IIGS power supply 12v at 11.5, should I worry about it>

[lowlytech]

I picked up a IIGS advertised as working.  As with most 25+ year items I like to recap at least the power supplies.  I never turned the unit on myself before starting the recap due to the main filter cap having a puffy top.  I got everything recapped with the lowest ESR Nichicon caps I could find at Mouser, along with the y2 Rifa just incase it felt like releasing a smoke screen.  Also while desoldering several of the caps I got that unique fishy smell from several of them, so a recap at least was probably a good thing. 

When finished, I connected to the IIGS for load, I am measuring the 5 volt voltages at +5.02, but I only get +11.52v for the 12 volt rail.  I can't locate any adjustment pots on this supply at all.   Do I need to be concerned with the low 12v supply?  I am not really sure what uses 12v in this system.  I do have an external 5.25 and 3.5 floppy, but other than that, plan to use a CFFA for a hard disk and a gglabs 4MB memory card with no other expansions.   The power supply is 699-0126, Astec.

 

[cruff]

Well, the +12 supply is only 4% low, so may be within tolerance, but maybe only until you attach some hard disks that need it.  Some quick searching didn't turn up a schematic.  Since you are going to use a CFFA and nothing else you are probably good to go.

 

[lowlytech]

Thanks for the reply.  I have tried to search this issue with low voltage and the only thing I have came up with is someone saying that that main filter cap could cause the voltage drop.  I know these new caps have a 20% tolerance, maybe the 330 isn't exactly 330 and closer to 300.  Just out of curiosity I am going to yank that cap and run it on my peak ESR meter and I have another 330 cap I am going to try to see if it makes a difference at all incase someone else runs into this same issue.

 

[lowlytech]

Well the original 1987 cap with the blown top still measures @ 323uf on the Peak tester, the new cap comes in at 309uf.  I had ordered two different series of nichicons from Mouser and tested them all and I don't get a value higher than 311uf and infact one of the new 330 caps measured as low as 293uf.   So putting the old cap back in is the only option I have to see if it makes a difference on the 12v rail and I don't like the idea of that due to it being the one cap that physically looks the most questionable of the lot.  The 5 volts is spot on, so I don't know if the main filter cap would only affect the 12v output or if it would alter the 5v rail as well.   

will roll with the 11.52 and see if any stability issues arise.

 

[cruff]

Taking a quick look at the IIgs schematics, about the only thing on the motherboard that uses +12V is the speaker driver circuitry.  It is also supplied to the card slots, but a CFFA probably doesn't use that voltage, so you may not care that it is a bit low.

 

[lowlytech]

Thanks cruff for looking into what the 12 volts is for.  Makes me feel a bit better about the low 12 volt output