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- čas přidán 18. 08. 2024
- Episode 767
Another Craigslist find. This time a classic Harrison HP Power supply. 200W version 0-20V and 0-10A. I test it and find a fault. It's missing some knobs too. Seems like the only thing wrong is the meter. I will try to repair that with out breaking it.
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"A supply so nice I fixed it twice." :) Well done...both times.
"Hand Drawn" Schematic, and also a "Hand Taped" PCB! So beautiful...
"Doctor! Doctor! The needle stops moving when I press it!" "Don't press it!" Nice repair! Love the "handmade" stuff!
those old Harrison/HP supplies are the art of psu design 101, still amazing 40-50 years later, 200uV ripple...just amazing
the video is repeating at 9:00
Oops. Edit fail.
Swear to God I thought I was stroking out!
I have the HP 6286A and the 6291A (0 to 20V and 0 to 10A). I bought both from ebay. I"ve never done a thing to them except use them. I've used the remote sense and the other features and they work great. Thank you for this very insightful and entertaining video! Your SCR explanation was excellent.
Excellent repair IMSAI Guy! I thought I was having a deja vu moment @ 9:05, but then I came to the realization that you were just trying to make sure we understood how difficult it would be to obtain a replacement device for the dual device matched transistor pair... Fred
Great close up photography. Had a similar problem with a HP 427A. Disassembled meter as you did and found using some good contact cleaner did the job. Believe with time the contacts inside meter get a little dirty like switches and pots on old radios. Anyway it worked, no more intermittent operation. Love that print! Thanks Sherman.BTW, jumped ahead because of repeat in video, to much coffee before upload or trying to keep us on our toes.
very different SCR regulated PS. nicely explained.
I am a big fan of those Harrison bench power supplies. My 6236B is one of the most reliable pieces of gear I have, and is older than I am; it's perfect except for the unobtainium lamp which I am afraid of altering the circuit in any way to replace with something else. Not critical.
They are truly a joy. Somewhere on the web is the history of the Harrison supplies, which looked identical before the buyout except for the HP badge (love the vintage HP badge). In the history, which I can't find anymore, is an HP tech who reported that the rest of the HP techs _intensely disliked_ servicing the Harrison supplies, because their design was dark magic at the time. Technology and fabrication caught up eventually, but the Harrison Labs techs are unsung masters, apparently.
Great Job. Love the nostalgia with the schematic. Really good deal for $40 and a little work. Thank you for sharing.
5:30 S.C.R Control flavors the output voltage of your power supply with the piquant harmonics of switching semiconductors, for the best and most unique precision measurements!
Harrisons are very nice power supplies and far more rugged & reliable than contemporary supplies.
Yes, current goes through the top and bottom hair-springs to reach the coil.
Next time the meter acts up, and it probably will, drive it with a low voltage rather than from a constant current supply.
Any fluctuation in contact resistance will be evident from a voltage source but compensated for by a CC supply
making it difficult to locate. Digital multimeters on the ohm ranges often output 1-mA which would be just about right. You can also watch the resistance fluctuate on the digital display. The screw heads on the back of the meter case will allow the magnet assembly to be removed. When you have it out, tighten all the screws / nuts that the current goes through. The meter is acting as if there is a loose connection. That poor connection will never improve.
If you eventually pull the meter and tighten the hardware, before you put it back in, balance the movement and set the zero position. Good Luck
Great video..... Great video... in case you missed it the first time.
I really liked your video. Fun project. It's really nice when problems aren't too daunting. Thanks. It is appreciated.
I like all HP test equipment. Great repair sir
These videos are awesome...! You should have many more subscribers for sure.....but I guess you have Quality over Quantity right now! :-) Keep it up....this old EET really enjoys your skill set....
Great fix! Messing around with the guts of an analogue meter is scary. One slip.........
You need to do a load test at high current. I have several of these, one of which falls out of regulation under load. I decided not to fix it, but use it for parts. The meter bezel plastic is fragile and becomes brittle with age. Otherwise, it's a great boat anchor PS that uses phase firing of SCR's for control. Doesn't quit fit in as a truly linear power supply. All of mine make a nice buzz under load....it's normal I think.
I did a load test in part 1
Good fix, at least for now. I suppose if that meter keeps acting up one could cut out a rectangle of aluminum to fill that square meter hole and then install a digital panel meter of some kind. Wouldn't look "vintage" but might be a bit more accurate.
Nice job! Those meter movements can make you question your career choice if you dive too deep. Glad it wasn't anything major.
Nice fix on the meter...not sure I would have been as brave! ;-)
i have a power supply that uses scr pre regulation too but instead of a half controlled bridge rectifier, it uses anti- parallel thyristors(essentially a triac dimmer circuit) to phase angle control the primary side of the main transformer. im not sure y they did one and not the other maybe the non sinusoidal wave causes harmonics in the transformer and causes noise but the higher voltage means lower currents for the thyristors. but the control board was missing and figuring out how they used opamps with feedback from the dc side to adjust the timing of the firing pulses on primary side kinda thru me for a loop
Oh. SCR preregulation, Interesting. I have heard about triac driving transformer primary to do same job but this is more clever though complicated.
Learned a lot. Even I don't have this exact PS, your video had empowered me to get into its repair. Thank you!
BTW, have you seen Mitsuru Yamada's "Assembling of homemade 6502 computer PERSEUS-8 enclosure"?
Nice and professional video.
Can I dowlod the schematic of PS ?
Thanks
Good video, as usual, though a glitch in the matrix : )
what glitch?....................what glitch?..................what gli
Shame you cannot use a MC1350.
why did you add the wire from the negative post to the ground post ?
old habit. HP supplies usually shipped with a shorting wire (stamped metal). The ground references the negative side so there are no surprises with it floating too high and getting you in trouble connecting to a ground referenced system.
anyway, i think its a good idea to make clones of it
You repeated yourself!!