11 September 2011
|Just when I thought I knew almost everything about what I do, I go and surprise myself with a whole bunch of TCs being worked on.|
There are two fan types, very subtly marked so as to fool the eye... the APPLE P/Ns are 607-2113 and 607-3650. The DELTA part number remains the same, which had fooled me with the false belief that they were electrically the same.
I had ploughed my way through 8x PSU repairs and a similar number of fan conversions. I try to get all of the soldering out of the way first, so I can concentrate on other forms of TC mayhem not involving molten metal. Unusually I decided to simply check the converted fan assemblies by plugging them into my spare TC fan socket. Small pair of snipe nosed pliers and push the plug into the socket. The fan should run at a constant speed and this was the odd bit - half the fans converted (with a 33 Ohm resistor to drop the supply voltage) ran faster and louder than the others?
I assumed with the first fan that I had a naff resistor in the bunch supplied and the value was out - such things can happen but are very rare. Four fans running fast and loud needed a better reason than that though!
There was a difference in the part numbers - but that was all I could see. Some testing with a variable resistor showed that the -3650 version of the fan ran at about the same speed and made the same noise as the -2113, if the dropper resistor was raised to 43 Ohms. It would run much slower and quieter but would not ‘start’ from scratch or if stalled with a prodding finger tip!
The proper controller I keep planning is now needed... I simply must get on with it!
I think there are probably between 30 and 50x modifications out there where the cooling fan runs faster than it should and thus makes more row! Sorry people! It fortunately does guarantee to keep the PSU cool... so is not a cause for concern.
I have now exceeded the 150 mark on conversions. It is very tiring believe me... this weekend has just gone and all I’ve done is sat inside fixing things.