Power on Symbolics LISP Engineering

XL1201 Stability Update

Sat, 16 Jul 2016 15:47:51 +0000

In an effort to rule out the power supply causing the XL1201’s instability, I sent it out for overhaul by Power Clinic. After reinstalling it, I booted the XL1201 and just let it sit in the Document Examiner.

Unfortunately, the computer decided to reboot itself after about 15-16 minutes. So, the power supply would seem not to be the problem.

I will have to disassemble the XL1201 and give it a thorough examination to see if there are any obvious physical defects. If none are found, I will try to remove, clean, and reseat all socketed chips, and see if that helps.

Todd MAX-354-1252 Power Supply for XL1201

Wed, 13 Jul 2016 23:28:33 +0000

So, I learned something about the Todd MAX-354-1252 power supply in the Symbolics XL1201 today that I thought I’d share. Not that I understand it, mind you.

The power supply has six trim pots. Four are obviously labeled for adjusting the four output voltages:

5V at 50A
12V at 8A, 12A peak
-12V at 2A
-5.2V at 10A (for ECL circuits)

However, according to the expert engineers at Power Clinic “The two [remaining] trim pots in question are related to the front-end boost circuits. One is for operation frequency and the other is for boost fold. NEITHER should ever be adjusted.”

Power Supply, Memory, Crashes

Tue, 05 Jul 2016 04:03:54 +0000

I don’t have the time to post all the details before going to sleep, but I did a few things tonight including measure the power supply voltages, install new RAM, and have a lot of problems and crashes.

XL1201 Power Supply Voltages

I tested the voltages of the XL1201 power supply with a Fluke 269 multimeter and a Rigol DS1000E, while the system was on and sitting at the FEP command prompt.

XL1201 Power Consumption

Sun, 26 Jun 2016 21:32:29 +0000

I was asked how much power is used by the XL1201. Here are a few data points…

XL1201 with only SCSI2SD: 222-233W
Console: 106W

With the XL1201 sitting idle it takes the same amount as calculating (fib 36), so apparently the CPU is running at a constant speed at all times.

When the console goes into sleep mode (after 20 minutes by default), power usage doesn’t appreciably drop.

Console sleep mode: 105W

With the XL1201 running a 15,000 RPM Seagate Cheetah X15 drive (ST318451LW), it doesn’t really take all that much more power.