Repairing ZXkim81's C64

[@borayurt66]

Actually, seeing that it works when the SwinSID is in there is a great telltale. The Atmega88 MCU used on the SwinSID has its own internal power on reset feature. Apparently, that is also connected to its reset pin, which is connected to the reset pin of the SwinSID PCB, and in turn, connected to the C64's reset line. It was the Atmega MCU that unintentionally send the reset pulse to the CIA and made it work properly. If you tried that C64 with a real SID instead of a SwinSID, it wouldn't work. 🙂

[@JanBeta]

Thanks for sharing! That is what I would have guessed but I didn't actually check the SwinSID's behavior. Makes perfect sense! I am going to pin your comment so peeps can find the explanation. :)

[@Ramdileo_sys]

@@JanBeta *KIM statistics*.... KIM total count = 18 🤭...... average Kim count from 0:23 to 2:20 😁..... max KIM rate at 0:59 (2 KIM per second) 🤣......... just kidding Jan... nice to see this machine up and running again....... and RIP ZXKim81🥺..+..

[@MoreFunMakingIt]

Great catch on that cia reset signal! I didn't know Kim for very long, but he made a big impression on me in that short time, welcoming me warmly into the retro community. He was always positive, kind and helpful. When he fell ill and then passed the retro community lost a big heart. RIP ZXKim81

[@JanBeta]

Thanks Lee! Kim indeed was a very welcoming and helpful personality. I miss him a lot. One of the first peeps I got in touch with in the retro community and what an awesome one! Probably one of the reasons I stuck with the retro community in the first place, if I'm honest.

[@tinkrelectronic]

.So sorry to hear they passed =( Agree fully!

[@gothesouthway]

The beginning was sad sorry to hear about your friend. I hope they lived their best 8 bit life.

[@JanBeta]

He certainly had a lot of fun with his 8 bits while he was alive. :)

[@paulmichaelfreedman8334]

In a 2-bit world, that's a win!

[@madmartigan1498]

One of my C64s (240407 long board) drove me crazy for several years until one day I found out that I had soldered in a socket but one pin was bent and not connected... boards that someone messed around with can be hell. Otherwise, most of the time there is a quick and easy fix. Yesterday, I repaired a 250407 for a friend who found it in the cellar of his parents' house after 40 years. Bad switch, bad ram chip (u11) and bad cia (2). Now everything works perfectly. Even the SID!

[@JanBeta]

Yeah, boards that have been worked on previously can be extremely challenging indeed! It's much smoother sailing to work on a factory C64 with some of the usual suspects that fail frequently. Even if they often develop multiple faults over the years as in your case. Nice job, btw! Another C64 back in business is always good news. :)

[@chinesepopsongs00]

Each time i see repairs of C64 brings so many memories. I repaired many hundreds of them between 1990 and 1996. Remembered well that using a scope looking at the quality of signals i could find the problem most of the time very quickly. On days i had a lot of boards it was maybe 15 to 20 board repairs a day.

[@JanBeta]

Oh, cool! Yeah, a scope definitely makes things a lot easier in many cases. The diagnostic tools for the C64 that are available these days often suffice but especially when there is previous repairs etc nothing beats looking at the signals and tracing the fault. Thanks for sharing your memories! :)

[@Colin_Ames]

Great video, as always. I’m sorry to hear about your friend.

[@JanBeta]

Thank you! I miss Kim a lot, such a positive and generous person, hope the C64 is going to be a good memorial.

[@R.Daneel]

I have my Programmers Reference Guide right here. The TOD pin is a 50hz or 60hz INPUT pin for the interal TOD clock. There is a jumper on the board to select 50/60 aka PAL/NTSC. Don't immediately see how that jumper status gets to the 6526 - presumably Kernal at boot sets the Control Register A (CRA), bit 7 (TODIN) to 0=60, 1=50. P.S. Burn a custom ROM to change the boot screen message to a Kim memorial?

[@ddummer]

Good P.S :)

[@JanBeta]

Makes sense! Thanks for reading up on it and sharing!

[@samuraidriver4x4]

Not as easy diagnoses but easy repair. I say go for that new case as the backstory of this c64 makes it definitely worthy of one.

[@JanBeta]

It's definitely going into a nice case soon and is going to see some regular use. :)

[@KieronWray]

Thanks

[@JanBeta]

Thanks so much! :D

[@stephenvalente3296]

Glad to find another of your videos. Not sure why they're not popping up in my feed though!

[@JanBeta]

Did you "ring the bell"? Sometimes that helps with notifications but KZbin works in mysterious ways unfortunately. :/

[@stephenvalente3296]

@@JanBeta The notification setting was set to Personalised rather than All for some reason! Good to see another video there today to watch.

[@eddielegs344]

Good job again. Hahaha so that's where you got that tune from nice of you to tell us after all these years Jan. You know what I always thought was super tune even now after all these years of the game Rambo beginning song with the old SID. R.i.P Kim Gr Ed

[@JanBeta]

Thank you! The Flip & Flop tune just seemed like a perfect fit when I started the channel. I have a bit of a personal connection with the game and it was a perfect "start game" jingle. :)

[@eddielegs344]

@@JanBeta Cool

[@mirlivaturab9078]

Thanks very much, Jan. Another successfull repair. Good work.

[@JanBeta]

Thank you!

[@zxrenew5642]

A nice homage to a nice retro person.

[@JanBeta]

Thanks! Not an easy video to make for me but I hope I did Kim justice with this. I think he would have liked the overall tone to be uplifting, he was a very positive person as far as I can tell. :)

[@Neffers_UK]

ZXkim81 was indeed a really nice person. I only just got to "know" him via Twitter shortly before his passing. Just friendly talk about retro stuff in general and stuff like that. It was a short friendship, but not one to be forgotten :)

[@JanBeta]

Thanks for sharing! Kim was such a positive and generous person. I miss him a lot. :)

[@jjermar1]

Hi Jan, thanks for an interesting video. Do you know how/why exactly did the presence of the SID fix the missing reset signal? I mean the trace was still broken even with the SID in place...

[@JanBeta]

My theory is that the nano SwinSID just pushes out 5V TTL level on the RESET pin as soon as it is powered on. Which is of course not quite according to the original spec but in this case was enough to properly initialize the CIA. I didn't actually check this but it's the only reason I can think of for the weird behavior at this point.

[@giuseppelavecchia775]

Video eccellente. Jan sei il top!

[@roheinz5007]

Awesome 🤩👍🏼

[@christianlarsen1070]

This also makes a case for not recapping your c64 unless it needs it, which they rarely do. Amiga 600 is another story of course

[@JanBeta]

Yeah, I agree. Most C64s I've seen still had reasonably good caps. Probably a good idea to leave them as is in case you are not a 100% sure you can tackle the job without any damage. I do recap most of my machines after years of experience and I still sometimes make mistakes (although thankfully not very often) while desoldering.

[@chrisrobson8540]

definitely deserves a nice case and keyboard maybe with a personalised touch here and there......nice fix

[@JanBeta]

Thanks! This is definitely going in a nice case and will possibly get at least a personalized sticker or something. Haven't decided yet what to do but I'm glad I managed to fix the board. :)

[@simongreen9736]

It’s worthy of a crystal case ❤

[@JanBeta]

Maybe! I haven't quite decided yet what the "end product" is going to look like but it's definitely going to go into a nice case soon. It deserves to get some good use. :)

[@MikesArcadeMonitorRepair]

Great job!

[@JanBeta]

Thank you!

[@thebyteattic]

Hey Jan. I sent you a couple of emails but I suspect they are landing in your spambox! Great video BTW, and lovely memory of ZXKim.

[@JanBeta]

Oh, that may very well be. I'm going to check the spam folders. Did some "renovating" on my email inboxes recently so maybe I kicked you out accidentally. Sorry about that!

[@thebyteattic]

@@JanBeta No worries, happens to me a lot. If you don't find my message, let me know and I'll send it again.

[@DavePoo2]

Nice fix. But why did inserting that SID fix it temporarily?

[@JanBeta]

It seems that the microcontroller on the SwinSID issues its own reset signal on the pin when it's powered up. I pinned a comment explaining it now. I didn't actually double check but it's the only explanation that I can think of that makes any sense. :D

[@miked4377]

I feel for you and your friend zxkim81.....you do him proud mr.beta...

[@JanBeta]

Thanks! I miss Kim a lot, hope this C64 is going to be a good memorial.

[@klaus-udokloppstedt6257]

did I miss the reason why the CIA was working when a SID was installed?

[@JanBeta]

My theory is that the nano SwinSID just outputs a high TTL level on the RESET pin as soon as it is powered on. Not quite according to real SID specs but in this case enough to initialize the CIA. Didn't double check that though but that's the only thing I can think of that would explain the weird behavior.

[@bradnelson3595]

Nice fix.

[@JanBeta]

Thank you!

[@deborahberi3249]

Great Video! I have a C64 that Works ONLY without a SID Chip...maybe I should look at the Reset Pin, lol. -Mark.

[@JanBeta]

Thanks! It might be that the SID you are using is broken/shorted. I've seen a couple of C64s where a bad SID took down the whole system. Hope you are going to be able to find the issue!

[@meh3247]

Nice fix old chap! Your game choice inspired me to fire up the old emu and give Flip & Flop a go. Level one took me a while to figure out due to perspective issues and then level two... Yeahhh. Level two... Monkey. upside down. Gave up!

[@JanBeta]

Thanks! Yeah, Flip and Flop is not the easiest game at all. I got quite good at it when I played it regularly as a kid but (as showcased in this video) I can't even get through level 1 at this point. It gets even worse in later levels when there's enemies that chase you. :D

[@twocvbloke]

Sometimes giving something a good visual inspection often picks up stuff like damaged traces and the like, though that's easier said after all the diagnositcs have been done... :P

[@JanBeta]

These little breaks can be really difficult to catch visually. I mean, I was literally poking around the area for some hours without noticing anything. Measuring the trace made it clear in the end. :)

[@twocvbloke]

@@JanBeta Yeah, that's why I said it's easy to say that after it's done, I've fallen foul of broken traces that were a literal tiny crack in the trace that was virtually invisible 'til probing around and following the trace along until it was seen as a very tiny shiny glint where the metal of the trace was showing through the solder mask, they're sneaky little faults they are... :P

[@Ramdileo_sys]

*KIM statistics*.... KIM total count = 18 🤭...... average Kim count from 0:23 to 2:20 😁..... max KIM rate at 0:59 (2 KIM per second) 🤣......... just kidding Jan... nice to see this machine up and running again....... and RIP ZXKim81🥺...

[@preferredimage]

about half way through the video and I'm wondering when you tested the CIA you said it was fine was that in another board with a sid fitted as I wonder if the CIA has an odd fault in that it only works with the sid fitted but would also fail in a known good board minus its sid...?

[@preferredimage]

oh there we go. broken trace!

[@JanBeta]

I think the reason why it worked with the nano SwinSID must be that the chip issues its own "RESET" signal and just outputs 5V on the RESET pin as soon as it's powered on. Not according to original SID specs, obviously, but in this case enough to initialize the CIA. Just a theory, I didn't actually measure it yet, but it's the only reason I can think of for the strange behavior at this point.

[@CandyGramForMongo_]

The cursor is sitting in the chair! 😂

[@JanBeta]

I woke it up and it returned to its duty!

[@dougjohnson4266]

.

[@JanBeta]

Thank you!

[@wiwingmargahayu6831]

wow you must be from big city in germany sir i mean your c64

[@KieronWray]

adding comment for youtube search, c64 cursor stops flashing and keyboard unresponsive

[@JanBeta]

Oh, good idea. I shall add those to the hashtags!

[@gertsy2000]

😢

[@JanBeta]

Yeah, it's sad that Kim is gone. :/

[@MrGeekGamer]

Letter mafia flag. No thanks.

[@JanBeta]

Are you maybe a member of that other mafia? The "hating people for their plain existence" mafia? I prefer my stance and highly recommend you go educate yourself. :*

[@MrGeekGamer]

@@JanBeta I don’t hate anybody.