LISA PS TESTing

[anotherLISAguy]

I guess recently ran a search on this board related to this but I wasn't getting any hits so I'm going to reach out and see if people can recall what it is I think I saw.

It related largely to being able to take a Lisa power supply put it on your bench put a pen or some non electrical item into engage the soft switch and then with the use of I think a resistor between two pins you are able to plug in the power supply and energize it and then you'd be able to read power levels off of different pins kind of a test bench sanity check.

Of course this all may have been wishful thinking or the passive dreams of a senior citizen cross pollinating some other power supply testing ritual but I seem to think that it's true and it made me think in talking to another member that that would probably beg for a very good bread boarded card to build something that the user would be able to take a power supply slide it over the cart edge connector Set the read switch apply power and then press a button to energize it and get some type of 12 or 5 Volt status light lit up to let you know that the system is live and then the exposed finger safe pin out pads to probe and get some sanity numbers from. If such a tool was available I think it would be worth a few coin to have in their arsenal particularly when they can avoid having to resuscitate a dedicated machine if they so happen not to have one. ahem

So if anybody can tell me if I'm dreaming or delusional about this impromptu test procedure, I'd appreciate it likewise I'm sure anybody else found in that similar dilemma would be interested in hearing about the idea of being able to do such a thing and create such a simple PC board. With a nice 3D printed snap on enclosure all those things would make it really sexy too. Just me and my early second cup of coffee thinking anyway if somebody has some input on this I'd appreciate hearing from it and I'm sure so would any one else who has said Gee I wonder if this power supply is any good.

Thanks in advance for your input and guidance and as always LISA ON!

[stepleton]

It's a perfectly achievable thing to do. I have a wad of resistors and thick wires attached to a PSU connector that I use for occasional PSU testing. I call it the Lisa 0. To turn on the PSU, you short a particular PSU pin to +5V Standby if memory serves. These contacts are on opposite sides of the edge connector, so even without this gizmo you can do it with a crocodile clip if you want.

Two thoughts:

First, the Lisa hardware manual indicates lower and upper bounds for current draw on each power rail. This suggests that before you take measurements of your PSU's performance, you ought to have an appropriate load (i.e. resistor) on each rail in order to place the PSU in a condition that adequately simulates ordinary usage. It's possible that the PSU may not run at all without a load on at least some rails. Whether that's the case may vary between the original Apple PSU and the Datapower PSU that was supplied with the 2/10.

Second, the Lisa PSU puts out plenty of power, appropriately enough. You will need to use hefty power resistors if you are running the PSU for longer than a very brief time, and even then you will have to find something to do with all of the heat. When in use, parts of my Lisa 0 become too hot to touch pretty quickly, so I never leave it running for very long. Consult resistor datasheets for power ratings before choosing your parts, and if you want to stress test a PSU for longer, you are probably better off using a bench electronic load or some similar piece of equipment that can cool itself. This doesn't have to be outrageously expensive (though it certainly can be if you want): you can buy a handful of pretty cheap loads on AliExpress that will do the job if you don't mind the risk associated with, well, very cheap things.

[anotherLISAguy]

Hey thanks for charming in I just happened to peek in and see if anybody had any input on it I do recall that there was somebody who had an article on temporary powering on and a resistor as you said is what you used.

I don't think that the anticipated use would be a hell of a lot just enough to get a decent read - in my head I kind of imagine that edge connector plugging with that push button - While I fancily imagine this device why not put in some digital readouts to get numbers - inside of a minute you could get a health check with nothing more than the grandchild of your LISA O card, a power cord and a plastic doohickey to set the Reed switch. 

I'll have to do a better job of scouring the Lisa list it might have been LISALIST 1 to find that magic combo - Like I said at least you're validating that I wasn't imagining things even if my plug and play testing doesn't exist it sounds like it could easily enough - thanks for the info hopefully somebody else can say "I remember that article and have a copy of the thread" or whatever. 

Either way with the information, I can somewhat confidently old school the ps check while fantasizing about my plug and play device .

Again take care and LISA ON!

[TorZidan]

To complement stepleton's answer above, here is his "Lisa 0": https://68kmla.org/bb/threads/finally-manged-to-acquire-a-lisa-2.43744/post-477609

I am hesitant to post a photo of mine, as it looks much more ugly. I used hot glue on my resistors, and it starts melting if I keep the PSU running for more than 30 seconds. What was I thinking!

IIRC, the 1.2A PSU is much more sensitive about loads on each rail, so you need all the resistors on the picture. The 1.8A PSU may work with fewer resistors.

[patrick]

I don't think that the anticipated use would be a hell of a lot just enough to get a decent read - in my head I kind of imagine that edge connector plugging with that push button - While I fancily imagine this device why not put in some digital readouts to get numbers - inside of a minute you could get a health check with nothing more than the grandchild of your LISA O card, a power cord and a plastic doohickey to set the Reed switch. 

To operate the PSU, you need some minimum loads on the supply rails. At least 3-4 A at +5 V and 0.5 A at +12 V. An old spare bulb box from a car or a set of power resistors would be suitable for this.

Without a load at +12 V the crowbar will trigger and shutdown the PSU. You will hear a ticking sound.

Connect +5 Vsense (pin N) to +5 V and ON (pin X) to +5 Vstby (pin 20).

[stepleton]

To complement stepleton's answer above

Ha, thanks! I'm so disorganised with my photos that I basically gave up on finding that one before I started.

Once a friend and I were in a "what's getting hot?" bind while diagnosing a PSU without having a thermal camera handy. We had a suspicion of the culprit but didn't want to touch the part to confirm it. So we poked it with a hot glue stick and sure enough! And given how fast it melted we were glad not to have tried a finger first.