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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 8th Jun 2019, 8:42 am   #1
Pietro123
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Unhappy Distorted image with Commodore 128

I've recently opened my C128 to try fixing some problems after months of disuse. Some keys didn't work, the spacebar missed the springs so it was constantly pressed and the computer didn't load my programs from cassette after I recorded them (all in 128 mode). I've fixed the spacebar with a spring I took from a pen, cut in two and placed them in the right places. I've also found out that the keyboard wasn't plugged in correctly, wich could be the reason some keys didn't work. I still don't know why it didn't read my programs after I recorded them, since the play/record head of the datassette was aligned. Now that I've booted my C128, it displays this weird distorted image, which is mostly green and red, accompanied by a very loud humming sound. What could be the problem? Perhaps I've reinstalled the heat sink incorrectly after cleaning the motherboard? Could it be the power supply damaging the computer? Or even just a bad cable (I've used an 8-pin DIN to scart)?
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Old 8th Jun 2019, 10:47 am   #2
SiriusHardware
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Default Re: Distorted image with Commodore 128

Missing or misplaced earth / 0V connection in your DIN to SCART lead, possibly? Did you make up the lead yourself, and has that lead ever worked at some time in the past?
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Old 8th Jun 2019, 1:02 pm   #3
Pietro123
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Default Re: Distorted image with Commodore 128

No, I haven't made it up myself, I bought it online. It was meant to be used with a Sega Master System, and it works, but it doesn't work with the C128. So they probably use different connections. I'll try to rearrange the connections and see if it works. Thank you for your help
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Old 8th Jun 2019, 1:35 pm   #4
SiriusHardware
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Default Re: Distorted image with Commodore 128

Yes, unfortunately I think it would be very unlikely for two such different manufacturers to assign the same signals to the same DIN socket pinout. I didn't have much luck finding the sega DIN socket pinout, but here is some info about the C128 video output here:

http://www.softwolves.pp.se/cbm/mask.../scart.en.html

It seems to suggest you need to be using the DE9 output (if you have one) for output to SCART.
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Old 8th Jun 2019, 6:06 pm   #5
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Default Re: Distorted image with Commodore 128

The loud humming would prompt me to check the ripple on the power supply. Commodore power supplies are notorious for failing and taking out sensitive chips. If the machine hasn't been recapped you should consider that too.
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Old 8th Jun 2019, 8:20 pm   #6
SiriusHardware
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Default Re: Distorted image with Commodore 128

As the OP mentioned, it turns out he is using a lead meant for a Sega system. I would not go looking for any hardware problem with the C128 until a correctly wired C128 lead has been tried. (By the way: Good to have you back).
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Old 10th Jun 2019, 1:38 pm   #7
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Default Re: Distorted image with Commodore 128

Quote:
Originally Posted by SiriusHardware View Post
As the OP mentioned, it turns out he is using a lead meant for a Sega system. I would not go looking for any hardware problem with the C128 until a correctly wired C128 lead has been tried. (By the way: Good to have you back).
Yeah, but you know me, I don't always want to read the facts before I jump in
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Old 11th Jun 2019, 11:24 am   #8
Pietro123
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Default Re: Distorted image with Commodore 128

Today I tried using my Commodore again, and the power supply makes a weird noise, kinda like there's something moving very fast inside of it, it sounds similar to a small motor. Could this mean the power supply is failing?
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Old 11th Jun 2019, 1:05 pm   #9
SiriusHardware
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Default Re: Distorted image with Commodore 128

If it is a switched-mode type power supply then it would not be unusual for it to make a high-pitched whistle, but it could also mean that the power supply is working too hard due to failing capacitors, as Slothie suggested.

However: Please try an alternative video connection method - a video output lead made specifically for the C128 - before you go looking for hardware faults on the C128. I don't know if that machine has an RF-out connection intended to go into the antenna socket of a normal TV - if it does, try it like that and see if the machine seems to be working normally that way.
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Old 11th Jun 2019, 1:34 pm   #10
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Default Re: Distorted image with Commodore 128

It doesn't sound like a high pitched whistle, it sounds like there's something small moving inside of it, like a glass being shaken very fast with an ice cube in it.
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Old 11th Jun 2019, 1:39 pm   #11
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Default Re: Distorted image with Commodore 128

Good description, but it could still just be the transformer laminations rattling. If you remove the power from it and shake it, do you hear anything rattling around loose inside?
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Old 11th Jun 2019, 3:43 pm   #12
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Default Re: Distorted image with Commodore 128

Quote:
Originally Posted by Pietro123 View Post
It doesn't sound like a high pitched whistle, it sounds like there's something small moving inside of it, like a glass being shaken very fast with an ice cube in it.
An Amiga power supply should be almost silent. I'd be very wary about connecting a noisy one until I was sure it was OK. See GadgetUK164's recent video: https://www.youtube.com/watch?v=xmkvfrImI8Q&t=0s
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Old 11th Jun 2019, 4:23 pm   #13
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Default Re: Distorted image with Commodore 128

I'm pretty sure the C128 used a sort of hybrid power supply with a switch-mode supply for 5V DC and a transformer for 9V AC. I'm sure I remember loose laminations in these when I repaired computers for a living (though it was some time ago, so my memory may be playing tricks with me!)
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Old 11th Jun 2019, 4:32 pm   #14
SiriusHardware
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Default Re: Distorted image with Commodore 128

Quote:
Originally Posted by Slothie
...An Amiga power supply should be almost silent. I'd be very wary about connecting a noisy one until I was sure it was OK. See GadgetUK164's recent video
Yes but... it's a Commodore 128?

Unless the PSUs were the same for both machines, in which case excuse my ignorance.
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Old 11th Jun 2019, 5:08 pm   #15
Pietro123
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Default Re: Distorted image with Commodore 128

Quote:
Originally Posted by SiriusHardware View Post
Good description, but it could still just be the transformer laminations rattling. If you remove the power from it and shake it, do you hear anything rattling around loose inside?
Yeah, I've tried shaking it and there's clearly something loose inside. Also, I think the previous owner of the C128 opened the power supply, since it's wrapped in duct tape. It could be the reason.
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Old 11th Jun 2019, 6:06 pm   #16
Slothie
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Default Re: Distorted image with Commodore 128

Quote:
Originally Posted by SiriusHardware View Post
Quote:
Originally Posted by Slothie
...An Amiga power supply should be almost silent. I'd be very wary about connecting a noisy one until I was sure it was OK. See GadgetUK164's recent video
Yes but... it's a Commodore 128?

Unless the PSUs were the same for both machines, in which case excuse my ignorance.

Oops. just ignore me, I'll just stand in the corner!
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Old 11th Jun 2019, 6:30 pm   #17
SiriusHardware
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Default Re: Distorted image with Commodore 128

Ignore who?

Pietro123, I think your rattling noise is going to be broken pieces of plastic, probably parts of the plastic posts which the case fixing screws should screw into. That would explain why the PSU is now held together by tape.

All this is diverting you from the real question, though, have you tried a proper C128 video cable, or have you tried connecting the computer to a TV via an RF lead and tuning it in to see if it looks as though it is working that way? (You would need a TV with an analogue tuner of course, and I assume this C128 was made for your country originally)?
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Old 12th Jun 2019, 6:47 am   #18
Pietro123
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Default Re: Distorted image with Commodore 128

Good morning!
Today I found an RF cable, so I tried it and after tuning the TV, it displays a totally normal image, so the Sega cable was the problem. Now I tried loading some games from cassette, in C64 mode, but it doesn't find them or sometimes displays "out of memory error" (wich could mean I have to replace at least one RAM chip). Also, I noticed the datassette unit stops for a fraction of a second every 5 seconds, and when I move the datassette's plug while it's rewinding, it stops. Should cleaning the pins work?
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Old 12th Jun 2019, 9:06 am   #19
SiriusHardware
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Default Re: Distorted image with Commodore 128

I have a saying, 'always try the simplest thing first', so yes, try gently cleaning the contacts. It may also be possible that the cord/cable between the datasette and the computer has an intermittent break in it.

The Datasette itself may also have a physical - intermittent fault - you will just have to try to eliminate these things one after another, starting with the easiest (cleaning the contacts on the datasette plug and the corresponding contacts on the computer). Don't use anything really harsh, like sandpaper, because the contacts will be plated or 'tinned' - you don't want to scrape that coating off.

Good result with the video check, so the next step is either to buy a ready-made 128-to-SCART cable or make one, if you feel able to do that. I think they are probably so cheap that it is not worth the trouble to make one.
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Old 12th Jun 2019, 7:00 pm   #20
Pietro123
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Default Re: Distorted image with Commodore 128

Ok, I'll try cleaning the contacts and see if it works. Thank you!
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