Hello C128 :)
Didn't come for some time 'cause of school.
So, recently my C128's PSU fried. Apparently, it was already quite damaged by the last owner...
It looks like it's pretty hard to find these as spare (With a european plug) so, I opened it to diagnose it.
I found that one of the voltage regulators had exploded and burnt a small part of the PCB of the power supply.
I'm good enough at soldering to replace it but I need your help to give me the technical details of that regulator so that I can order another one.
I'll try to solder the replacement part back in place, but with that burn, I might have to do some jumper connections and hang it on the case with some electrical tape.
Here are some photos of the culprit and the burnt PCB:
(http://img294.imageshack.us/img294/8721/dscn2450y.jpg) (http://img294.imageshack.us/i/dscn2450y.jpg/)
(http://img257.imageshack.us/img257/7799/dscn2449l.jpg) (http://img257.imageshack.us/i/dscn2449l.jpg/)
(http://img18.imageshack.us/img18/435/dscn2451w.jpg) (http://img18.imageshack.us/i/dscn2451w.jpg/)
Every other component looks fine, except that regulator.
Would anyone be able to provide me with the characteristics of that precise part ?
Also, I received another C128 recently (That's my third ^^) but the previous owner (One of my neighbors) hooked it up using a C64 PSU...
Seeing that it didn't work, he gave it to me because is doesn't know anything about electronics, so he can't repair it.
I would like to know if there was a fuse that protected the whole unit from the different pinout of the C64 PSU or if the unit was completely gone...
Thanks again for your help :)
The markings on the voltage regulator don't mean anything to me... the bottom number looks like a date code, but wouldn't 1984 be before the introduction of the C128? Of course the PSU could have been built with old stock parts.
Anyway, from the last C128 PSU that I serviced, I remember the 9V AC output came through a transfrormer (no regulator) so that leaves only the 5V DC as the possibility. In that case, the standard part would be a 7805. These are available from various suppliers with different power (amp) ratings. Get the most powerful one you can afford! According to the C128 PRG, the worst-case power drain on the 5V supply is 22.47W. So you should get a regulator with at least 4.5 Amp capacity (22.5W / 5V).
I don't know what to say about the other unit. How did he plug a C64 PSU into a C128 ? One plug is round and the other is square!
Thanks :)
Looking at the schematics (In the service manual), I also think that it's for 5vDC.
I don't know how he managed to hook that up. I think the european C64 psu plug is square. (At least, that the memory I have from the only one I saw. I d'ont own one yet. But I'm looking forward to it, if any of you has a boxed unit to sell ^^)
Anyway, I'll look at this when the PSU is repaired.
CAUTION !!!
The burnt part isn't a 3pin regulator IC like 7805 or similar.
It's a Thyristor used to protect over voltages on the 5V output rail.
(usually the part is named TIC106)
It is triggered by the zener-diode (in one of the photos between two resistors on top and bottom) whenever the Voltage of the 5V line reaches a critical level, and then shorts the 5V line to ground, which should blow the fuse and thereby protect the attached C128.
If this part is burnt means - someone replaced the original fuse with a bigger one & the switching transistor has (most probably) a short, leading to a output voltage of ~20V (the primary input to the step down converter) instead of 5V.
Quote from: timscampi on June 23, 2010, 01:51 AMI think the european C64 psu plug is square.
The British C64 and the German C64 that I have both use round PSU plugs.
Truly,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug (http://videocam.net.au/fcug)
July 24-25 Commodore Vegas Expo 2010 - http://www.portcommodore.com/commvex (http://www.portcommodore.com/commvex)
Wonder if it was an A500, A1200 or A600 power supply he attempted to plug in ?
QuoteWonder if it was an A500, A1200 or A600 power supply he attempted to plug in ?
That's possible (He has a bunch of old Commodore computers)
Anyway, after looking a little bit more, I think the power supply is really messed up. I don't even know how it powered up in the first time.
And, yeah, it happens to be a thyristor. Didn't notice it at first (It really looks like a voltage regulator...) but, looking at the schematics, it seems it is.
The huge coil (In the sort of metal box) detached a side itself from the board (Probably due to it's weight.) I should have taken more care of what I was doing ^^
That thing seems to complicated to repair so, I'll think I'll just buy another one... When I'll find one.
I'll probably end up doing one based on the schematics and using the connector on the one I have, considering it's pretty hard to find on ebay.
I wouldn't head for a used original replacement - it most probably end up the same (or comes already damaged).
[rantmode]
Sorry Commodore, but the power supplies you delivered, are the worst (cheapest designed) ones I came across ever since, and responsible for 80% of damages to the devices which they should power.
[/rantmode]
(here in Germany we used to call the ones for the C64 - "doorstopper" which they did better than to power anything sensitive such as digital equipment)
A better solution to the above, provided that you have some electronics & soldering experience, is to buy a modern switching power supply that delivers 30 to 50W @ 5Volts in additon to a simple unregulated transformer for 9V AC / 500mA, then de-solder the cable with the plug [square one] from the fried PSU and connect it to the new setup.
Funny thing is, in all the dozens upon dozens of C= machines I've had (and power supplies) the only one that ever failed was a PSU for an A500 (and that was my fault, coffee doesn't go well with electrical equipment in general.......) I've never had any issues with them beyond that! I'll be the odd one out and say (IMHO) that the power supplies are quite reliable. Some of the ones I have are hitting nearly 30 years old and still working perfectly!
Yeah coffee and electricity don't mix well. Reminds me of the time that one time my friends stuck a nail in the catridge port of a Plus/4. (You can call him an idiot, it won't bother me.) It burnt the fuse in the Plus/4 and fried some other components in the Plus/4, but the PSU survived no problem. In the few milliseconds before before the fuse blew, there were some really pretty colors on the screen :)
I have to agree that CBM PSUs, in my experience, are normally trouble-free. The only problem I've had is with a unit that had been physically abused (dropped from several feet). It just needed a jumper wire or two soldered across some broken traces on the circuit board.
I've had more problems with the internal 5V regulator on the C64 than anything else.
Try plugging a printer into the external drive port of an A500..... oops.