PDP-11/03 Recommended Maintenance?

[emoore]

Hello, I have had my PDP-11/03 for about 5 years and love it to death. I am about to get an H11 so going to brush back off the PDP since they are board compatible.

I have never done any maintenance on the PDP beyond some canned air and re-seating boards. I am okay with a soldering iron, but have never desoldered an old board or anything to replace caps.

Can anyone recommend what preventative maintenance I should do? Anyone in the Austin, TX area who would be willing to maybe help me out getting started? I also need to clean and align my RL02 as it has some weird write issues on one of the two sides.

Thanks for any help!

[saipan59]

Others will probably give better specifics, but my thoughts are:
- Focus on the disk drive(s), if you plan to keep using them. Anything with moving parts is at risk. Rubber belts/pulleys, bearings, lubrication, cleaning.
- These hobbyist/collector machines are usually treated much better than 40 years ago, so that's good.
- Keep the ambient temperature low-ish whenever possible - heat degrades lots of things, and leads to component failures. Consider adding more/better air circulation that what is technically required.

Pete

[saipan59]

One more thought:
To maximize the life of vintage gear, it *might* be a good plan to run it on slightly reduced AC power, to reduce stress on various components (especially the power supplies).
You can do it (for example) like this: Build an AC box that is dedicated to your 11/03. Inside the box, mount a good-sized 6.3V "filament transformer", and connect it to "buck" the line voltage, giving you an output that is 6.3V less than normal. I can elaborate if you really want to do this.

I'd be interested in hearing comments on the possible pros/cons of doing this with old computer gear. I've done it with a vintage radio receiver that is valuable, and full of "unobtanium" parts. I used one of those packaged auto-transformers that was made for use in TV/Radio Servicing in the old days.

Pete

[bqt]

I also need to clean and align my RL02 as it has some weird write issues on one of the two sides.

Thanks for any help!

RL drives don't need any alignment. They are self aligning drives. The only potential benefit of any type of alignment is that you might have a faster switch between the heads, as the heads might need to move some to lock on the track of the opposite side if the two heads are not aligned relative to each other. But that only cause a speed issue, and nothing else.

If you think you have some problem with a drive or disk, it is something else than alignment that is the issue.

[glitch]

Reducing line voltage isn't likely to make a difference, especially on a PDP-11/03. If something fails at our slightly higher modern levels, it was on the way out anyhow!

[Al Kossow]

Reducing line voltage isn't likely to make a difference

It seems like a really bad idea with switch-mode power supplies. You're just going to increase the current in the input chopper.

I could see making sure you have clean AC power to minimize brownouts, and short-term line dropouts, but I wouldn't lower it
by some arbitrary amount

[saipan59]

It seems like a really bad idea with switch-mode power supplies. You're just going to increase the current in the input chopper.

I could see making sure you have clean AC power to minimize brownouts, and short-term line dropouts, but I wouldn't lower it
by some arbitrary amount

Ah, good point about switch-mode supplies. I hadn't thought of that angle.
Perhaps the idea still has merit for gear that has a linear PS. For the 'special' radio that I mentioned, it is all linear, and a hybrid of tubes and early transistors (design circa 1959). Most of the tubes are inside little sealed modules, making repair difficult.

Pete

[glitch]

Reducing voltage on a linear supply *can* result in reduced heat from regulators and diodes. Sometimes I turn the line voltage down a little if I'm working with my IMSAI, have very few boards installed, and have a board up above the card cage that tends to run hot anyway -- otherwise I get to point a desk fan at the board. But, for the majority of PDP-11s, that's not relevant.

[KC9UDX]

Reducing line voltage makes sense on very old gear. A lot of it was designed for 110VAC or 115VAC. Old Zenith receivers are notorious for this, the power transformers have no margin of safety, so they burn up (literally) when powered up at 125VAC.

But as mentioned, this isn't suitable or even safe in all situations.

[MauriceH]

Reduce supply voltage is safe to look for a Voltage Stabiliser transformer.
It is a transformer that with in reason will out put fi.i 220V regardless off the input.

Than keep the machine clean, press buttons with care.
Don't keep turning it on and off in short times.

Capacitors are know to be of good products in those old machines.
If you plan to change them, look at the spec's for lifetime prediction.
Often it is only 5000h or 10.000h.
Try better ones like 100.000h and low ESR with 105C.

BUT fiddeling on the cards to swap components is to be at a minimum.
The solder pads could be damage at the wrong handling or you will f.i. damage the throughput buses.
If a IC has to be changed use a good type of IC holder first.
Don't try to solder out the complete IC at once but cut all the wires from the defected and solder out one by one.
Than clean the pad with desolderbread, put in the IC holder first than the new IC.

So repair when needed.