Using visual clues to figure out which chips are bad
Sometimes diagnostic routines lie and give you false readings and that was the case with this broken C64. So let's use our eyes (to look at the symptoms) and some math to figure out which chips are actually causing the issues.
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Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
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RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
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The bad sounds of a SID becoming a SAD chip.
Yeah no kidding. I felt SAD having to hear sounds from a chip that was clearly on life support.
In this particular case, SID stands for: "Sid is dead".
FYI: The MT RAM chips are Micron (as in Micron Technology, Inc.). The dram chips in question would have been from just three years after they opened Fab 1, and the 64Kbit chips were, in fact, Micron's very first dram product. The primary problem is they're sensitive to overvolting, with only .5v of headroom. The C=64's problematic PSU's (as they aged) meant that Micron's chips are more prone to failure in the C=64 than in some other machines.
INTERESTING!!!
That SID was putting out some amazing hardcore techno/gabber noises. Perfect overdrive distortion.
that's what I was thinking. Someone could write some absolute bangers that take advantage of it's brokenness.
as a die hard Apple II/Mac guy with zero interest in Commodore stuff back in the 80's, you still got me to watch a 45 minute troubleshooting video. A+. more please.
Since that one SID is obviously broken and on its last legs, I wonder if it wouldn't be a good candidate to try to rejuvenate via the reflow oven? I mean, it's probably *not* going to work... but the SID needs to be replaced either way. Keep making these vids - I never tire of seeing how you troubleshoot these C64 repairs. Thanks!
What I did notice, that before Adrian replaced the SID, it wasn’t indentified in the SID tune player, but the replacement was
I've always wondered if dead SIDs are due to bad bond wires, and if so, would it be possible to decap and rebond the die.
I was going to say something about the screen code values vs. ASCII, but looks like you got there in the end. 🙂
On CBM machines, PETSCII codes (i.e. altered ASCII codes) and screen codes are two different things. PETSCII codes are used in programming (CHR$ ASC), in character strings, BASIC tokens, files and all I/O. On the other hand, the SCREEN CODES are the bytes used only in the Video RAM so that the VIC video processor can find the right characters in the dedicated ROM.
That snake(~ish) sprite on your 8 bit dance party prg did not work correctly with the bad SID, but it worked fine with the good one. So, I am guessing it is not just a screen ornament, and is somehow functionally connected to the SID?
Senses certainly help with diagnosing faults in electricals and electronics, sight to see failure, smell to smell burning, touch to feel for heat, hearing to listen for noises, and taste, well, you're just weird if you're licking stuff... :P
I bet candy is one of the best diagnostic tools. The procedure is probably (1) place candy in mouth, (2) stare into space, (3) suddenly get an idea for what's wrong.
I prefer to "Use the Force!".
@@Capohanf1 If not The Force, at least The Schwartz...
That SID chip is in violation of the Geneva convention
But at least all channels work. In my first, then already out-of-warranty C64, back in 1986, only one (or two?) worked so for example the "piano" puzzles were impossible to solve in Impossible Mission, as those sounds used just one of that/those faulty channel(s). (And I couldn't think of getting it repaired due to the high costs.) But at least Commando's, Paradroid's and Uridium's main tunes / sound effects used the working channel(s) so I didn't miss THAT much in those particular games :)
If it gets hot enough, it'll violate the Geneva convection... 😄
"Look with your special eyes" "MY RAM!"
Now that's an old reference. I don't think many young zoomers will get that one.
That commercial was hilarious.
More of this audience would have seen it than not, I’ll wager.
@@zerobyte802Oh for sure. Most retro enthusiasts tend to lean either Gen X or Millennial.
Ooh. I like your method for cleaning the flux. I always tear paper towels or leave cotton fibers behind when trying to wipe it up, but scrubbing over the top of a paper towel seems like a great idea.
@43:42 The standard Amiga (without custom graphics card) also has memory-mapped display, but the problem is it has no text mode, which is what you used to find the faulty RAM chips. About Sinclair, the ZX81 has text mode, but the ZX Spectrum does not. Thanks for another great video! Please feature more Sinclair classics.
These kind of fault-finding videos are always very enjoyable, Adrian. Very good to explain and demonstrate the first principles by hand, which should help people understand what the Dead Test and Diagnostic cartridges are trying to automate. Thanks again :)
I used that method all the time when repairing video terminals. As you said, bit-mapped characters make this method impossible but those that use an actual character ROM and rely on a table, it works well.
In a future chapter, Master Adrian 'Sensei' will repair another Breadbin with his eyes closed. 😄 (Using just touch, hearing, smell and taste). 😊 Good work! 👍👋
36:19 it's the Bad SID Remix :D
I'm not an electronics repair technician, I'm a mechanic but it's amazing how many problems I've diagnosed simply by using my eyes and knowing what to look for! People always seem to be so amazed and I'm like dude all I did is look lol
Mechanic here too, 20+ years. I agree 100% with your experience. Open your eyes, ears, nose and it’s amazing how much stuff you can quickly diagnose! 👍🏼👍🏼
"If there's a problem, Yo I'll sove it. Check the MOS chips before I desolder" 😅
ICE.. ICE.. BAAABY!!
Impressive knowledge on how to break down the issues of theses!
@39:00 you should also check using AC mode in case of high AC ripple on the DC rails, also an AC ripple can result in a higher reading in DC mode in some cases.
seconded.
The PETSCII and screen codes are actually different. PETSCII is converted to screen codes with the PRINT command.
Yeah, I wanted to comment this. The at symbol has screen code of zero (but petscii value is decimal 64). Though the dollar sign and the space is the same, for example. Well, by heart now, so I can be wrong with the actual data here ....
The sprites for the 8 bit dance party come and go randomly and as far as I remember it should be continuously running.
Always good to see these great videos!
I love that you took the time to put a warning up, and to make sure you made goofy faces in the camera, instead of ducking the audio to not need the warning. And by love, I mean question what's wrong with you.
Classic Digital Basement. Love it.
It's not using one vs two bytes, it's the number of cycles required to access something on zero page. The 6502 includes a zero page addressing mode that can only address the first 256 bytes of RAM, but it can do that faster because fewer moves are required with the one byte address.
The "@" is a desperate attempt by the computer to tell you "The error is @"
Screen codes are different from ascii codes, as mentioned in the programmers reference manual on pages 376 to 378, the ascii codes are on pages 379 to 381, which is why they show different symbols when you poke them to $0400 😁 Just fyi, may be helpful to your viewers 😀 Great vid Adrian, please keep the C64 vids coming when you can, my favorite computer from back in the day 😎👍
I'm kind of new to your channel, I really appreciate what you do. It's an awesome channel and you're a really nice guy, I'm glad you decided to do it full-time. You're going to be very successful.. doing what you love is the most important thing in life.
Great demonstration of how to determine which RAM is faulty. So many different implementations across all the retro systems but most have some sort of analogous troubleshooting that can be performed. Thanks!
Thanks for the c64 videos!
Many years ago when Commodore 64s were still being used I used to repair them and never had the luxury of a dead test cartridge or a diagnostics cartridge.
Great job man. 👏
Character ROM holds the bit patterns for each character. The first bit pattern (bytes 0-7) contains the pattern for the @ symbol. The next pattern (bytes 8-15) hold the pattern for A, etc... When the VIC II chip needs to know what to display at a certain character cell, it reads the screen memory at the corresponding location and gets an "index" value into the character ROM. The pattern will start at index*8+base (where base is the location of the character ROM in address space, or RAM if the VIC II is set to point elsewhere). These "indexes" are known as screen codes. PETSCII itself has nothing to do with character display. It is a modification of the ASCII standard used for data communication (printer, modem, screen, etc...) . The KERNAL ROM will convert the PETSCII codes to screen codes whenever something is printed to the screen. The $ and @ symbols appeared because the bad RAM was causing the VIC II to get the patterns from the wrong part of character ROM. Also, my first thought when you played those SID tunes on the bad SID was "those are the metal versions of the SIDs." Laughed when you mentioned the same thing at the end of the video. :D
Sometimes it's cool to hear and see how things malfunction. You can sometimes hear and see some really cool things!
That was the funniest sounding broken SID of all time. I laughed so hard.
While it's been at least 0x20 years since I've done 8 bit work in assembler and machine language debugging, and none of it C64, I did notice a few things. The corrupt screen characters NEVER changed position (or what was displayed), and assuming that the C64 used memory mapped I/O for its display (which it does), that told me that those specific memory addresses had corrupt data. While it's possible that support chips, like the multiplexer chips, could cause that problem, a bad logic chip isn't typically repeatably bad in a way to give the same result every time. That indicated bad RAM, which turned out to be the problem. When you got out the PETSCII table and analyzed what was happening, the 0x20 -> 0x24 ($) made sense. However, the 0x20 -> 0x40 (@) did not. Two failures at the exact same address? I immediately wondered what was in the character ROM at 0x00, and as you later discovered, was the @ sign. I appreciate your posting of these troubleshooting videos. I've done very little of this kind of work since leaving the engineering field after the "dot com" implosion. Watching these is scraping some of the rust off, and I'm getting the itch to dig my 'scope out of storage. Maybe a little Depoxit for the brain??? :)
FYI: Screen RAM values actually can't be the same as ASC/CHR$ value, as ASC/CHR$ also uses control commands that are not displayed, but executed. E.g. PRINT CHR$(13) sends a RETURN, CHR$(147) clears the screen. Others move the cursor, turn on/off reverse mode, etc.
Great video! Learned a ton from it. Thank you!
Even Adrian's sid-dance was a bit distorted. 😂 Thanks for the laughs!
Awesome troubleshooting!
37:05 That is without a doubt the worst sounding SID ever. what a shame.
Yup, encountered @ a lot of times myself (the most important / common example is a hex monitor / mem dumper with the char ROM representation of each byte - full of @'s for 0's of the, after powerup, untouched memory areas - along with FF's, both in blocks) so I immediately assumed it's 0
Some computers use different Character$ look up tables depending on if they are PRINTing to screen or POKEing to screen. ASCII has control codes from 0-31 and the Character set from 32-127, but when the computer POKEs to screen the char set is from 0-95.
Given some of the strange behavior of this machine you may want to check if it's been overclocked.
Decoding method is very interesting. Can never learn enough
I feel like screen codes and ASCII must be different on every computer, because ASCII has to include control characters whereas screen codes don't. In the case of the Commodore 64, the screen codes also have to include the inverted characters because color inversion isn't actually something the VIC-II can do, which conveniently allows BASIC to have access to them to represent some of the control characters inside quotes.
Man i love your repair videos!, specially if they are about commodore, i will love to see you repair a msx machine, although i know not many where sold in the us, but it was the machine i grow up with :)
Interesting to go through the process once again. Did my eyes deceive me or was there a problem with the snakey thing on 8bit dance party near the end? Keep up the fascinating repairs (although I've never had a C64)
Indeed, I noticed this as well. Seems more may be wrong with this 64 (maybe the VIC-II) and would love for Adrian to investigate this further.
Thank you for your videos, Adrian! If you have the Commodore 64 User's Guide, Appendix E (Pg. 132) has the Screen Display Codes. Nice tutorial..
idk, that SID sounded beautiful :P
The fact that the bit pattern seems to flip flop from the lower four to the top four bits makes me think that it might still be a multiplexer issue.
@28:30 - Yeah, Adrian... you're confusing the "Screen Display Codes" (Appendix E, Page 132 in the C64 User Manual) with the "Ascii and CHR$ Codes" (Appendix F, Page 135). - The original Commodore manual does not call them PETSCII characters, that is a mashed-up acronym coined by us.
Y'know, I was just thinking about the diag harness and cartridge and had an idea.... you could add one more cable to the sound output, tell the SID to output a certain series of square wave, and check it with fairly basic circuitry. The noise channel would only be checked for level this way though, the square wave would let you check for level and consistency. You could detect the right frequency via high level counts over time, and then compare similar values in slices to see if any drops occur. Might even then adjust the level to near a cutoff point as a rudimentary consistency check, count wave peaks at a touch under and a touch over to see if any don't cross the threshold. It'll never beat the ear test, but you could get a negative go on a given SID before subjecting your ears to it.
Next week: Repairing computers with brain waves
Thanks for the video.
This works very well on the C64 where video memory is part of the main 64KiB of RAM and there is a text mode of some form. However in the 8bit era, there were machines which don't work that way. Eg. the ZX Spectrum doesn't have a text mode and the video memory is always part of the first 16KiB of RAM which is implemented as 8 4116 chips. So if the fault is in the upper 32KiB, it won't be visible as garbage on the screen. MSX machines also have separate RAM chips for the video memory. In short YMMV :)
Had a 64 doing the same thing. Each time Diagnosis had different bad RAM. Ended up replacing the MOS and other logic chips and no luck. Then ran Dead Test and it Identified that U23 was bad and that turned out to be the only bad RAM chip. It was an MT chip of course.
Mine got power supply zapped. Am using a modded c64 DTV as a backup machine though.
you can also update the note adding a date when you be able to fixed it :D
This helps me a lot. I did not type any of this I grabbed this from the internet then dropped it here . I am not very good attyping or spelling Decision Flowchart . A decision flowchart is an essential tool for simplifying complex decision-making operations. It helps individuals or teams come to consensus by dividing the task into accessible, systematic steps and arranging them in an easy-to-follow flowchart design.2 A decision flowchart is essentially a blueprint of what needs to be done to solve a problem and helps in analyzing and balancing the effects of a particular choice.1 Flowcharts can help break down a complex problem into smaller and simpler steps and organize them in a logical order, making it easier to see the big picture and the details, and to avoid confusion or ambiguity.0 .
M.T. RAMs, where you learn to compute without RAM! (sung to Empty Rooms by Gary Moore)
I'd love to see you fix acrade boards 🙂
Pretty much any 16 bit system will have difficulties trying to diagnose bit flips by character display as most do not use character modes. IBM PCs do use a character mode but bad bits in main ram probably wont show on screen as the screen buffer is in vram and if the screen shows corruption try a different video card first before thinking it could be a main board problem. If bit flips occur with any video card then yep might be bad system ram or something else on the main board like bad bus transceivers.
Hi Adrian. You kind of look like some member of the Enterprise from ST:TNG 🙂
I thought that too, number one lol.😅
He taught Geordi everything he knows 😂
Where is Rammy and Dead Parts bin?
When my system was bad I had to replace the bit value 128. It had some stuck 1's and some stuck 0's. It was the only chip that was bad, but I replaced all 8 of them because MT ram. I did start with that one. So yeah a failure mode with stuck 0's and stuck 1's is perfectly normal. And honestly you should just replace them all. On mine I ran a BASIC program that checked RAM by setting FF and comparing the results. And then setting 00 and comparing the results. I had like 39 errors in 32k of RAM.
Nice fix. I have a Commodore 64 with blank screen. Swapped out the PLA chip, no difference.. that's about the extent of my troubleshooting. Not sure what to do with this C64, donate it, sell it for parts, etc... Suggestion for you, when you write a note on that sticky note, perhaps put a date on there so you know when you did any work on it... Great video!
I'd keep it just in case you can get it to someone that can fix it.
Nice diagnosing! But where is your Retro Chip Tester Pro to verify the desoldered DRAM's?
After you replaced the SID with the known good one and ran the Dance Party, it was having trouble showing the sprite animation that normally happens. It flickered on several times briefly, and then after several seconds, popped in and worked okay. So maybe the VIC has an issue in the sprite generator?
One of the SID tunes is called "koeleskab" which means refrigerator in Danish.
You need one of those IR cameras. Vevor has a very affordable / good one, and you can save the video to an SD card
Your intro is so awesome
Genius!
Someone needs to step up and put together an independent C64 Ram tester, independent by ensuring voltage is present at the memory and then each chip is written/read and compared at a given clock speed "which I think is important" to highlight marginal chips. In fact looking at the circuit diagram all the other main chips could also be tested independently seeing most of the routines have already been worked out by a few Testing cartridges..
Great 😊
YES! ❤
I have this c128 that has no video. I suspect it’s a bad IC, everything is socketed. All components are new and I have been very careful building this computer. This is a 128 neo. If I can send it to you I’m sure it would make for another great video. Let me know if you’re interested.
If I was repairing and I saw MOS and MT, I'd replace it all, then diagnose. Maybe it fixes it maybe it doesn't, but it's a great place to start.
Bad RAM, bad RAM! What ya gonna do, what ya gonna do when Adrian comes for you! 🤣
How do you get that top view of the camera of the board? I want to do that for my own teardown documentation.
Oh my, that poor SID.
I fought the PETSCI issue while working on DDM this summer. The values in screen ram are Screen codes which don't easily map to PETSCII.
Great work and diagnostic. I am having trouble debugging a Z80 computer without any method of input or output. How would you go about it. I tried building a RC2014 to give me input and output and using an extra Z80 card without the processor fitted and using a 40 pin to 40 pin ribbon cable to connect the processor signals. Now I have to write some code to see what is happening. No easy when the Z80 computer uses a PIO to switch eprom and ram. Do you have any suggestions?
your test cartridges did you make them or can we get them someplace
I like how the Restore key is used for "panic" What does that do?
That SID is so bad - keep it for future projects.
I think I recall that Robin @8_Bit showed that the "@" in the upper left is normal and it's just invisible on certain systems.
Adrian, me and my other half (Wayne) salute you Sir. Your videos are the most interesting and informative on the tube. We would love you as a neighbor (or neighbour 😊) here in the UK. Great stuff. Wayne and Nina (Ipswich, Suffolk, UK) 👍👍👍👍👍😊😊😊😊❤️❤️❤️❤️❤️🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🫡🫡🫡🫡🫡🫡
that sid was trying haha, poor sid chip.
43:50 You forgot the lid for the VIC-Yard...
Regarding those M/T RAM chips and the MOS chips that you left in the machine, by leaving those in place, aren't you setting yourself/someone else up to have to deal with more troubleshooting in the future? In other words, wouldn't it be best to "futureproof" that C64, by replacing those chips with new reliable ones? My guess is that you're providing content that hopefully helps someone else troubleshoot these wonderful machines, and that for machines you intended on using, you'd probably "futureproof" them as described?
Heavy metal SID music = Machinae Supremacy from Sweden. 😉They're using a SIDstation. Sidology (1-3) has some great video game music covers. Their best cover is Gerudo Valley ("GERUDO VALLEY (Metal Version) | Machinae Supremacy")
Would be nice if DEADTEST cartridge had UART output, so it would work like Diagrom in Amiga.
Your dead/dying SID chips could still be useful for powering things over at THIS MUSEUM IS (NOT) OBSOLETE.
Szanuję 😎
What happened to test / confirm with the RTC?
The thumbnail with your shirts gives me Picard vibes.
🖖 greetings cpt. Picard 😂 sorry i could not resist the tempting😂
I don't have good hearing, and often cannot tell a SID chip is bad, when you say so. But that one today....oh yeah, I definitely could tell it was bad.
Do these black/gray rings he is wearing have a meaning? I've seen one of this on another youtube channel - though can't remeber which one.
I just assumed they were silicone wedding rings.