Re: My sick 2/10

From: Scott Lewis <slewis1962_at_email.domain.hidden>
Date: Mon, 29 Nov 2004 21:42:38 -0600

Just a few comments.
1. The +300 volts is generated on the video board. The potentiometers for brightness and focus are located in the power supply for convenience. There is no +300 volts present when the power supply is out of the Lisa. If you look closely at the power supply board you will notice there are no connections between the video potentiometers and resistors (R1 to R7) and the other power supply components.

2. The trick to measuring voltages on the power supply when it is removed from the Lisa is a little bit more complicated than connecting the +5v standby (pin 20) to on/off (pin X). You should also connect +5v sense (pin N) to +5v (pin M) through a 220 ohm 1/4 watt resistor. Pins M and N are opposite pins 11 and 12. I would also suggest putting a 220 ohm resistor between pin 20 and pin X instead of shorting them together.
The last thing needed is some load resistors. The Lisa power supply is a switching power supply and will not function properly without a load. The Lisa Hardware Manual lists the output as +5v @ 4.00 to 8.00 A and +12v @ 0.35 to 2.00 A. The -5v and -12v do not require load resistors. You can get a card edge connector from Digi-Key to connect to your power supply. The correct connector is a 22 position 44 contact with .156" contact spacing (3.96 mm). I believe the part number I got was EDC305440-ND which has solder eyelets. You can also get one with a solder tail EDC305442-ND.
I would suggest using a 1 ohm resistor for the +5v load. This will draw 5 Amps which is within the range listed in the Hardware Manual. You will be dissipating 25 watts of power so you will need a pretty large resistor. I used four 1 ohm 10 watt resistors wired as 2 sets of 2 resistors in parallel then wired the sets in series to create a 1 ohm resistor network capable of dissipating 40 watts. For the +12v load I would suggest 20 ohms which will draw 0.6 Amps and dissipate 7.2 watts of power. I used two 10 ohm 10 watt resistors in series which is more than adequate. I found the resistors and perf board at Radio Shack but you can probably find them at most any electronics supply store.
You should assemble these parts on a board and run some 20 ga wire from the edge connector to your board. Then all that is needed is to defeat the safety interlock on the power supply and plug it into a wall outlet.
Once I built my test board I was able to properly test my power supply. Before that I was getting incorrect readings similar to what you are getting.

Scott

On Nov 25, 2004, at 11:30 PM, Quanda Computing wrote:

> Ok, I did some more troubleshooting.
>
> I removed the drive cage. Thwump got a little louder.
> I removed the RAM cards. Thwump got a little louder again.
> Removed the CPU card. Thwump got even louder.
> Removed the entire card cage. Nothing happened when I pressed the
> power button. I would assume this is normal because the power button
> connects to the card cage :P
>
> I made a recording of the sound.
> http://users.tc3net.com/gperkins/Thwump.wav You can hear the thwump
> followed by the click of the switch.
>
> I also noticed that right after the thwump from the speaker I could
> hear what sounded like the high voltage PSU in a monitor when you turn
> it off, that kind of quick high pitched sqweak. So perhaps there is a
> short somewhere else? I had taken Lisa mostly apart a while ago, and
> didn't see anything that looked out of place. I also turned her upside
> down and shook her really hard and no bits of metal fell out, so I'm
> gunna say no paperclips are lodged down in there.
>
> I will try checking voltages next. I would like to check at the line
> supplying the Widget, and if possible, right at the power supply.
> Which lead(s) are the power leads in the Widget connector? Is there
> any way I can 'trick' the power supply into turning on when I have it
> out of the system, so that I can measure voltages right at the edge
> connector? Looking at the schematic David provided, it looks like one
> of the connectors is +300v! Perhaps checking the PSU out of the system
> isn't that good of an idea...
>
> Thanks again!
>
> -Jason
>
> -Jason
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Received on 2004-11-29 19:55:34