Solder Problems (PDP-8/m related)

From: Zane H. Healy <>
Date: Wed Dec 1 14:41:13 1999

OK, I confess it's been almost a day since I worked on my PDP-8/m. I
discovered that I appear to have, what looks to me at least to be, a very
serious problem. I thought that one of the LED's for showing the address
was out, been that way for at least a couple days. Then yesterday morning
I put it on the table I've been using when I'm working on it, and another
LED was out. Another address LED, but the one for the second bit, in other
words set it to address 0002 and it looks like you're at 0000, grrrr!

So I pulled the front off and discovered that the solder connections have
apparently gone bad. I reheated the solder, and added a little. That
fixed it for shortly longer than it took to get the front back on. The two
LEDs are back out.

Even more frustrating, checking out E46 on the G227 with my new TDS-220
Oscilliscope it looks as if everything is just fine. Yet the other day
when I checked it with the logic probe it wasn't (still have the same
problems with memory though). Probably better explain this, I'm seeing
'pulses' on the outputs that correspond to those on the E39 chip, in other
words one chip is doing the xxx0 - xxx3 and the other the xxx4 - xxx7,
which I wasn't seeing before. Still I really should recheck the results
with both the Logic Probe, AND the Oscilliscope.

So, I'm starting to wonder if I don't have some fairly serious problems
with the solder joints in this system. What is the best way to check for
this, and fix any problems that I find.

In any case I obviously need to get a decent soldering iron, the el-cheapo
Radio Shack one I've got is as old as some of the parts in the PDP-8! If
nothing else I need a decent tip.

| Zane H. Healy | UNIX Systems Adminstrator |
| (primary) | Linux Enthusiast |
| (alternate) | Classic Computer Collector |
| Empire of the Petal Throne and Traveller Role Playing, |
| and Zane's Computer Museum. |
| |
Received on Wed Dec 01 1999 - 14:41:13 GMT

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