That's a strange, "upside down" feedback comparator. The Zener reference & comparator transistor base are negative of the output voltage, so the voltage divider with the setting pot it causing the emitter to go more negative (relative to the reference) as the output voltage increases! It looks backwards at first glance, until you work through the whole thing. Neat & clever design.
Jerry, that is an H740 power supply, isn't it? From a PDP-8/F or PDP-8/M computer? Also, what "modern" foam do you recommend for the missing foam in this PSU? Thank you for sharing this repair with your detailed troubleshooting techniques! Definite thumbs up!
I hate power supplies! When I was a young lad in the Navy (about 100 years ago), we had a power supply from something (don't remember what) but it used 3 feedback loops to regulate the power including one that actually controlled the input AC before the transformer. It had a great manual with voltage readings on every component in the schematic. The problem was that 100% of those reading were wrong because of the feedback loops and we did not know enough to figure out how to isolate anything. We took out every solid state device and checked them on a curve tracer but could not find anything bad. It was probably a bad resistor!!! I think the power supply was still broke when I transferred from the site.
They probably designed them that way to keep you busy. Same as the army painting rocks white. Remember the main rule in the forces, 'If in doubt then designate'.
Are you going to continue the series on designing and building a switching power supply from the 1980's era. I remember you were having difficulty obtaining cores for the inductors as they were always broken when they arrived. It was very interesting.
@@JerryWalker001 Ah good to hear, I just came here to say the same thing. I was very interested in that series. I would actually love to see a video on designing a power supply like this one, and those found in other pdp-8 and pdp-11 era machines with a big mains step-down transformer and a switching regulator.
Hi Jerry! I'm interested in using a few second clip of one of your repair videos as part of a >30 minute video I'm working on. I can't seem to find a contact email or social media on your page. What's the best way to get in touch with you? (Keep in mind youtube usually deletes comments with emails or URLs in them, even if posted by the person who owns the channel)
@@ShankMods As you say TH-cam generally removes comments with web addresses. I mention the site in various videos but if you google 'Vintage computer repair' it should be listed on the first page (jm...........uk)
Great content as always! Your videos have so much potential for reaching an even larger audience. Keep up the amazing work, and if you ever want to chat about ways to expand, feel free to reach out
Very nice, I could watch nice systematic repairs like this all day long...cheers.
That's a strange, "upside down" feedback comparator.
The Zener reference & comparator transistor base are negative of the output voltage, so the voltage divider with the setting pot it causing the emitter to go more negative (relative to the reference) as the output voltage increases!
It looks backwards at first glance, until you work through the whole thing. Neat & clever design.
Yes it does not matter the polarity of the error signal as long as the 'control' elements operate accordingly.
Jerry, that is an H740 power supply, isn't it? From a PDP-8/F or PDP-8/M computer? Also, what "modern" foam do you recommend for the missing foam in this PSU?
Thank you for sharing this repair with your detailed troubleshooting techniques! Definite thumbs up!
I hate power supplies! When I was a young lad in the Navy (about 100 years ago), we had a power supply from something (don't remember what) but it used 3 feedback loops to regulate the power including one that actually controlled the input AC before the transformer. It had a great manual with voltage readings on every component in the schematic. The problem was that 100% of those reading were wrong because of the feedback loops and we did not know enough to figure out how to isolate anything. We took out every solid state device and checked them on a curve tracer but could not find anything bad. It was probably a bad resistor!!! I think the power supply was still broke when I transferred from the site.
They probably designed them that way to keep you busy.
Same as the army painting rocks white.
Remember the main rule in the forces, 'If in doubt then designate'.
Are you going to continue the series on designing and building a switching power supply from the 1980's era. I remember you were having difficulty obtaining cores for the inductors as they were always broken when they arrived. It was very interesting.
I will most likely continue the series at some point but I still need to find some cores.
@@JerryWalker001 Ah good to hear, I just came here to say the same thing. I was very interested in that series. I would actually love to see a video on designing a power supply like this one, and those found in other pdp-8 and pdp-11 era machines with a big mains step-down transformer and a switching regulator.
Hi Jerry! I'm interested in using a few second clip of one of your repair videos as part of a >30 minute video I'm working on. I can't seem to find a contact email or social media on your page. What's the best way to get in touch with you? (Keep in mind youtube usually deletes comments with emails or URLs in them, even if posted by the person who owns the channel)
You can contact me through my website
@@JerryWalker001Thanks for the reply. I'm struggling to find the website. Where is it listed?
@@ShankMods As you say TH-cam generally removes comments with web addresses.
I mention the site in various videos but if you google 'Vintage computer repair' it should be listed on the first page (jm...........uk)
Great content as always! Your videos have so much potential for reaching an even larger audience. Keep up the amazing work, and if you ever want to chat about ways to expand, feel free to reach out