It's conversations and comments such as this that make me feel like an eager student at the Lyceum.😊

thats what i thought! the pass switch, "free wheeling" diode and inductor look like a standard buck converter to me. although the feedback and regulator circuit look very different from what I'd expect in a modern switching supply 🤔

I heard elevator music in the background while reading this :)

also could be that the unloaded output is actually whats causing the crowbar circuit to kick in

​@@juliankandlhofer7553That is what I thought. Everything is working as designed, but there is no load. I would want a headlight bulb on the output to see.

I'm just glad he had a camera pointing at it to capture the event.

every electrical component can emit light (and smoke), *At Least Once*

Goes with smoke-emitting diodes.

I've done it a few times - the biggest being a 10 ohm 50-watt resistor (I can still remember the foot-tall flame that shot out of it - 30+ years later! The things that happen as a rookie tech are easily seared into one's mind).

A wire wrap tool also works.

I was just watching that video this morning! Pure coincidence that we're both battling power supply problems, haha.

I really wanted an 11/60 back in the day, including when I was trying to start a computer school in the mid-80s. I had a lot of equipment for it, including SMP KL-10 pair from Intel and a 2065 from Columbia University. Then I developed inflammatory bowel disease, couldn't work, and lost everything in storage.

If the 11/60 wasn't limited to 18-bit addresses but had the 22-bit extensions from the 11/70 I think it would likely have been far more successful than it was. The microcode also could do all the floating point instructions if the FP hardware wasn't present. Over 40 years ago when I was working for DEC we investigated using the WCS option to create special instructions to handle some operating system functions unfortunately the performance gain was insufficient to take it into any product. Unfortunately I no longer have the microcode listings although I still have all the WCS manuals.

The 11/60 was, in effect, considered to be an enhanced 11/40 and the 11/70 was an enhanced 11/45. The 11/40 and 11/45 were really different classes of machine. In fact the head designer on the 11/60 also was the head designer the 11/40 (and the original 11/(20)). So the feature space we worked in was more limited than the one the 11/70 design team worked with. That’s one of the reasons for the difference in address space size. A microcode implementation of floating point might be faster than a regular software implementation but I doubt that it would come close to the hardware implementation performance. The FPU for the 11/60 ran asynchronously so you could be doing integer arithmetic (or anything else) at the same time the FP instruction was running. A microcode implementation would run inline with the program. Also there are cases in floating where the result is, in effect, unspecified. So any floating point implementation would have to be sure to produce the same unspecified results and the 11/40 did or it could end up breaking process control systems that used the PDP11. There wasn’t a formal instruction set for the PDP/11s, though at one point I think someone tried to document one. The key goal in implementing the 11/60 instruction set was to make sure that the 11/40 diagnostics would run on it (as best the could)and the 11/40 version of the operating systems ran on it. The 11/70 team had similar goals for 11/45 diagnostics. One big area of differences were in the setting of status bits that are set at the completion of an instruction. The diagnostics and operating system had dependencies on undocumented results in the status registers…each model set those bits differently (surprise, surprise). In some cases they used them to determine what model machine they were on. In some cases customer software made use of undocumented status (and other) results too. I had to insure that the 11/60 set the same undocumented values in the status registers as the 11/40 did… did I mention that those settings were undocumented :-). The 11/60 had a one-way associative cache and the 11/70 had a two-way associative cache. In practice I don’t think the 11/70 ended up with a better hit ratio than the 11/60. The 11/60 and 11/70 were the first cache machines for DEC. Needless to say the cache did a number on the existing memory diagnostics… so they had to be updated. Oh hum, things I haven’t thought about in five decades.@@jeremybarker7577

@@dansullivan6787 Thanks for that additional information Dan. The work I did dates back to 1978 so like you it's a long time ago to remember.

I think it needs a load too.

Squueze it, squeeeeeze it! Tighten those buns ladies!

An official DEC power cord, no less! Subtle flex. 😂

Switch mode vacuum tube power supply, that'd be "cool" 😂

Thank you! That old Weller is awesome! Everything I'm doing could totally be done on a much cheaper, older analog scope too. I just use the digital job when filming so I can take scope shots mostly.

If you go into a professional electronics repair workshop, you'd probably be shocked just how old and apparently low-spec the test gear is! Quite often, when hobbyists get into electronics, it turns into a Pokemon collect-all-the-gear hobby, where people are convinced they need a 4 channel, 10GSPS smart scope and a 7.5 digit meter.

Nothing a screwdriver can't fix! At least that's what I told the doctor, but he just said "Nah man, you crazy."

The red and green transistors are ancient General Electric parts. D44xx were quite popular many years ago. That is the full part number. They are not 2SDxxx Japanese parts. The D44C8 is still being made by ON Semi.

He had high watt load resistors on the power supply at one point in the video. The LM7805 is a linear type regulator, used for the 5v rail and it doesn't require a minimum load as the internal draw of the IC (2-3ma from memory) is sufficient. If I recall the 485 has a switching style power supply not a linear system.

@@user-uz1yv2oc9v The 5 volt supply is also a buck converter, just using a three-terminal linear regulator pressed into duty as the controller for switching.

Lamps or ceramic resistors are a great test load. Both keep the bench warm and cozy.

If you put in a modern PSU and emulate the drives, you may as well emulate the whole computer with a Pi. It takes all the fun out of vintage computers. 👍

I don't think anyone should get in to this hobby if they aren't willing to restore and use original equipment wherever possible. Emulated drives are good for hobby reproduction systems... or if you can't find the right drive/media. Neither of the things you mentioned would be unreversible though... so not too bad.

​@@maskddingo1779the original drives are aging and in far more limited supply than the actual systems they serve. Emulated storage isn't just convenient, it also saves you from repeatedly cycling an aging drive while diagnosing for example. I think a restorer with emulated drives is just smart. If you can keep an original working that's great, but using emulation saves it from wear and tear.

​@@maskddingo1779also power supplies in the past did not always have the greatest protection circuits. If they had them at all. Using a modern well protected power supply, might be less original, but it protects your machine from being blown up because of power supply failure. And failure becomes ever more likely with age. Even curious Marc recently had a video where he added a crowbar circuit to a vintage power supply that had broken and killed the computer attached because it did not have a crowbar circuit. Something HP added to later models. Original no, safe yes.

@@bzuidgeest Has UE said what drives were in / were avalible to this system at new (late 1980 to me isnt that long ago)

odd that once fuse replaced everything sort of worked as it should (I assume circuit and drive draws finally blew the old one)

To be honest, I wouldn’t apply mains to something this old without replacing electrolytics outright. Call me overcautious but there were two, ahem, “excursions” in this video and there is simply no future in going forward with 40-year-old electrolytics even if they appear to hold back DC.

@@hubbsllc Yes there is a good argument for that, especially considering how much it could damage if that 5V turned into a 12v supply. However I suspect the old Western electrolytes are longer lasting than the new ones. With the old ones you would only have a problem if they were in close proximity to the places where they could get hot, so pull out some of the best suspects and test them to get an idea what the rest are like. The thing is, with a fuse like that I'd see it more likely one of the power transistors has failed, and sometime that takes out a driver transistor. Sometimes they can half fail so you have a leakage across the junctions. It's better to spend 20m checking all this before applying power as well.

@@Andrew-rc3vh Yes - a blown fuse (especially if it had been checked from the get-go) is a good indication that something already went awry so you know there has already been an overcurrent event. Those electrolytics can appear to hold a voltage but in the case of filter caps they're expected to experience AC current - not exactly the conditions of that test. And on top of that they may appear to hold voltage *now* but what about after 15 minutes in an energized circuit? This does imply that if you're going to entertain getting a machine like this running and keep it running, there's a certain cost/effort to sink into it before you even give it mains which is why you need to be clear about what your goal with a piece is and how committed you are before you even put it on the bench. I restored a 1954 tape recorder and started by rebuilding the whole power supply onto a perf board; a dual-element power resistor had one leg that was open-circuit and there were two can caps that I removed outright. I didn't even plug the power cord in until that much was done.

Absolutely! Except, I didn't have a spare, so instead of waiting on parts to arrive, I figured I'd take a stab at repairing it so I could continue on with the build. I'll order up some replacements and fix it properly once I know for sure the PSU is going to come back to life.

It was a very clever solution to an immediate problem. And if it works, it works.

Thats obvious of course it would have been simpler I bet he wishes you were there to tell him that....oh wait a minute he didn't have one.

Don't mind me I'm grumpy :)@tradde11

Have you considered donating extra storage, every cost, budget, time and whatnot😃. He already stated he has a limited supply of all those things.

@@bzuidgeest there is probably not even time to read up on what everyone is doing with the PDP items that were passed on to others !. UE multi tasking here even with the automated circuit board/s being made up at same time !

... Especially once they've been used as light emitting resistors... LOL