• Please review our updated Terms and Rules here

Dead c128 power supply

megaboyx

New Member
Joined
Feb 26, 2011
Messages
7
Please help. I hooked my old C128 up for the first time in a few years. Worked great last time but now, nothing. I checked the voltages on the power supply cable coming out and get nothing. So I figure it is the supply. I took the lid off and snapped some pictures. I don't see any problems and the fuses look good too. Any thoughts? All I have is a voltage meter and a few simple tools. I couldn't make sense of the SAM's schematics at all. My power supply is model 310416-05

Please take a look at http://www.mypicx.com/02262011/c128_power_supply/
 
Even though the fuse looks good, it still could be bad. Try pulling it and replacing it with an identically rated one. I once had a C128 power supply that was given to me as "bad". The fuse was visibly intact and even showed continuity. I replaced it and the power supply started working. After examining the old fuse, it appeared that the element in was oxidised somewhat. So it would show continuity, but there was acting like a resistoror something weird. Why it simply didn't pop the fuse, I don't know.
 
You're working with a simple linear supply, which is good--those are very easy to work with.

I'm assuming that you're using this schematic or something similar.

The first thing that I'd do is to see (with the power off) if there's continuity on the primary side of the transformer--use the continuity tester (low resistance range) and see if there's continuity between the line plug blades. There should be a very low resistance showing.

If that doesn't pan out, check the continuity of the primary filter inductors.

Next, with power applied, using the AC range of your voltmeter, check to see if there's voltage on the secondary windings of the transformer. If so, the expensive items are eliminated.

Look over the PCB carefully; wiggle (slightly) some of the larger items, particularly the large inductor to see if a solder joint has failed.

The remaining problem areas are minor, but let's get the majors out of the way.
 
That's great information. I'll try to see if I can order some more fuses. About the other stuff, line plug blades, filter inductors, etc. I don't know where or what that stuff is. Where the power is first connected to the unit there is a black cable marked L, a white marked N and a black that goes to ground. After that there is a black box marked (BV 2165 1A) then a green box marked (F 1772 410-2000/) then the 250V fuse and a couple of blue boxes that are hard to read. I just don't know where to put the volt meter. I guess the big box with copper wiring is the transformer? On the other side there is a coil with copper wiring too and two capacitors and a very small tube with copper around it by the 125v fuse. Don't know where the inductor might be either though.
Also the continuity function might not be working right since when I put the leads together it pegs to the right and won't adjust down to 0 with the knob, even with fresh batteries.

One more thing, I'm having a hard time finding a 1.5a 125v fuse online. All they have is 1.5a 250v. I wonder if that will work?
 
Last edited:
At this point, if a visual inspection of the solder side of the PCB doesn't reveal any bad solder joints and the fuse is good, I'd get help.

Work on power supplies often entails making measurements with power applied. A mistake could be fatal to you.
 
Yeah, I don't want to fool around with it with it plugged in. It has been unplugged for a couple days now and I am just putting the ohm tester on the underside but not the capacitors. I don't know what those 2 blue boxes are I mentioned but no current gets through there on the tester when putting on the same box, but when putting on the same pin on either box, top of one and top of the other for example, current goes through. I hope the fuses work though because I dont want to pay 80 dollars for a new power supply which is what people seem to be trying to sell them for on ebay.
 
One more question if you please. Take a look at this picture. http://www.mypicx.com/02262011/transformer_lines/
I have been visually tracing the power around since I took it out of the shell. I see it goes into the transformer on one side. On the other side as you can see in the picture, one of the 3 lines are connected, the other 2 are broken. I suppose these are important? Should I solder them back together?
 
Yes, the 1st 2nd and 4th lines from the left are certainly broken. I just wonder how to solder them back. I don't have a soldering iron right now, will have to buy one... I'll see how it goes. Thanks for the help.
 
I Appreciate everyone's help on this problem. I replaced the fuses and I soldered any connections that looked broken but I still get no power coming out of the unit. I don't know what I should check next. I would like to do the things mentioned above if I knew exactly where on the board to place the leads. It's killing me having all my C128 equipment and software and all and it going to waste because of a power supply. If anyone is willing to trade or sell one who knows how to fix them, I also have a couple C64 power supplies and a couple 1451 and 2 1571 drives.
 
Back
Top