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[ried]

Update: Solved. If a LisaDAC expansion card is located in slot 1, error 47 appears upon cold boot when the new PSU is in the machine. If the LisaDAC card is relocated to slot 3, there is no error.

Someone in the community is producing a new Apple Lisa power supply, using new all new case materials and components. I purchased a unit from the initial run and have been testing it in a few Lisa configurations including the Lisa 2/5, 2/10 and Macintosh XL.

Upon cold start, the Macintosh XL gives an Error 47 at the end of its power-on self-test. It gives the option to restart and, when I do, it runs through the POST once again and no error appears. Error 47 only appears upon cold start in the Macintosh XL. Any idea what it could be flagging? Is it testing something in the 3A/88 ROMs that might not be present in H/A8 or H/88?

Again, the Lisa 2/5 and 2/10 are not showing the error with this PSU under any conditions. Returning the original PSU to the Macintosh XL resolves the error.

Gallery: https://imgur.com/a/DaSnn0M








And the error in the Macintosh XL:

[ried]

In case it matters, the Macintosh XL features an original 16MHz XLerator with SCSI, PFG, X/ProFile, etc. Again, no errors at all with the original PSU. With the new PSU, error 47 appears with a cold start only, and does not appear during a restart. After error 47 appears, I can also choose "Startup from..." and boot normally with no issues.

[anotherLISAguy]

Did you have a look through the board designers notes.
The layout looks identical to the LisATX - Pico ATX PSU Replacement
https://github.com/warmech/lisa-hardware/tree/main/LisATX%20-%20Pico%20ATX%20PSU%20Replacement

Looks like they went to the trouble to do the branding and toughened up a couple of spot.
Do you have a link to the reseller.
Had considered building my own (all the plans are there)

Keep us posted as I am sure others would find an alternate PS a great base unit to bench with.

As for a late thought on the issue, since it goes through everything and at the end 47s you - a semi-educated guess would be some added code/reliance added to the XL ROM (assuming all other things equal)
whether the 'original 16MHz XLerator with SCSI, PFG, X/ProFile, etc' are adding any additional checks/flags is another

[stepleton]

Silly question but does your PSU replacement provide a reliable +5V standby power? I'm wondering if your RTC and parameter RAM are taking on random/invalid values each time you restore power after turning the machine off.

A different but very related question: do you find that the Error 47 occurs with an original PSU after you unplug the Lisa and plug it back in?

[AlexTheCat123]

It might also be worth trying things without the XLerator and PFG to see if that helps at all.

[ried]

Silly question but does your PSU replacement provide a reliable +5V standby power? I'm wondering if your RTC and parameter RAM are taking on random/invalid values each time you restore power after turning the machine off.

A different but very related question: do you find that the Error 47 occurs with an original PSU after you unplug the Lisa and plug it back in?

It does provide reliable power that keeps the time, startup disk settings, etc. Unless you use its built-in power switch - in which case it cuts power to the machine entirely (resetting the time).

Error 47 never appears with the original PSU under any circumstances.

James M. kindly suggested that Error 47 could indicate a malfunction, and that the +5v rail could be drooping below spec during the cold boot and generating the error. He suggested removing one of the memory boards to see if that helped. While I was in there, I removed both the secondary memory board (a 1.5MB RamStak) and the LisaDAC. I can confirm with certainty that the LisaDAC is causing the issue. Removing it resolves Error 47 with the new PSU entirely.

So, to my untrained eye, it seems the LisaDAC is just a little too power hungry for the new PSU. Everything else including the XLerator with SCSI, PFG, Parallel card, X/ProFile, and 512K Apple RAM + 1.5MB RamStak function just fine when used with the new PSU. Add the LisaDAC, however, and we get Error 47 on cold boot. Choosing "Restart" and ignoring the error by choosing "Startup from..." allow the Lisa to continue without issue, but it seems that Error 47 is inevitable with the LisaDAC installed.

I shall put the original PSU back into this particular machine.

[sigma7]

... added code/reliance added to the XL ROM (assuming all other things equal)
whether the 'original 16MHz XLerator with SCSI, PFG, X/ProFile, etc' are adding any additional checks/flags

None of these bits of hardware add or alter code to be executed per se.

The 16 MHz XLerator does affect the timing of ROM code, which causes error 42 (with non 3A ROMs) due to it not being able to read the serial number. The 12.5/18 MHz XLerator design doesn't affect the timing as much.

[sigma7]

I can confirm with certainty that the LisaDAC is causing the issue. Removing it resolves Error 47 with the new PSU entirely.

The LisaDAC isn't particularly power hungry, so that's pretty mysterious to me, especially since you reduced the overall load otherwise. Did you try moving it to another slot?

Looking at the SETVCTRS routing in the ROM listing, it looks like all of the unusual/unexpected "exceptions" result in error 47, which means all of them except:

• $08 Bus Error
• $0C Address Error
• $10 Illegal Instruction
• $28 A-Trap
• $2C F-Trap
• $7C NMI

Others would include
Divide by Zero
CHK instruction
FTraps (other than the F-Trap emulator)
Other unanticipated interrupts
... and more!

So error 47 means something went wrong in an obscure way, such as fetching an instruction resulted in something garbled that didn't execute correctly.

The LisaDAC does use an interrupt, but I think that isn't enabled until the software loads the LisaDAC; ie. well into booting MW+/II.

[ried]

Well, I'll be a monkey's uncle Sigma7 is right again. Moving the LisaDAC from expansion slot 1 to 3 resolves the Error 47 issue. The new PSU is now working as normal in the Macintosh XL. Thank you, James.

I do not know why the original PSU was fine with the LisaDAC being in slot 1, but the new PSU requires it to be in slot 3. Such is the mystery of vintage computing.

Now that this issue has been resolved, I will continue testing this new PSU and report back with any additional issues that may arise. So far, it appears to be a solid alternative to the original.