Jan Beta, 8-bit guy, Adrian Black and Noel Retrolab, all quality assurance seal in retro home computers repair and restoration, thumbs up!

You're on a row, Jan, great and instructive video! :-) That wonky signal is an example of three normal effects we may often confuse with a problem when interpreting the output of an oscilloscope: (1) the rising edge of a signal depends on the parasitic capacitance inherit to the network transmitting that signal; that is, it is design dependent. In the 80s, people had little care for this effect, because slow rise only slightly delays the point when the system recognizes a transition from logic zero to logic one. And since those computers operated at very low clock speeds anyway, this delay was often negligible. This is what you saw, I think. (2) Sometimes a bus line (particularly address lines) switches from zero to one, and back, without any periodicity (that is, without a discernible, repeating pattern), which confuses the trigger mechanism of the oscilloscope. The result is signals that seem to climb a step ladder up or down, displaying ambiguous logic values. This is often an artifact of the oscilloscope and not a problem in the circuit. Many a repair person has gone down a wild goose chase when, in fact, there is no problem at all. (3) Chips have internal switching because of the dynamic activity of their internal logic gates. This activity often leads to relatively small changes in the signal level visible from the outside, which is also synchronous with the system clock. Those can be confused with bus conflicts, and also lead people down a wild goose chase. In general, the oscilloscope is only as good as the operator's ability to interpret what it displays, and shouldn't be believed blindly! What you did (that is, to compare the signal to that of a working machine) is the way to go!

The PLA always likes to get involved in any C64 repair video.

@proCaylak

3 жыл бұрын

that darn -chinese army- chip assembly!

Best thing to watch on a Sunday afternoon 👌

@RalonsoF1

3 жыл бұрын

👍

"The things that ruin your day are often the most obvious ones" ... so true. When nothing makes sense or when the behavior is just off the charts, then we are likely to overlook the most obvious of things. The censored middle finger was priceless :)

@JanBeta

3 жыл бұрын

Thanks! Yeah, it happens a lot and can really kick your butt. I certainly learned a lesson. :D

Well done for hanging in there and working it out... a true "diy" and "right to repair" inspiration. I'm sure that others (myself included!) would have given up much sooner, thrown it away and told the owner to just get another one.... oh... wait... mmmm. well done again.

Rabbit Holes followed by giving the board the one finger salute spells frustration we have all experienced at one time or another. Last time I went down that road on a Commodore 8 bit was when two pins on one of the control ports on a 128DCR were shorted because one pin was bent. Yea had I done a full inspection of the ports I would of saved myself a lot of frustration and time. I have an old SAMS Computerfacts repair guides which have expected signals on the schematics which are helpful. When you have what you believe to be strange signals you did eventually do a comparison with a working unit which is a good practice which is not really different then swapping out IC's to test between working and non working units. Nice to see you putting the new scope to work. Now you have a behavior that you can document for future reference. if you have space around your bench you might want to put a Desktop or at least a notebook just for pulling up schematics and for documenting everything. Using Microsoft One Note is very helpful for creating your notes which can be synced to your other devices including your cell phone which is always with you so you can call up and review your notes or make new notes on the fly. I use One Note for everything at work and those notes save my behind more than you know. The other benefit for having a computer at your bench is if you ever get a microscope with a good camera you can do inspections and display points of interest on your screen and take pictures and what not but a good microscope takes up quite a bit or real-estate which is why some use those digital USB Scopes which kind of sort of work and I do have them which is better than nothing but only useful if you need a portable inspection tool. We all go down rabbit holes and once your through them they always help improve your troubleshooting skills. Never apologize for what your doing its all a learning experience both for you and those watching your videos. We all learn from the from the success and failures of others and none of us are perfect believe me I have make my fair share of mistakes which often occur when I get distracted, yea distractions for me is an on going 24-7 event so I have to do a lot of back tracking on what I was doing last before being able to move forward again.

The BSOL! I love how you used a contemporary based term to describe a retro repair success!

@bradnelson3595

2 жыл бұрын

Would make a great t-shirt.

A12..A15 are not connected to the VIC-II. To prevent them from floating during VIC-II half-cycles, resistor pack RP4 acts as pull-up resistor. This is what causes the wonky signals: The bus acts as a capacitor and the resistor pack needs more time to charge it, than the chips do with their MOSFETS.

@JanBeta

3 жыл бұрын

That makes sense. Thanks for the clarification! Obviously, the strange sloped signals drove me nuts for quite a while. Should have looked at the working C64 earlier... :D

You are my Hero. Who was "stubborner" or was it "stubbornier"? It was Mr. Beta, the Savior of C64´s. 👌 It is very Kind, that You mentioned Mr. Peters. 💚💚💚 c.u. Zui 😎

I had to laugh when you gave it the middle finger!

Shorter legs? Crazy, never heard of that. Great video, as always. As stubborn as Noels patient in the video you linked

@JanBeta

3 жыл бұрын

Noel's video actually inspired me to do another C64 repair. Never anticipated it would be as messy as his recent one though! :D

Your bad days are of interest to multitudes of us viewers. Thank you for bringing us along.

Wow, that was a long slog to a fix. It's really great to see that you have the same sorts of issues that I do, as sometimes we get the feeling that "Jan Beta or Gadget UK or Noel would have cracked this by now" but in reality you guys sometimes hit stupid snags like this and we are not alone! Great video, I often think that you learn more from making mistakes then you do when things just go right so well worth watching a lot of useful tips.

@JanBeta

3 жыл бұрын

I find it quite amusing that Noel had a similar C64 repair recently. The small things can sometimes completely ruin your day. Even if you have some experience with the system you're working on. But it's a good way to learn indeed!

I worked as an arcade game tech for 26 years and I had to laugh when you swore.... I remember the frustration of thinking for sure you found an issue only to have it make you feel like taking an axe to it when it proved you wrong... a familiar feeling lol

Enjoyed this video! Repairing old computers can be extremely frustrating at times, followed (hopefully) by the delight that you once again brought something back from the dead! Keep up the good work, Jan!

Oh, another little tip I picked up from watching arcade board repair videos - those Fujitsu logic IC's are known for going bad ! When you see them, suspect them. I've seen it happen myself repairing a few BBC Micro's at the Centre for Computing History in Cambridge, UK where I volunteer

@JanBeta

3 жыл бұрын

That is good to know indeed. Thanks!

Thanks for sharing this and including all the mistakes Jan! It's great to know it happens to everyone and for those of us learning really it's more useful to see things go wrong than to magically go right which is hardly ever a realistic experience!

I love the 425. Best picture and sound of all of the revisions imho.

@JanBeta

3 жыл бұрын

I like the 466 even better. Sturdier RAM chips, otherwise very much the same. :)

@Wikcentral

3 жыл бұрын

@@JanBeta I have stacks of spare ram chips. lol More 8kB in inventory than 32kB ;)

Thanks for persevering with this repair video. I am part way through a similar marathon. You covered methods and techniques, showed results, found revisions in the schematic. I could go on and on. Well done. A marvellous tutorial omnibus of investigation, deduction and repair. It's my goto reference work on C64's lol. Brilliant.

@JanBeta

2 жыл бұрын

Glad to hear that! Thanks for the kind words! I recommend checking out my collection of useful C64 repair resources (linked in the video description), too. :)

Well done Jan! I would have given up. It's a surprise that some chips seem to work in another machine; that would confuse any repairer. And that reset signal source coming from a different pin on a diff rev was another gotcha. Always good to have a known good machine and chips even with the expensive digital test equipment.

29:00 Whistling "Mission Impossible" made me chuckle :)

Nice to see I'm not the only one getting frustrated with a repair. Great work! Flash codes can be a rabbit hole.

@JanBeta

3 жыл бұрын

Yeah, the flash codes usually work well if it is indeed broken RAM but in all other cases they can be really misleading... :D

Those two address lines are crazy. I wonder what loads them like that.

@JanBeta

3 жыл бұрын

It really confused me!

Apparently, you didn’t hear me yelling “it’s the PLA” half way through. Lol Another great video. Thanks, Jan!!

I know a lot of people suggest right off the bat to yank out the roms and the CIAs. Granted you only had one socketed. But a number of times when I realized you were having misleading results, I was suggesting it to the screen over and over again. lol

@paulbruneau7379

3 жыл бұрын

I agree with this. Jan indicated that the ROM shouldn’t matter because it’s switched out by the dead test. But the chip can still pull down or up any data or address line, right?

Well done Jan. Another one resurrected from the dead. Stressful repair for you, but an enjoyable watch for the rest of us. Thanks for uploading 👍

A great example of the "Hunt and Peck" method of troubleshooting. Once you've replaced every component and it still doesn't work then you have become your own saboteur.

Love your repairs, wrong turns and all!

Loved it Jan! Sorry it was a tough one, but it was so great to see you try everything!

@JanBeta

3 жыл бұрын

Thanks! I certainly learned a lot from this!

I was shouting at the screen REMOVE THAT PLA AGAIN! Haha, one can get caught up in these repairs! Well done.

That wasn't an easy task but you managed it. Congratulation! Might be a satisfying feeling. The misleading slow rising signal, which seems to be wonky, could be a result of a (normal) tri-state high impedance condition. When no component drives that signal actively it goes slowly to high (or low or something between). And sometimes such a signal form indicates a real fault. Thats digital business.

Jan, I feel your pain. Been there too. :) Very happy to see another C64 saved. And as always, another great video.

Very well done Jan, thanks for showing the failures as well, that's what we learn most from.

@JanBeta

3 жыл бұрын

Thanks. I certainly always learn the most from mistakes I make. :)

Now I know what a wonky signal looks like. Great video Jan!

36:33 I felt that sigh in my soul. Great job.

@JanBeta

3 жыл бұрын

Thanks! This one sure took some emotional energy... :D

Always a journey with Jan! Thank you for all the great informative content 👊 Much love London u.k

Well... That reminded me of Noel's latest C64 video... And don't forget: If it shows a black screen, it is almost always the PLA! ;-)

@JanBeta

3 жыл бұрын

Noel's video certainly was an inspiration for making another C64 video. I just didn't think I would end up with an equally messy repair! :D And, yeah, it kind of was the PLA. But it still works fine in the other machine. That one really got me!

When you see a slow rise time like that, it's usually a sign that the bus is not being driven at all... the slow rise is often due to a pullup resistor. Sometimes this can be normal.... but typically not on an address bus! However in this case the address bus is split by muxes, because the VICII also generates addresses for the RAM. I know how you feel when you wanna give a stubborn system the middle finger all too well, i've had a few 500+'s with Varta damage just like that :)

@JanBeta

3 жыл бұрын

Ah, yes, that makes sense! It obviously really confused me to see a sloped signal like that on the address bus! :D And I feel you about the battery damage. Currently working on an A4000 with a lot of bad traces caused by the Varta. :/

That was a really exciting episode :-)

Love seeing that new Keysight DSO on the bench! It's a ton easier to read on video :D

@JanBeta

3 жыл бұрын

It is great to work with, too. I have yet to set up the network stuff that it has, I might be able to show crisp scope screen shots in the future, too. :)

@m4dizzle

3 жыл бұрын

@@JanBeta That'd be fantastic! I do have to say too that it's nice to see what you're probing and the scope's readings at the same time

Occam's Razor: "I suspect the PLA..." 48 hours later after exhaustive diagnostics and a few f-bombs..."It turns out the PLA was the problem!"

@JanBeta

3 жыл бұрын

Haha, yeah. :D

Did I somewhat enjoy? I enjoyed the video a lot! Thanks, Jan!

Every time there’s a shot in this guy videos that points out his window all I can think is ‘A tall nondescript building with minimal windows. Why does it look like he lives in a prison?’

@necro_ware

3 жыл бұрын

We call it Germany :D

You get a thumbs up for giving the C64 the bird! Great repair work. Always love watching you repair C64s

Great job. Well done for hanging in there.

Awesome job as usual Jan.

I enjoyed the Mission: Impossible theme. :)

I always enjoy these videos, even if the investigation may seem frustrating. You didn't give up, and got the best result: a c64 was saved. The middle finger made me lol :) Thanks for sharing the journey!

Great repair, great video. Congratulations one more time. The short chip legs thing was not of this world !

@JanBeta

3 жыл бұрын

Thanks! I felt stupid for not taking the short legs into account. It worked perfectly fine in my test machine! :D

Really enjoyed this one, a lot of great tips on troubleshooting a very odd problem!!

@JanBeta

3 жыл бұрын

Thanks! It was an easy problem to fix in the end. Made me feel stupid but I certainly learned a lot from this repair. :)

hahaha... 29:00 "Mischen impossible" ... when all replacements do not work.

Jan,hai dovuto tribolare su questo C64 ma hai vinto tu.sei il migliore.alla prossima amico,ciao.

What a nightmare Jan. well done for sorting it. Cheers Graham

Always love a C64 fault find video.. great work Jan..

@JanBeta

3 жыл бұрын

Thanks! It was quite the adventure this time! :D

i was guessing leaking capacitors... but short ic-legs.. never crossed my mind. Well done! i was watching it to get my time going (3dprint a key for my paper-dispenser) it just bendt it self... so.. i made a hole int the dispenser, and placed a splint.. problem fixed.

No need to apologize 😎Your videos are always great to watch 😊

@JanBeta

3 жыл бұрын

Thanks! Glad you enjoy the videos. This one was particularly messy though. :D

Never give up....Never Surrender!.....Sometimes we have to walk away to come back another day! :) Kudos Jan Beta....!

I have really enjoyed watching this.

great video, fascinating trace through diagnostic process, and like others i lol'd when you swore and when you showed it the finger :)

Thank you, great to watch!

Yeah I wonder if it would have been worth triggering on a bus control line (no idea about the C64 bus architecture - been years since I looked at the schematic). Otherwise when the bus is tristated you will get junk. Could also trigger on a bus control line and watch one of the data lines to see if the data line is stuck. I'd love to get a broken C64 to fix and play with but they are expensive here!

Wie immer: Ein super Video und ein Genuss zu schauen 👊🏼💥😊

What I've been working on the long board ones, I first check the fuse. It it's ok, it's usually the PLA (like 80% of the time), then CIAs and then RAMs. With short board ones, it's never the PLA, but usually CIA's and then the RAMs.

Thanks again Jan! :)

"Today in the lab..." I see what you did there, watching Fran too it seems :D

@JanBeta

3 жыл бұрын

That wasn't even intentional! Although I am indeed a huge Fran fan. Possibly watched too many of her videos... :D

@ojkolsrud1

3 жыл бұрын

@@JanBeta Hehe, Fran fan. I am one too!=D

@Ramdileo_sys

3 жыл бұрын

@@JanBeta aahhhh.. at 28:58 ..... due to "the music"..... I thought that "this C64 will self-destruct at 29:10" :-D ... by the way ... do you see the @Techmoan videos about the Mission: Impossible Reel to Reel pocket corder?? >> kzread.info/dash/bejne/aHiCo899iczbZs4.html

@hansoak3664

3 жыл бұрын

@@JanBeta There is no such thing as too many Fran videos. :)

Thanks for the exciting thriller. Murphy gets us every time ... :) Nevertheless: the patient is alive!

Very helpful and informative video for me.

Jan has the patience of a saint !!

Jan, where did you get this nice IC extraction tool? Can you recommend it?

@Doug_in_NC

3 жыл бұрын

In the text he gives a link to all of the equipment he uses. The IC extraction tool he links to is available on Amazon - in the US it’s a bit under $25.

@Torbjorn.Lindgren

3 жыл бұрын

The silver one at 9:45? - I'm guessing it's a Jonard EX-2 (24-40 pin chip extraction tool). It's not the cheapest tool and the usual suspects (like AliExpress and eBay) have much cheaper all-plastic variants going by the name GJ-3 (16-22 pin) and GJ-6 (24-40 pin), search for "Chip Extractor GJ-6" (or GJ-3). For casual use the plastic ones are fine and has a variant for smaller chips that Jonard doesn't make (it's *less* useful for smaller chips but it's still nice to have), I expect that Jan use his enough for it to make sense to go with the high-quality option. At 17:56 we see the standard "flat" extractor lying on the desk (it's used shortly afterwards), it's the one with yellow handle (green and blue are also common), this is usually the first one everyone gets because it's usable in so many situations even if you can get by without one. The second extractor people get is usually a PLCC extractor because PLCC's are *hard* to get out without damage if you don't have one.

@JanBeta

3 жыл бұрын

What Torbjorn says. It's a Jonard EX-2, I can definitely recommend. Makes things a lot easier and doesn't bend any pins etc during extraction.

@radio655

3 жыл бұрын

@@JanBeta Excellent, thanks! Amazon DE is sold out on it currently so I hope it is back soon.

Hi Jan, really enjoyed it, it’s sooo annoying getting trolled by a fault you accidentally caused yourself. All’s fine in the end :) have subscribed!

@JanBeta

3 жыл бұрын

Thanks Pete! Yeah, sometimes these faults can drive you to the completely wrong track. Glad I managed to fix this one in the end. :D

Since this case already have 2 holes on it, how about putting 2 switches on it? One to switch kernels and other to switch between PAL and NTSC?

Spit my coffee all over my laptop... lol (29:28)

A good journey and happy ending, that's why we watch. LOL at the censorship bleep and blurred finger!

Wow this one was a real slog for you..... glad you got it fixed in the end

@JanBeta

3 жыл бұрын

It was driving me nuts! :D

Grande, legendary Jan Beta! 👍👍👍

Great video as always!!

@JanBeta

3 жыл бұрын

Thank you! :D

Whew... that made me tired just watching! You have the patience of Job, sir! Well done! :)

I love it, that even with your experience you can get to the wrong slope of analysis! Just fixed up a my first dead c64 from ebay, somehow I love fixing things now...damn..bought ebay empty with electric utils and stuff

Great video, looks a lot like my efforts, with same frustrations. Maybe it would be helpful if you did a series in which you scope every chip ,one at a time, on your functional computers. This way he people who do not have a working 64 to aid in our troubleshooting , could benefit from seeing what the proper waveforms should look like. I have a scope, but I’m not sure how the waveforms from each component should behave in a machine that is not sick. That old make my scope readings meaningful. Thanks again!!

@JanBeta

3 жыл бұрын

I remember seeing a guide on some C64 forum that had osilloscope readings but I can't find it now. :/

Was great watching this and the Atari ST renovation

What would be great is to have the scope graphs of a working one saved, maybe in a program or database.

How are you connecting the proprietary video and audio output to the LCD monitor? Converter to VGA, HDMI?

@JanBeta

3 жыл бұрын

I use a Flylink SCART to HDMI upscaler box for testing. It‘s good enough for testing purposes but it introduces a lot of lag. For gaming I use a RetroTink2X.

@DM-ei6oo

3 жыл бұрын

@@JanBeta thanks Jan. I repair stuff and you did great. It all seemed like bad rams and the PLA. That new FPGA PLA replaced seems to have a design flaw. You might want to contact the designer. I wonder if your other replacements have a problem too. C64 is where I really learned programming and it has great arcade level games.

You have the patience of a saint jan, well done chap. :)

Tip for quick-testing DRAM: If you suspect one chip is bad, you can piggyback a known good chip right on top of it. Bad DRAM usually don't drive its output, so the known good chip which is tucked on top takes precedence.

@JanBeta

3 жыл бұрын

Yes, I use that method frequently.

well done / Gut gemacht! Danke Jan

You bring Another C64 back to Life!! Great👍👌

@JanBeta

3 жыл бұрын

Thanks! It was quite a mess but always good to have another C64 back in business. :)

@ralfr.5974

3 жыл бұрын

@@JanBeta Great Job Jan!! Thumbs Up!!💻👍👍👍

Points for effort and not giving up.

@Jan Beta is the your dead test cartridge modified or stock? I have a borked machine with an overworked motherboard .. I'm thinking I want to replace it with a SixtyClone and extra debugging is always a good thing.

muchas gracias Jan por tan ilustrativo vídeo aprendo mucho con ellos buen trabajo. Podías hacer un vídeo de como se construye un FE3 para el vic 20?

Hi Jan! Thanks for the exciting content. Do you know what the diodes left of 7406 IC are for? I repaired one C64 a year ago and it had such diodes there as well. They looked pretty much self made and I removed them, but I'm still curious why they were there at all. The repaired C64 works at least like charm until today without that diodes.

@danielmantione

3 жыл бұрын

These diodes protect the lines of the serial bus. Excess voltage on these lines is directed to VCC, where it cannot do much harm. With these diodes you are much less likely to destroy a CIA a static discharge of you touch the signal lines on the bus. They were clearly not part of the original plan, but warranty claims may have made Commodore to add them.

@necro_ware

3 жыл бұрын

@@danielmantione I see, thank you very much.

Awesome video, I enjoyed the process and was really surprised that the address signal was normal, that looked terrible (Sawtooth binary anyone).

Great video, where can i get sockets pack for all main chips CPU, PLA, SID,...

we always love yours video

From mistakes you learn the most.. and in the end a working c64.. bravo again Jan...is it possible to check if the short pins make or don't make contact on the board?

@JanBeta

3 жыл бұрын

Thanks! You could check continuity with the board of course. I didn't think of that because I just assumed the PLA would work after testing it in the other board and didn't look into it any further. Lesson learned for sure! :D

Great video 🙂👍

Misled by readings from the oscilloscope - and by way too short pins. Wow ! Aber jetzt haste ja (fast) alles auf dem Board gesockelt :)

29:30 I think a lot of us have been there giving the middle finger at stubborn c64 repair! 😁 Can you please comment what was beeped out on 33:28?!😄

@JanBeta

3 жыл бұрын

No comment! ;)

Testing the logic chips in a TL886 like Noel may be a good plan.

@JanBeta

3 жыл бұрын

Yes, definitely! I was about to do it in this repair but I figured out that the ICs were okay before I even got the TL866 out... :D

Mhm, Uwe Peters. Der Name hat direkt mal unzählige Erinnerungen zurückgerufen aus alten Commodore Listing Zeitschriften in den er immer fleißig inseriert hatte.