' content .

[inferno]

The dead parts bin had quite the feast on this episode

[qwertyuiop-kefs]

i know nothing about computer hardware but can't stop watching

[Laceykat]

I love your opening credits. It looks like you reposted an old VHS episode. You even have some color bleed.
Great job as usual. Keep up all the fine work you do.

[davidegalliussi]

seeing these machines working properly is a wonderful sight ... and then when it's a Commodore 64 there is empathy

[laxrrs]

Key phrase, "falsely accused chip." We must fight against chip injustice!

[nubieslayerkaka]

With working 50 HR weeks this is what helps me get thru it thank you so much for the great content!

[StofStuiver]

If i remember well, there never was a soldered RF shield on the c64's in NL/Europe. I repaired dozens at least, back in the day.
They didnt have a real metal shield to begin with; it was just flimsy cardboard with a metal layer on it with the thickness of alu wrapper for food and that connected to the expansion slots metal casing with a sort of sliding clip.

[michaelcarey]

My Commodore 64 is a made in W. Germany model. It came with all of the main chips (CPU, ROMS, CIA, SID, VIC, PLA) in sockets. Very handy as I killed more than a few CIA chips playing around with the User Port.!

[SimonZerafa]

"Dead Test Redemption" followed by "Dead Test Resurrection" as T-shirt slogans?
Keeping with an Easter theme at least 🙂
Perhaps good game titles? 😉

[jeromethiel]

The thing about diagnostic software, is to get the most out of it, you need to know how it does the tests, and how it interprets the tests. If you do not know how the test is done, you cannot trust the output. I used to have a whole suite of testing software when i was an IBM PC repair tech back in the day. And you could run several different ram test, and some would pass bad memory, and other would not. In then end, because i didn't have access to the source code of the testing software, you just learned which tests were good for detecting specific problems. For example some were really good at finding "slow" memory chips. Just because it says 250 doesn't mean it actually works at that speed. While others were very good at spotting "flakey" or intermittent bit errors.

In short, that dead test may be small enough to reverse engineer by hand, if the source code isn't available. If it is, then use that to determine why the tests are seemingly giving you bad information.