07 July 2019, 15:04 | #1 |
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A600 391029-01 Power Supply - integrated Voltmeter for +5V and +12V
This weekend I decided to mod an A600 391029-01 power supply to have an integrated voltmeter that shows either (switchable) +5V or +12V
I have an 391029-02 for my A1200, but this is the 'heavy' type with with potting compound - so very hard to mod : I might chip away at the potting compound at a later date. So for this project I acquired a 'light' 391029-01 power supply, which does not have any potting compound in it: I wanted to be able to show both +5V and +12V. Maybe at a later date I can figure out how to get -12V shown too. The voltmeter I have is only for one input voltage source, so I needed a way of switching between the two. The voltmeter has a 5 digit display. This will allow me to see how much the voltage reading fluctuates. The schematic I have for this setup is: I won't bore you with the build pictures here, but they see be seen at: https://imgur.com/a/xNegdzd Here's the finished build showing +5V and +12V readings, with the switch on the side of the power supply (sorry for the poor lighting): The +5V reading was very stable, albeit a bit high, and sat at a constant 5.262V (sometimes 5.261V). The +12V reading was not so stable with the last two digits tending to fluctuate frequently. I don't whether this is typical or not, or a sign of a particular power supply capacitor needing replacing? |
07 July 2019, 18:02 | #2 |
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I think it's better to get a display where 5v & Amps are shown instread of 12v since this voltage doesn't really matter so much, and is used by floppy drive only where amps are really important, especially, if accelerator card, ide & CF Card are in use...
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07 July 2019, 18:20 | #3 | |
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Quote:
I'll still have the 5V/12V switchable for the voltmeter part, but obviously the ammeter part will just have to be for the 5V. |
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07 July 2019, 19:48 | #4 |
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I added a 70mm 12V fan, but connected it to 5V instead. Ideally it should be temperature controlled, but for now this'll do.
I just hot glued the fan to the grill at the top of the case. |
10 July 2019, 10:54 | #5 | |
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Quote:
It has to be mentioned however, that there are a couple of issues with using the same type of panel meter that measures voltage and current: First, they typically measure current on the ground side, which means that while you can see the voltage on the 5V rail, the current display will be the total current on all three rails. Naturally, the +/-12V rail currents will typically be low, but it's not guaranteed. And second, current is measured by checking the voltage drop across a resistance. This normally doesn't cause much of a problem, but on the Amiga, the ground and shield are common at the PSU and usually connected via a choke at the Amiga. This means that the voltage drop will in part be negated by current flowing through the shield path, thus giving you an inaccurate low reading on the ammeter. This can be resolved by disconnecting the shield at the PSU end, but I prefer not to do that as it's been designed to be connected for noise and protection reasons. |
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10 July 2019, 11:23 | #6 | ||
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Thanks, some really good points have been highlighted for me to get my head around!
Quote:
Quote:
Again, can this issue be resolved by having the 5V line going through the ammeter instead, if technically possible? |
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10 July 2019, 11:34 | #7 | |||
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Quote:
Quote:
Yep, the shield and ground are connected within the Amiga, via a ferrite choke with close to 0 resistance. Quote:
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10 July 2019, 11:44 | #8 | ||
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Quote:
Quote:
If powering it 'independently' (bottom diagram) , albeit with the same 5v line, would this still have the issue you describe? |
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10 July 2019, 13:12 | #9 |
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Ah, ok, sorry I didn't catch that. Fair enough, there are many different types of power supply that Commodore used - I haven't seen them all.
The independent supply really needs to be independent - to use the same 5V rail you need to treat it as shared. However, it looks like your meter can't measure on the positive rail in either configuration, so it doesn't really matter. It will end up reading the combined current for all rails. If you don't have any 12V loads other than the motherboard, you can probably say that that's around 0.1A so not a huge error really... |
14 July 2019, 01:22 | #10 |
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Found this on Ebay: Lot Nr. 264244745026
Donno may it be used or not, its basically the same solarmon suggested Last edited by 8 Bit Dreams; 14 July 2019 at 01:32. |
17 July 2019, 14:26 | #11 |
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I got the combined voltmeter and ammeter and installed it:
(It probably needs calibrating - there are a couple of potentiometers on it) This the +5V voltage and usage when loaded in to ClassicWB via CF, and with an 8MB memory expansion card in 4MB mode, and with an internal Gotek with an 2.42" OLED screen and trackball. The wiring of this setup is now as such - which is getting quite busy and a bit hard to manage inside the power supply: |
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