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Post by mrbombermillzy on Dec 1, 2016 20:16:05 GMT
Finally, got some time to make my own version of a C128D PSU, as I have had the poor computer sat in the corner for several months now. Anyway, I managed to scrape together a 12/5VDC switching supply and a separate 9VAC transformer. I put both into the 128D casing and wired up to the motherboard power header. On switching on, the disk drive (or that area) was giving some nasty sounding humming noise, so I immediately switched off. The board was tested with a 'proper' 128D PSU and ran fine. I have the correctly set pinout: 9VAC (2 wires) and the 12v, 5v and 12/5 GND. Am I doing something stupid here?! (I seem to have had a bit of trouble with PSU's lately.)  Im pretty sure that it doesnt matter which 9VAC line goes to either of the 9VAC terminals. Apart from that, the 12, the 5 and the DC GND lines are correctly set on the board jumpers. |
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Post by Pyrofer on Dec 2, 2016 0:02:48 GMT
Do you NEED the AC if you have 5v and 12v???
I know the flat is slightly different but I ran mine powered from a 12v/5v dc2dc supply hooked up to the internal power connector (used by the 128D I believe) and had no AC connected at all.
Double check all your connections go to where you think they should go. Then look back at an original PSU and double check what is actually connected where.
Did you test it with a "proper" PSU after the humming noise? Fingers crossed it's all still good.
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Post by mrbombermillzy on Dec 2, 2016 7:01:08 GMT
I dont have the luxury of any extra 128D PSU's to double check with anymore. The 9vAC for the SID is not essential I suppose. However, I even tried without the 9VAC lines connected, but still the same. Quadruple checked the lines are located correctly. Im pretty sure they are. The only other thing I can think is that on the original PSU board, there is a 2 pin header from the 12V with a resistor in line which connects to the power LED on the front case. This is not being connected as I dont have the resistor plumbed in. I didnt think it would hurt running it without the LED plugged in...? |
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Post by Pyrofer on Dec 2, 2016 7:32:39 GMT
Check, check and check again. Look at the schematic here, I think this applies to your on3, www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/310378-1-left.gifThe 6 pin post connector has no 12v in. It has 9vac and 5v. You can run the 128 on EITHER 9vAC+5vDC OR 5v/12v DC. Make sure the grounds are correct. Make sure 5v is correct. Check the PSU has enough power, you are looking for 3amp or so here. Personally I would just use 12vDC on pin 5 of the post connector as I didn't have the 9vAC when I last tried, but 5v12v powered my 128 fine. the 12v DC inside the 128 is generated from the 9vAC, so you need either/or, not both. |
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Post by mrbombermillzy on Dec 3, 2016 9:07:50 GMT
Ive been hunting for an SD card so I can take some photos. A picture is worth a thousand words, so they say! So here is the original C= unit: The LED header is on the bottom left of the board.  Now, to focus on the output wiring to the mainboard header:  The 12 and 5vDC GND lines are together here so Ive kept them together on my wiring too. Notice how the 128D also has the 12VDC lines (for the floppy drive I presume). Heres my wiring of the 12/5VDC PSU and the 9VAC transformer:  The brown and cream coloured wires are the 9VAC and the rest go to the 12, 5 and GND of the other PSU.  The PSU wires are NOT colour coded as expected. On my donor PSU, yellow is actually GND (connected to black on the mainboard header lead). 12V is red (connected to the yellow of the board header wire. Red is actually 5V). The only dodgy thing on my part is the bridging over the blown fuse on the 12/5V PSU! :s (I know, I know, not a great idea. However, the PSU was fine and the 128D was fine. It should be ok for a quick test with everything wired correctly).  As far as I can tell, Ive wired it all up correctly. Like I said, the only questionable issues are: 1.) Does not connecting the LED actually matter? 2.) Does it matter which way round the 9VAC wires are connected? (There isnt really a live and a gnd wire on an alternating current). Thanks for any help and for pointing out if Im being really thick!  |
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Post by remark on Dec 3, 2016 14:51:15 GMT
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Post by mrbombermillzy on Dec 3, 2016 16:41:46 GMT
Thats exactly what I have wired up:
Pins 5 + 6 are wired to the 9VAC transformer (brown + cream/off white)
Pin 4 is 5VDC (red coming off the board and white when past the junction box)
Pin 1 and 3 the 2 GND lines are black (going into the junction box to yellow the other side)
Pin 2 is 12vDC (yellow coming off the board and red when on the PSU side of the junction box).
Ive checked and checked. I wouldnt normally post something as trivial as this... I must be missing something!
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Post by mrbombermillzy on Dec 3, 2016 18:35:22 GMT
Here are some photos of me checking the voltages at the pins. I cant break it down much more than this!  Around 11.5VAC seems slightly high for the 9V line, but it may be like that when not under load.  5.21VDC on the 5V line seems ok.  12.2VDC on the 12V line.  This is just to show a clearer picture of what the wiring is doing. I did attach a video lead to look at the output from the VIC when switching on. It was quite a garbled rolling multi colour mess, so I didnt leave it on. Somethings not right! |
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Post by remark on Dec 3, 2016 19:03:54 GMT
What are the current ratings for your new PSU?
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Post by mrbombermillzy on Dec 3, 2016 21:36:26 GMT
Umm... I threw the cover in the bin a couple of days ago for the 12/5v PSU  However, it was around the 2-3A mark. The 9VAC transformer is 1000mA. |
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