Commodore 64 Repair (Garbled Screen) ASSY 250407
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- Опубліковано 27 чер 2017
- I'm troubleshooting and repairing a Commodore 64 breadbin that has a garbled video output with wrong characters and two blinking cursors.
The (brilliant) Pictorial C64 Fault Guide is here: derbian.webs.com/c64diag/
Ray Carlsen's troubleshooting and repair guides are here: personalpages.tds.net/~rcarlse...
I'm using SDBrowse as the C64 filebrowser near the end of the video: csdb.dk/release/?id=152470
You can get the .bin files for various C64 diagnostics cartridges from World of Jani (in case you want to make your own or try in an emulator): blog.worldofjani.com/?p=164
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Thanks! - Наука та технологія
Nice video, and thanks for mentioning my diagnostic guide. The site isn't a "golden solution" that pinpoints every C64 problem, but can be greatly helpful in some cases, especially when used in conjunction with other sites and information at hand. This case has now been added to the site as a U14 fault.
+DerbianGames Thanks! And thanks for maintaining your brilliant site. It really is a great addition to other troubleshooting guides and obviously worked very well (and quickly) for me in this case. :)
This video saved me... was exactly the problem I had with my C64 board. It started as a memory chip failing board, but after all the memory chips were replaced, both CIA chips turned out to also be bad. After replacing those, mysteriously the screen would sometimes get garbled, but still run the diags (you could hear the SID test). Perplexed by this, I checked everything, replaced the PLA, checked the VIC-II, nothing seemed to help. I set it aside, frustrated, and went on a trip with my wife. Days later I came back, taking a fresh look, thinking it's time to start replacing logic chips. Then I watched your video and it seemed to be very similar problem I was having, though my screen didn't look same as yours. Turns out it was U14 74LS258. I have a chip tester from Evie (Backbit), and after desoldering U14 I tested it (and it passed), but I decided to still try replacing it. It seemed to be a very marginal failure, so could be a false pass. The replacement works wonderfully, harvested from a donor board (because I don't have another 74LS258 lying around). So... huge THANK YOU for this video!
Hey, that's awesome! Glad that my video helped another C64 to come back alive! :D The intermittent or marginal faults are always the most difficult to figure out. Nice work!
Always good to see a C64 come back to life - especially if it's a component that's still made like the 74LS258!
Yes, I'm going to order some of those for future repairs. The MOS equivalents used in some C64s seem to die very frequently.
@@JanBeta Can't you do a piggyback instead of desoldering?
@@ivanbiasutti4567 If its a logic chip I guess that wouldn't work - if the broken one says 1 on a pin and the other says 0, you have a 1, right - so its wrong. That's my thinking anyway, I don't know anything about this really :)
I just repaired my C64 replacing the MOS 7709! Thank You for your video!
Awesome! Great find on that pictoral faults site! Very useful!
Thanks. I stumbled across the site a while back and thought it was a neat idea. It's the first repair I actually used it. Worked very well, obviously. Also contributed some screenshots already. ;)
Thank you for this video, and all the other useful links! Helped me isolate the fault with my unit - it was the VIC. God bless you!
Awesome vid. Had some similar problems with my c64 a few years ago. At the time there weren't that many videos like this that were in HD or in English, so I did the best I could to diagnose it with some diagrams I found on the net. I ended up ordering a ram kit thinking that would be an easy fix, but that didn't help. I was pretty busy back then and didn't have lot of time to really mess with it, so I just threw everything in a cardboard box in my basement with the hopes that in the future, technological advances would make it easier to diagnose and repair it. It looks like that time has arrived! I can't wait to get home tonight and pull it out of storage and see if I can get it working again with the help of your vids. Thanks for posting these!!!!
Thanks for this comment! That's what I do these videos for. Hope you can get your C64 fixed. If I can be of any help along the way, feel free to ask. :)
Another great video. In my case, the screen was full of the "@" sign instead. Turned to be a problem with 7805 which fed 2,15 instead of 4,97 volts. Thanks and keep up the great work!
Jan, thanks for this. I had the same fault. Put in a new chip and socket but still had same fault. Went round and round for months. This video and the pictorial guide kept bringing me back to u14. Turns out the new socket I put in was bad.
I have a similar problem with a board I am working on, where it has two cursors and displays some of the keys I press correctly, while others will display the wrong letter or number. I also looked at the pictorial and came to the same conclusion that you did. However I am now just waiting for some 74LS258s to arrive. I appreciate the time and effort you have put into all of your videos.
Thank you
As usual, a rockstar repair. My first thought was the PLA, but you threw me a curve ball when you showed that everything seemed to be functioning normally under all the screen garble. The Pictorial Fault Guide is a great reference tool; I have used it quite a bit myself. And deducing the MOS7709 as the culprit was brilliant. I've made notes for my own reference. I learned a lot -- thanks professor! ;)
Haha, thanks! It was pretty easy to find the fault once I read about the doubled cursor in the Pictorial Fault Guide. That plus the fact that the MOS chips fail frequently made it clear to me that it had to be that chip. :)
Love your video's and of the same view that we should repair and keep these old computers going and actively USE them. Emulators are no substitute for the real thing, my C64 is cabled up right next to my main computer and is used as often as time permits between work and family time constraints.
Thank you! Same here. The C64 is the one that is (semi) permanently set up and gets the most use these days. Sometimes exchanged with an Amiga though. ;)
Good repair! And thanks for adding the C64 fault guide!
Thanks! The fault guide really deserves a wider audience. It's the first time I actually used it for troubleshooting after finding it but it worked very well indeed. :)
Hahaha that's amazing. I knew Ray's site, but this other site is surely helpful. One of my suspects was the character generator rom. But the double cursor was another issue. Well done Jan.
+The Highlander The character ROM I ruled out pretty quickly because it usually results in characters not being displayed correctly. They all were correct in this case, just the wrong characters so I looked for other faults first.
Great save! It's nice to watch you work. Useful links are now in bookmarks. :)
Thanks! Also nice that you like the links. I always try to spread the word about useful and nice stuff I come across. :)
Great video, liked it 🙂 just wondering, which desoldering tool do you use? Looks pretty handy.
+Diego Budavari Thanks! It's a ZD 915. I made a little review video about the desoldering station when I first got it here: ua-cam.com/video/EQEx7Cezz9o/v-deo.html
Hello! When running the 586220 I get a blank screen when it tries to run the ram test. No flashing telling me what could be wrong, just a static picture. The 781220 completes just fine and can run continously. If I start the C64 without the dead test cartridge it says 14528 Basic bytes free and a blinking cursor.
If you know what could be the cause of this, I would be very happy for some information. :)
I really like your videos. Would be nice to see some more C64 repair videos.
Hallo Jan,
sehr hilfreiches Video. Kann man die beiden Cartidges für Dead Test und für die Diagnostics eigentlich fertig konfiguriert kaufen? Ich habe leider keinen Programmer...
Vielen Dank! Es gab sogar mal ein 2-in-1 Modul bei eBay. Ich kann das leider gerade nur aus Amerika finden... "Dual Diagnostic" heißt das Teil. Ansonsten gibt es die häufig aus Großbritannien. Irgendwann in der Zukunft werde ich vielleicht auch mal ein paar basteln und verkaufen, aber momentan fehlt mir leider die Zeit für solche Unternehmungen.
Jan Beta vielen Dank für die schnelle Antwort. Ich denke, deine Follower würden das Angebot gerne annehmen! Ich jedenfalls hätte sofort eines bei dir gekauft :)
Ich freue mich auf viele weitere Videos von dir!
Great video, my C128 has the same fault in 128 & 64 mode wrong characters & double cursor, so U14 is the one I'll check first. 👍
Glad to help! I don't have a C128 to double check but I would guess that the numbering (silk screen) on the board will be slightly different. Make sure to find the equivalent of the C64's U14. (It most likely still is a MOS 7709 or a 74LS258.)
Did you take or compare any of the measurements coming off the U14?
Great Job!! What is your desoldering station? Looks really nice and easy to use! I am using a simple one with hot air but really hard to do a decent job.
+pincopallino Thanks! It's a ZD-915 (sold under different brand names). I made a video about the station a while back: ua-cam.com/video/EQEx7Cezz9o/v-deo.html
Jan Beta many Thanks for the station reference:-) I am definitely taking one of these for my future works. !
Also, what file browser are you using on your SD2IEC? I've never seen the one you are using before. (EDIT: Duh. I should read the description first.)
Haha, yeah. I linked it in because I knew somebody would ask. It is pretty good but it's a bit fiddly to work with due to strange keyboard commands and stuff (there's a list of commands in the CSDB comments also).
Do you know if there is a pictorial fault guide for the VIC 20 ???
I'm not aware of such a guide. I guess it would make less sense than for the C64 as the VIC's most common failure mode is a blank screen.
Hi, I have a problem that the characters look twisted and look torn. It looks like strips of pixels shifted right and left. I am plynning to replace the modulator anyways. I didn't Test the s video output. I am also planning on installing a lumafix64 against thd banding. Does anyone have any guesses or directions where to look?
Hah, I didn't know about that pictoral site. Thanks! :D
Hi, I just purchased a second hand C64 & when using the diagnostic cartridge it shows a bad interrupt but everything else seems normal. Is this because I don't have test harness connected or is it because my version of the test cartridge is 586220 only and not the ++ version you have?
That may very well be because of the missing harness. The Diagnostics show some errors without that connected. The ++ version only has some minor changes (at least afaik) compared to the original. It adds the ability to detect some more Kernal ROMs but not much else is different.
Tell ya honestly those de soldering stations are a must have for sure. The link for the Video Display Troubleshooting is a nice addition to troubleshooting issues. You mentioned the DPDT Rocker Switch and I just got in a 1581 that had a faulty switch that I removed and it was corroded so I have to take some measurements on it because DIGI KEY has some that are basically drop in replacements but are a bit too tall and narrow so for now I just added jumpers to allow me to test the drive. I also have a Rocker Switch on a Plus 4 that I got functioning but its a bit on the stiff side so it needs to be replaced as well. I don't even know why I even bother with the Plus 4 when the chips if you can find them cost more than the unit is actually worth, but its in my collection so I have to bother with it. I have a C64 where the dead test cartridge did not display and in testing the board out the issue came to U15 74LS139, U17 PLA and or U19 VIC-II. I put in a new PLA and got the video back but the characters on the initial display are not pretty. I swapped out the VIC-II with no change but the DEAD TEST Cartridge now displays perfectly regardless of which VIC-II chip I put in. I had to order the 74LS139 so I will add the socket tomorrow and at the same time I will check my work on the traces to the socket I put in for the PLA just to make certain I did not over look anything but the visual inspection of the solder joints looks good but you never know until you verify.
Couldn't live without the desoldering station for sure. ;)
How's the C64 repair coming along? All traces intact? I just repaired another breadbin that had a faulty rocker switch and one of the MOS logic chips was bad, too. Works like a charm now. I managed to lift a pad on the RAM but put a wire to repair it.
Nice work (as far as I can tell) on your hardware! The Plus4 is kind of a lovely machine, too although it has its weaknesses of course.
Solder Traces tested well. I am waiting for the U15 74LS139 Chip Order to arrive, After which I can resume troubleshooting my issue if it does not resolve the issue. Even the J-PLA I am trying out which resolved the Black Screen issue could in part still be an issue so I have another MOS PLA coming in. I may also opt to socket the entire C64 Breadbin and use it for testing suspect chips from other units in the future.
Yeah, especially the older board revs can be very picky when it comes to the right PLA. Socketing one C64 board completely is something I always wanted to do, too but didn't get around to doing it yet. I have one that at least has everything except for RAM and logic socketed so I can test some of the more expensive chips.
I have the C64 working the problem was with the PLA and the Character ROM. I have a J-PLA in there now and its working well. While I have the Character ROM for the C64 on order I decided to try the ROM from a C128 (315079-01) which worked perfectly but once the C64 ROM comes in I will swap it out just incase its not 100% compatible. I don't play games so I really don't have much to test it with unlike years ago when I had boxes fully of software for the C64 and 128 that I either gave away or sold off. (Pout). I did socket the CIA's, ROM's, 6210, a couple Logic Chips, Color RAM and may just socket the rest of the thing since its still on my bench before I put it back in the case. I need to get it off my bench so I can finish up working on a 128D DCR and a couple other small things then I can focus on the stuff I took home from work to repair.
I just bought my first Commodore the other day and the screen (except border) is filled garbage, it just has a checkers pattern and im hoping I found the problem, U2 6526 CIA Chip, if im wrong plz let me know
Well I thought for sure that my issue might be resolved by replacing U14 as I was getting the same double cursor and some misprinted characters. However when I tried piggy backing the 74LS258 (U14) it did not make any difference at all. So, I started comparing measurements to a working machine, and all the U14 measurements looked the same.
So, I took another look at the C64 Fault Pictorial website and at the fist fault comments. In the NOTE: It clearly stated that this problem could also be caused by a bad VIC chip. So, I swapped out the VIC and Wa-lah !!!
Of course now I have a bunch of 74LS258s and an assortment of 4164 RAM chips laying around, but I like having spare chips around for when I need them.
Great video Jan! Keep up the good work :)
Thanks! I'll do my best. More C64 videos coming soon. :)
Excellent video ! Very informative. Thank you very much for sharing these valuable infos.
+Zarchos Thanks! Hope it helps someone repairing their C64s. :)
Jan Beta Indeed it should ! Now buying some malfunctioning C64s on Ebay won't scare me anymore.
+Zarchos Nice! It's really rewarding to fix these glorious machines. :)
Nice work
22:10 my fav :-D
Great work mate.
Thanks mate! :D
Good tip :) Love a bit of Buggy Boy :) Got any good tips on making the most out of SD2IEC.. I know how to use it, I noticed you have it set up differently.. Sometimes I have issues with Multi disks, some disks have stuff on that I do not understand..(could be levels in the game) they are PRG.. One game I really want to load up is the Turrican games, tried Disk and Tap files.. Cheers if you can help.
Thanks. :) The PRG files on the disk are most likely levels and data that the main program loads after it is run. The SD2IEC is not a full emulator of a real drive though, so most software that uses internal fastloaders and such simply does not work (with a growing number of exceptions). For using multiple disks you have to put all disks that belong to one game in a folder and also add a "AUTOSWAP.LST" textfile that has the names of the D64 images in it. Rod (The future was 8-bit) has made a handy little summary of SD2IEC functions you can go through here: www.thefuturewas8bit.com/index.php/sd2iec-info
I also highly recommend getting some sort of SD2IEC compatible fastloader (Final Cartridge 3, Epyx Fast Loader, JiffyDOS etc) because it significantly speeds things up and adds nice keyboard shortcuts for loading stuff etc. I'm using a FC3 on my C64 most of the time. For this video, I used SDBrowse (linked in the video description) as the program to browse the SD and start games. It has a built in fastloader that's not too bad but it's generally a bit fiddly to use. Hope this helps you get more out of your SD2IEC and your C64. :)
Well done old chap. Can I ask what temperature you set for your desoldering station? I have the same gun and struggle to get the RAM out because of the ground plain, but don't want to whack the heat up for fear of cooking the ICs.
I have it set to 350C at the moment. Works best for my "style" of desoldering. I touch the joint briefly until the solder melts and wiggle a bit while using the pump. Then I quickly pull away to not overheat the component. Took a while to get to a temperature/timing combination that worked for me.
I read somewhere that it's better for the ICs to get hotter for a shorter period of time than to get exposed to lower heat for a longer period. I don't really know if that makes any sense. I haven't cooked an IC with my method yet. ;)
I've been told you can keep heat to a minimum by not desoldering adjacent pins, i.e. jump skip four or five pins at a time and keep switching sides.
Really struggling with those ground pins on the RAM chips, too much copper on the board drawing heat from the gun. Annoying since the 20-pin CIAs came right out.
Probably a good idea to skip pins or pause between desoldering. For some ground connections, I turn the heat all the way up and try to do the desoldering as quickly as possible. I found that adding fresh solder or flux and also wetting the tip with solder helps a lot to get more heat to the actual joint.
Thanks for the tip Jan. This board will be either stripped or on fire before too long.
+dantootill Hope you get it to work again without burning it. ;)
Nice fix Jan and nice video;)
Thanks. :)
Saubere Arbeit Jan! Sogar mit Antistatik band wie es sich gehört :D
+Vittek Antilles Danke! Bei der Antistatik bin ich leider noch nicht ganz so konsequent, wie ich es gerne wäre, aber ich arbeite dran. ;)
Interesting video. I have a C64 that shows text in the wrong colour in some applications. If I manually write text on the BASIC screen, all the colors are fine. Colours in games are fine. It's only certain text-mode applications. It passes all of the diagnostic tests. Freaking weird.
This was very helpfull , thanks
Turns out I have to find a NEW PLA.
Oh, glad I could help. :)
Hammer! Dank dir.
+Dieter Löffler Sehr gern. Danke für's anschauen! :)
nice fix
Thanks!
great channel. great video. all the best :-)
+The Great Jonzini Thank you very much! :D
Bravo
Good vid there Jan very informative.🤔.kim
as a kid my first computer almost got to be a (used) C64, however it had a fault just like this.
my parents and relatives (who were the previous owners) tried a while to fix it but really were at a loss about what to do. last time they used it, it was just fine, they said. i remember them switching the fuse on the board and hoping it would maybe change it.
and i would power it on and notice that some characters changed on the screen when i pressed some keys, and hoped that maybe if i do that long enough, at some point it would eventually return to the normal screen :D of course it wouldn't
in the end that lead to me having to wait a while longer until i got my first computer, which then was a 286 IBM compatible
Oh, that's kind of a sad story and a long wait until your first computer. :/
well I don't exactly remember how long the wait was, and I am not sure if you are making an assumption here when you say "long wait"
at the time all that happened, the 486 was the high-end on the market, Pentium was not out yet but not too far in the future.
i got a used machine so it was affordable and to get me accustomed etc.
but of course, back then there was no Pictorial Fault Guide online, etc...
such resources we have today to fix these old machines are really amazing... imagine what you would have given "back then" for such a wealth of info
I remember my first PC was a Pentium 150 MHz in around 1997 (when it was "state of the art") so the 486 was one or two years earlier probably? I'm not very PC savvy at all (I still am surprised every time I want to upgrade something that there are new CPU sockets and next generation PCI buses... ;))
It would have started me on electronics very early on probably to have all that information available back in the day. It's like being in wonderland now having all the forums and info available. ;)
I'm not completely sure when it was, but it must have been 1993 or 94.
Looking on Wikipedia, the Pentium was already introduced in 93...
but probably the first couple of years it was so expensive it wasn't really an option for most people, at least for the home. So 486 pretty much was top of the line for people with a normal budget.
I remember that when Windows 95 came out, late 1995, there were still discussions in PC magazines etc. about how you would need a Pentium to have a really smooth experience with it, while it was okay on a 486. however, around that time, 1995/96, was when the Pentium also became more affordable. (and had TV commercials, not sure if any processor was advertised on TV before... may have been the first!)
by the way, Win95 even worked on a 386, even though that wasn't officially supported; but it ran very slowly, froze up frequently... I tried that once back then ;)
From looking at the thumbnail picture only and not watching the video, I would guess an address pin on the character ROM has a problem, effectively ORing the screen code with 16.
After watching a minute and a half I've changed my mind... it's fun to guess at these things.
I'm an old C64 user and tinkerer myself. I've seen a couple of C64 boards long ago, but none of them had the regular 74LSxxx ICs renamed to Commodore's own MOS-brand. By the way these chips aren't just "compatible" with 74LSxxx but plain relabeled, I'm sure. Normally such a thing is done to hide the design of the circuits. However it looks very pointless to me since there were tons of C64 boards without that rebadging.... You can get brandnew ones for example at your local Conrad.de store for a few eurocents...or at some little electronics components store.
If I understood the story correctly, MOS produced the chips in-house to further cut the cost (probably a couple of cents per C64 unit). It turned out that the quality was inferior pretty quickly and Commodore went on to buy off-the-shelf parts instead. I've seen at least two C64 boards with the MOS logic chips on them so far.
Alright, thanks for the details. Quite interesting!
:)) Lovely as you call the screen "garbage" :D In fact, that is "garbled"... which means that everything is messed up... :D
Yes! I keep confusing the two. Looks like garbage, too. ;)
Jan Beta Indeed :)) Nice fix, congrats!
nice Lips TV
WHY.am.i.watching.this........can’t...stop...watching....
*Evil laugh* ;)
Good work, now upload this issue w/screenshot to that website..
Thanks! I have sent Derbian an email already (before I published the video) and he's going to add it soon. ;)
ALWAYS be suspicious of MOS branded 74xxx logic. They have very high failure rates; so much so that I often replace working chips just as a preventative measure. Of all of them, MOS 7708 (74LS257 multiplexors, U13 and U25) seem to be the most prone to failure that I've seen..
Yeah, I heard about that. I actually had a C64 with one of the multiplexers being broken a while back. Took me a while to find out then. Now I learned that these MOS chips are always prime suspects. ;)
Can I ask that you speed up all your de-soldering work, please? It's not boring, I just really like the sound it makes when sped up.
Haha, I love that sound, too. :)
lol@LIPS
Just my strange kind of humor. ;)
RUQTY
Okay
The easiest way to troubleshoot is simply to swap chips into a working unit.
very bad video,incomplete and cut
+Serpico Sicilia What should I have included that you are missing? I thought I had shown the whole process at least briefly.
You've really gone downhill since you gave up superheroing and took up internet trolling.