Pcb on Symbolics LISP Engineering

XL1201 Merlin II Chip Reseating

Sun, 24 Jul 2016 19:48:20 +0000

UPDATE: I clipped and removed the broken capacitor. Replacing it will be the task of another day.

I spent two days removing, cleaning and reseating each DIP chip on the Symbolics XL1201 Merlin II Main (CPU) board. Earlier I closely examined the solder side of the board and found a few minor discrepancies. This time I also encountered three discrepancies:

Bent pin on chip BB27 - unbent
Broken bypass cap next to chip GG7 - I clipped this one off entirely and will replace another day
One long bodge wire running along the entire top has come loose. This could get snagged on something and fall off.

Additionally, I removed and resocketed the Weitek Floating Point co-processor without doing any cleaning. It looked sparkling clean.

Detailed Inspection of XL1201 Merlin II Solder Side

Sat, 23 Jul 2016 19:18:35 +0000

To see if I can isolate the cause of the XL1201 instability, I am going to physically inspect the two main cards with a loupe and flashlight. If I see anything suspect, I’ll take a picture with a (cheap) USB microscope.

I am doing a detailed inspection of the solder side of the Merlin II CPU card first.

Overview picture:

Discrepancies

There are only two that are concerning to me, but several others were found. The two of most concern are:

Console Internals

Sat, 25 Jun 2016 18:09:57 +0000

This is a Symbolics Model PE36-PCONS, Part No 365404 Rev C console. My serial number is 21811. (“There are many like it, but this one is mine.”) An album of detailed internal photographs is available including full size versions of all the below images.

The console seems to be in good shape, with all electrolytic capacitors intact (not bulging or leaking). I should probably test the power supply outputs as there are trimmers for the voltages to adjust them.

Broken SCSI Pin on XL1201

Fri, 24 Jun 2016 00:03:00 +0000

Well, I was installing a new hard drive into the XL1201 today and just before I connected the SCSI cable, I noticed a pin seemed to be missing on the 50-pin SCSI male connector on the backplane. On closer inspection, it’s definitely missing.

Fortunately, it seems to be pin 1, which is a Ground pin on both single-ended and differential SCSI. Since half the pins are ground on single-ended SCSI, that’s fine, and there are still quite a few ground pins on differential, so we’re fine. It’s the bottom left pin in the picture here.

Console Monitor Adjustment

Sat, 18 Jun 2016 15:49:39 +0000

There are 10 controls for monitor adjustment. Two large finger controls, a group of 6 small multi-turn trim controls for vertical, and a group of 2 small multi-turn trim controls for horizontal.

You can access these controls by unscrewing the four screws at the back of the monitor and sliding out the rear panel. They will be at the right side (looking at it facing the screen).

I’m not sure what exactly all of these do, and don’t have any manuals about them, so if anyone knows what they do I’d welcome the information. (Try me using symbolics at the last two parts of the domain name of this site.)