LisaList2

Hello and many Thanks for the infomation!

Back to the unusual frequency- could it be possible that it had something to do with the US TV Colour norm-even if the Lisa has no colour capabilities, the Lisa has a Cinch connector for external Monitors. The B&W composite signal should have no colour carrier, sometimes there is one, some surveillance  VTR's need that carrier for switching the automatic recording on and off - the NTSC colour carrier is at 3.58 MHz and sometimes at 4.43 MHz- could there be a sort of  a colour trap for avoiding cross color effects?
It's only a thought, because I'm working with old open reel and cassette VTR machines and TBC's
I just found another source for a suitable Quarz oscillator:

https://centuriontech.eu/product/customized_oscillator/

Is this a good company?

That's my guess too --- I'd expect that Widgets weren't exactly ready for production when this bezel was made.

The Lisa 2 designers may have found a need for more vents, but the Lisa 2 vent style may also a better match for the design language of contemporary Apple products, I think. This prototype bezel is like a glimpse of what the Lisa 2 might have been if Snow White had never happened. See also Wikipedia, for what that's worth.

I bet that was used with the internal mount ProFiles...

-J

This really is incredible. New discoveries like this are rare.

The panel couldn't have been made after the decision to give the Lisa 2 series Sony drives like the Macintosh, which places it before Late 1983. Given this could have been for either an internal Profile or Widget drive, that leaves some wiggle room for when this could have been produced. Maybe this was a Lisa "1/10" panel?


Obviously, the engineers realized they needed much more ventilation for the hard drive than what this panel has.

CR21 had a big crack and burn hole in the side. Clearly something else is wrong somewhere "up the chain". I have a couple more MPU131s at least, but clearly I need to do some more investigating around the schematic.

Patrick has an excellent strategy for troubleshooting this PSU in another topic:

disconnect mains, apply +5 V from a lab PSU to the +5 V rail and -12 V to the-12 V rail. Do not apply -5 V to the 7905 output, these don't like to be reverse-powered. Put an 1k resistor in series with the +12 V rail and apply 12 V. The resistor is necessary to limit the current through CR21 when it fires.

Now start with R29 away the Q4 side. Rotate it slowly and see what happens with Q3 and Q2. The voltage at the base of Q3 should rise until it reaches 0.7 V. Then Q3 and Q2 should conduct and the PUT triggers. That means the voltage at pin 3 goes from 12 V to almost zero.

If this works, connect another 1k resistor from pin 3 of CR17 to 12 V line. It might be necessary to disconnect pin 3 from the PCB, so that only the bias voltage is connected. Now repeat the procedure above and check if CR17 triggers, too. Your fault is likely to be somwhere in this area.

The only PUT you can buy today is the 2N6027 from OnSemi. This works as a replacement for the obsolete MPU-131.

where can I get these "special" Quarz oscillator, running not at 5MHz, but at an unusual frequency of 20.37504 MHz ? AFAIK only Lisa used this frequency- why is this necesary- can I run it with exactly 20.0000 MHz?

Yes, as far as I know, you can use a 20 MHz oscillator. Decades ago I installed a 20 MHz crystal to repair a CPU board and AFAIK there were no issues.

I haven't figured out why Apple chose the unusual frequency... does anyone else know or have a probable explanation?

Now that there are "programmable" oscillators, some suppliers will program an oscillator to the frequency that you request, and 20.37504 MHz is no more difficult than 20.00000 MHz.

Looking at what DigiKey has today, choices for a 5V, TTL output, through hole programmable oscillator lead you to a selection of EPSON SGR-8002 parts. The board accepts both "full size" and "half size" oscillators.

Either the Standby or Enable control version will work as the control pin is grounded on that board. Either commercial or industrial temperature range is sufficient, and for this purpose 50PPM or 100PPM accuracy is irrelevant.

Picking one of the options, eg. https://www.digikey.com/en/products/detail/epson/SGR-8002DC-PTB/755251 it says it is a "value added item" which means that you should disregard the stock level of 0 as they make them to order. It says "Enter your frequency in Web Order Notes" so add something like "program SGR-8002DC to 20.37504 MHz". The programming is included in the price and is done within a day in my experience.

Note that the programmable oscillators require a special programmer (ie. not an EPROM programmer), and typically can be programmed only twice (they can't be erased and reprogrammed many times the way a UV EPROM can).

Truly remarkable find. Under the floorboard in a closet, no less! I don't think this front bezel has ever been seen publicly before. The design seems a little hasty and awkward, with the upper drive number and space for its eject button remaining in place next to the vent. That should have been removed

Was this bezel for a prototype Lisa 2/10 with an internal ProFile (Pepsi) or Widget drive paired with a single Twiggy drive? Interesting configuration.

Hey all. Someone posted this to one of the facebook groups tonight: "Good evening group! Does anyone know what kind of Apple computer this is? I bought a home in Albuquerque, NM from a man who was an original apple employee in Cupertino (I found his ID) and I found this under a false floor panel in a closet. Very "Sherlock 😂" I know, but it's a true story. Anyway, just wondering.."

Seems to be two Twiggy based Lisa 2 proto front panels and a complete Lisa 2. Has anyone seen one of these before?

 

(I know this thread's pretty old, but I wanted to post an update after I finally got around to taking a look)
I ordered a couple new-old-stock MPU131s from here: https://smallbear-electronics.mybigcommerce.com/transistor-mpu131-programmable-unijunction/
I soldered it in to my PSU, put it in the Lisa, put the back cover on (engaging the interlock switches), and connected the power cord. Before I even pressed the power button, I could hear a crackling noise and saw some magic smoke come out the side.
I took the PSU back apart, and sure enough, the new MPU131 I'd put in at CR21 had a big crack and burn hole in the side. Clearly something else is wrong somewhere "up the chain". I have a couple more MPU131s at least, but clearly I need to do some more investigating around the schematic.

Lisa has an internal monitor, so you don't have to take care of any video timing. Serial communication will be 2% too slow, but this should be acceptable.

All files for the Lisa ROMs are at bitsavers.org. You only have to buy the video state PROM from vintagemicros.