Commodore 64 troubleshooting part 1 the basics - multimeters and alcohol

[@williammckeever4790]

Great video. Everyone should always start with the basics before you start replacing chips, etc.

[@davemcd2579]

Absolute legend. I recently picked up way too many C64s and some other stuff in a bundle and have been stepping through on a first pass test of what there. One today was real rough looking with no signa of life. Googling how to test the voltage rails led me here and with a bit of follow along I could quickly see that the 5V put of the switch was great but the 9V was dodgy. Quick spritz of Iso and it burst back into life and seemingly works better than half the others I tested. Cheers mate, appreciate it greatly, learned some new stuff and have at least one good breadbin now.

[@StripeyType]

There are very few videos which have such high "replay-value" - I definitely imagine watching this several times over!

[@jandjrandr]

I like the instructions to watch out for the U17 and U18 locations because they can be swapped between the 250425 and 250407 board revisions even though the rest of those boards are very similar. Mixing those up could be disastrous for the PLA, feeding it with 12V. The same applies for accidentally reversing the 6581 or 8580 and those ICs are worth a significant amount these days.

[@david.godlewski]

studying for when my two "untested" commodore 64s arrive and I'll inevitably need it.. thank you for these videos!

[@peterbilt3385]

Brilliant guide for someone like me who has purchased 3 C64's, one working and the other 2 projects and don't want to go too far buying additional kit just now.

[@kyokorn]

Idolo ! man! is great explanation, I recently get my first commodore 64, sadly is not working but your videos is a very effective way to start the troubleshooting, thanks for this!!!

[@markusfritze]

Thanks for this. I think another good idea is to take many many pictures before doing anything (and make sure they are in focus). I would then remove the SID and store it safely before doing anything else - that thing is too expensive to take any risks and the machine works fine without it.

[@TheRetroChannel]

Yes, good idea. And usually I'll pull the SID first, unfortunately if there is an issue chances are somebody has already powered it on with the SID in and fried it anyway. Thank god for the ARMSID

[@DrDavesDiversions]

Great additional tip! Just yesterday, I referred back at a good quality photo of my C64 motherboard from 6 mos. ago while working on it again. Also helps a lot when we take a break for days too while things are disassembled.

[@michaelcarey]

I had a faulty C64 power switch causing all kinds of weird faults. As soon as that 5V rail starts to drop all bets are off. RAM chips are one of the first to flip out with low voltage.

[@troytaylor623]

I was having problems with getting low voltages on my c64c and I swapped some of the 12v voltage regulator thinking that was the issue but realized I wasn't getting the right voltage into it. Saw this video and cleaned the switch with IPA and presto worked! Thanks for this video!

[@konturgestalter]

Just rewatched it. really good. would be great to see more of these troubleshooting tutorials on different devices!

[@koztech]

Thanks for this! Yeah there's a lot of text-based guides, but having a visual guide is extremely beneficial!

[@MrRepeters]

Good video. I love "Deoxit" for switches and sockets. Also, looking for "cold solder joints" for switches and items being pushed or joggled.

[@Epictronics1]

Great video. To avoid breaking the clips on the C64C, I tend to only lift the upper part of the case slightly and then push it forward

[@g-wolf9445]

Excellent work keeping this simple for people who don't have a background in electronics troubleshooting. If you had started talking about ESD straps and how things like the shields are another ground some people would be upside down before they even got started with figuring out the problem with their C64. Thank you for posting this video!!

[@trevorjex3146]

Thank you for the video, this is going to be super helpful to test out my c64 i just got. Checked the voltages and chips for heat, waiting for the AV cable to come in the mail 🤞

[@g-wolf9445]

Thought I'd put in another comment. I ordered a C64 on Ebay a few days ago that wouldn't power on and would you believe it, the trick with the isopropyl alcohol for the power switch worked! Both DC and AC were putting out zip. Cleaned the switch on both sides with isopropyl alcohol and the thing started working with no hang ups. I feel so bad for the person who tried to fix it before! Thank you, thank you, and THANK YOU!!!!

[@TheRetroChannel]

Hah, that's awesome. Glad to see another one saved, and I assume you got it at a good price 😁

[@doktor6495]

Very nice! You train the new generation of C64 repairers! ;-) Many greetings, Doctor64!

[@TheRetroChannel]

Oh hi Doktor64, nice to see you here. Thank you

[@donaldblakley6796]

Yes! Finally someone who is very througal with helping us c64 lover's start from the beginning:) 2 dirty switches wow. Very educational. Video saved. Also you keep me motivated as well. Thanks

[@donaldblakley6796]

Hi, sorry for bothering you again, I think I know why my board worked after changing 2 rams, then went back screen and dead test won't work. Pin 4 on the cassette port has 6.23 v. Yikes! My other 3 say 0v on pin 4, or .03

[@TheRetroChannel]

Are you sure it's pin 4? 6.23V is roughly what the cassette motor receives on pin 3. If it's definitely on pin 3, then perhaps there's a short between pins 3 and 4

[@donaldblakley6796]

Yes, pin 4 on cassette port. The one on left side of the gap

[@TheRetroChannel]

Alright so just so we're on the same page. The cassette port has 6 pins, looking from the rear of the board there's pin 1 and 2, then a gap then 3,4,5,6

[@donaldblakley6796]

Ok. My mistake. From the rear of the board, it's pin 3 that has 6.23v . Sorry:)

[@MindFlareRetro]

OMG. It takes me so long to comment. Anyway, great series. Super informative, especially for those at home that might not have a plethora of electronics test equipment. Great stuff!!!

[@UncleAwesomeRetro]

Very nice video :) I had to subscribe and I am looking forward to the next one.

[@nickolasgaspar9660]

Prevention is better than cure.....so always buy a retro computer that doesn't have the commodore budge on it....lol. Great series. The methods are applicable to any retro computer.

[@konturgestalter]

excellent series!!!!

[@neilhans8510]

Hello, I am in the United States and it's where I purchased my Commodore 64 in the early 1980's. After years in storage, I wanted to get my C64 going again. I purchased a new power supply after reading I shouldn't use the original/old power supply. When I turn on my C64, I get a blank screen although the red power light turns on. I checked the AC and DC voltage on the pins in the 7-pin DIN male power supply connector and they seem OK…4.9 VDC on pin 4 (or I've seen it labelled as pin 5) and 12.4 VAC on pins 6 and 7. Following your video, and specifically at the 5:40 mark is where I run into an issue. I plugged the power supply into my C64, but didn't turn on the C64's power switch yet. I test the bottom/inner-most contacts on the power connector (CN7) on my C64 and get 4.9 VDC--that seems fine. But when I test the top contacts, I get anywhere from 3.8 to 4.4 VAC. I assume it should be around 12.4 VAC as when I tested the pins directly…but I don't. Why? The connector (CN7) looks OK, there isn't any physical damage/scratches/chips that I can see. Could it be a bad connector (CN7) or a faulty power supply? Thanks in advance for any guidance.

[@TheRetroChannel]

Could be a bad connector, or more likely a bad power switch. You could try plugging and unplugging the cable a bunch of times to see if it gets any better, likewise turning on and off the switch a number of times may help. If you have some isopropyl alcohol or contact cleaner you can spray some in the socket. The other possibility is broken solder joints on the socket or the switch, you would need to pull the board out (and remove the bottom RF sheild if attached) and look closely for any obvious cracks on the joints or movement when you jiggle the socket or switch

[@neilhans8510]

@@TheRetroChannel Thank you. I removed the circuit board from the case and I don't see any solder joint issues. I sprayed some DeoxIT into the connector (CN7) and in the switch (SW1). Later, I tested again and get the same results on the connector (CN7). The strange thing is, when I have the power supply plugged in but the C64 switched off, I tested the 5 VDC regulator. I assume it should read 0 volts since the switch is off, but I get around 0.27 volts. I unplug the power supply, then it reads 0 volts. Also, when I tested the connector (CN7) for AC voltage on the top two contacts, as stated earlier, I get around 4 VAC--not good. What's weird is when I swap the multimeter probes, I get 0.3 volts. When testing AC voltage, I assume it shouldn't matter which probes I use, unlike when testing DC voltage. So I assume the connector (CN7) or the switch (SW1) is the issue. Which one do you think I should replace first? Thanks again.

[@TheRetroChannel]

Yeah that's really strange with the AC measurement. It should read the same as you suggested. The small voltage on the regulator could just be from the filter caps, and maybe they drained completely by the time you unplugged the cable EDIT: sorry, just noticed you mention testing the AC on CN7. That's before it hits the switch, so maybe it is the connector. If it reads the correct AC voltage before you plug it into the 64 (just probing the pins on the connector itself), then it's certainly sounds like poor contact inside CN7.

[@svenpetersen1965]

The toothbrush is not a tool, that you really want to use inside electronic devices. Could be static, could kill your ICs. For cleaning IC pins, I would recommend a fiber glass pen. And for the sockets, a tuner spray, which is less aggressive than a contact cleaner is doing a good job. If you want to brush some thing, there are pretty cheap (maybe 5$) sets of antistatic brushes. The switches are bad pretty often. Sometimes, it helps to open the switch and to clean the contact bits. I have seen switches that had really eroded contacts. Especially on C128 (higher current). I have watched the two episodes of this (the 2nd first) and I like them. One can fix a not low percentage of the broken C64 without a fully fledges electronic lab. Especially the sockets were already bad in the 1980s. I have received my first fiber glass pen from a Commodore technician back then.

[@gam85191]

Great video mate. Do you do C64 repairs? I got one that needs looking at, just don't know who does this in Australia

[@TheRetroChannel]

Cheers. Yeah I do repairs, but before we get into all that, what is the issue with your 64?

[@gam85191]

@@TheRetroChannel I'm getting not signal at all. I've done the basic tests and seem like all is good

[@TheRetroChannel]

@allanm5556 Ok, if the voltage regulators are outputting 5V and 12V then you may have a dead VIC-II. Could also be a clock generation issue. Up to you if you want to continue trying to troubleshoot it, or I can take a look. You can find my contact details on the channel homepage

[@eightsprites]

Really good! Thanks

[@infernomast5882]

My commodore was in an addic for 20 or more years, it works it turns on but i get a screen of characters thats are in cubes, they take up the whole screen

[@TheRetroChannel]

Check the pictorial fault guide for something that looks similar to what you are seeing. Link is in the video description

[@gb7767]

IPA doesn't really get rid of oxides ... you might get some of the surface stuff, but using a proper contact cleaner, preferably de-oxit is going to give much better results

[@TheRetroChannel]

Yes very true, I should have at least recommend that. Personally I hit the sockets with contact cleaner and the IC legs with the fibreglass pen when necessary

[@cesar8ramirez]

Excellent work. I’m getting 4.2 ohms when the power switch is on and I’m guessing this maybe the main issue. I tried your alcohol idea but to no avail. Would hate to disolder the whole deal and put it back on. Is there a reason to add the shield back on after removing?

[@TheRetroChannel]

Yep sounds like a bad switch and if spraying alcohol in it did not work then it will need to come off. The RF sheild isn't required unless you're running an amateur radio station

[@kevbh0406]

Really enjoyed the video as I played along testing my own C64 (bread box). My son and I revived my C64 with the arrival of a new power supply, but the computer stopped working after about an hour. When I tested the regulators inside the machine, the DC regulator tested similar to your result, but the AC regulator is showing 26 volts, much higher than the 10 I was expecting. Any suggestions on my next step? I’m getting a variety of colored or flashing, or stripped screens now when I try to boot. Thanks in advance for any advice.

[@TheRetroChannel]

I'm not sure what you mean by AC regulator. Are you talking about the AC reading on the user port? If so then yes, that should read as around 10V with your meter set to AC. Otherwise it suggests a problem with the transformer in the power supply, as I don't know any other cause for that high voltage

[@kevbh0406]

@@TheRetroChannel Thanks for the quick reply! The voltage at the User Port appeared correct, I was referring to the test at 10:21 in the video where you tested the “Voltage Regulators” in the lower right corner of the computer. They are small black squares and you tested against Pin 2. That’s where I showed a 26.4 volt reading for AC.

[@TheRetroChannel]

Ah ok, both those need to be tested with the multimeter set to DC. Double check that they both show the correct output (5V DC and 12V DC), and let me know how you go

[@kevbh0406]

@@TheRetroChannel - Doh! I’ll try again, but in DC mode when I get home tonight and report back. I’ve owned the computer since new when I was in middle school, but this is the first time I’ve seen the inside! And obviously my use of a multimeter has been limited… thanks again!

[@kevbh0406]

Well, I’m making negative progress. Retested the regulators but no reading at all. Looks like I managed to blow the internal fuse some how. Just ordered some replacements and will start over when they arrive in a couple of days. In the mean time, I’m enjoying more of your videos!

[@duckmanito]

Hey, firstly thanks for doing this video. I got in my hands a C64 exactly like the one you repair. I am seeing strange voltage in the user port, I get 0.47v DC measuring pins 1 and 2. Same thing when I measure the output of the switch button (what you do in 24:31). Resistance test gives me 0 ohms, contrary to your board. Voltage regulators gave me good numbers too. I tried with isopropyl alcohol 99% without luck. Does this mean that I should replace the power button or maybe other component is failing? The video chip is pretty hot, but is my first C64 so I have nothing to compare with. My multimeter doesn't have the Hz option, so this is all I can do for the moment. Thank you again.

[@TheRetroChannel]

If you're seeing 5V at the input to the switch (the bottom leg towards the front of the machine) but less than that on the middle leg when switched on, then almost certainly it's a bad switch. You could bypass the switch by connecting those two legs together with an alligator clip (make sure the clip doesn't touch any of the other legs). Do this with the C64 unplugged, then short the legs, turn the power on and connect the power cord last

[@Then00bhunt3r]

I'm getting 5.1V DC and 7.4V AC on my PSU and about 0.3 from both voltage regulators. I'm guessing this means the PSU is bad, but isn't it normally the DC side that fails and supplies an over-voltage? Aside from replacing the PSU cable, is there anything else I should check here?

[@TheRetroChannel]

Yes it's very uncommon for the AC transformer to fail. If you're seeing 7.4V directly from the plug without being attached to the 64, then I'd suspect a bad cable or joint somewhere between the transformer output and the DIN connector

[@donaldblakley6796]

Hi, this one I'm working on now has 12v at the power supply and 11.3 v at user port. Is that bad? DC is perfect. Thanks

[@TheRetroChannel]

A little higher than usual but it should be fine

[@brunocosta3023]

Hi I have a commodore C64 Wien i turn on pc i have image looks ok but my tape dataset dont work when i try play, rewind, forward all…Then i try with a dataset of a friend of mine and didn’t work too. Is there a problem with comunication with commodore and dataset? What i can do please?

[@TheRetroChannel]

Try first pushing fast forward or rewind and then power on the C64. If the motor briefly runs and then stops it's likely an issue with the CPU. If the motor doesn't run at all then it's likely an issue with the motor power circuit in the 64.

[@kurtreber9813]

I've bought 2 separate PSU by now, trying to get my old C64 back to life. Both say they deliver 9v AC but actually deliver 13.5! Am I missing something? Is there a part of the computer that actually gets 13.5v AC and I'm just measuring the wrong part? Could it be that European PSU deliver 13.5v for European C64? I had to buy C64 PSU from Europe as I don't see any available in the US. I did try it anyway, and something starts smoking, so I know something isn't right.

[@TheRetroChannel]

Oh wow, that's definitely not right. Which PSUs have you been using? Are they rated for 120V for the US?

[@bakevv6967]

I also have c type commodore and the ready screen boots up but the cursor isn't there and the keys don't work. I saw on a forum that it may be caused by a bad CIA chip, have you ever come across this problem?

[@TheRetroChannel]

Yep, highly likely the CIA at U1 is bad. If both CIAs are socketed you can confirm this by swapping them around. They are very sensitive to static electricity and tend to get killed by accidentally touching the joystick ports when swapping joysticks

[@bakevv6967]

@@TheRetroChannel thanks for confirming, I really appreciate it!

[@zandersan49]

I think I found the problem with mine. I'm only reading 60hz on the cpu. It is not warm at all. The power led also does not light up. What do I do?

[@TheRetroChannel]

Check your voltages at the user port. No power led suggests there is no 5VDC coming in. The 60hz you're seeing may just be a tiny bit of the AC line frequency if you're in a 60hz country

[@zandersan49]

@@TheRetroChannel the user port voltages on the left notch are fine, but on the right its 0.58 volts, 0.5 what you said it should be. Probably also worth mentioning the problem with mine is that my display is just black.

[@TheRetroChannel]

It should be 5 volts or there abouts, not 0.5. Sounds like there could be an issue with the switch, power connector or power supply. You could try flicking the power switch on and off a few times and see if that voltage changes at the user port, if so then the switch is likely bad

[@MS-ho9wq]

This is Comment 64 👍

[@brianclimbs1509]

As an amateur radio operator, I find your disdain for RF shields quite alarming.

[@X-OR_]

Unsubscribing, Too much Commodore only content. Looking for more Apple II stuff...Good Luck !!