I have a Heathkit IP-2715 power supply that needs work. It worked good yesterday, now today just buzzing from transformer and nothing else. Does anyone work on this kind of equipment or know someone who does? I need help. Thanks Mike

Hi Mike,

I assume you checked both the 7 and the 20 amp fuses.
The circuit is actually quite simple and reminds me of an Astron 20 amp supply but with older components. The chip regulator at the center is a Heath 442-626 which crosses to a 78MGT4C. The chip is the heart of the unit and controls two smaller transistors in Darlington configuration which in turn control the bases of the four large pass transistors. Unlike the Astron circuits, it has no over-voltage crowbar SCR. That makes troubleshooting a bit easier although it might make a ham radio user nervous about connecting an expensive transceiver to it.

The 78MGT4C is an obsolete part but I suspect an LM317 could work quite well as a modification.

You need to do some voltage checks to see what part failed.

I assume you have the schematic and / or manual.

-- Rich

It is beyond what I can do. Every thing is soldered together and I can't solder very good. I am learning but, this needs someone that knows what they are doing. You sound like you know what you are doing want to fix it? Another person told me to check white wires for 30 volts. I can't even find them. I can replace tubes and maybe a cap but that is far as I can go. Thanks for the info and let me know if you want to fix it. Mike Andrijeski

If you want to send it to me I will take a look at it.

Good call.

http://lists.tempe.gov/admin/WA.EXE?A2= ... th&P=14285

If you would give me your address I'll send it to you. Here is my email address: Mike100860@yahoo.com I will pay you what you think it is worth and parts. Mike

I am repairing a Heathkit IP-2715 power supply for a friend. The regulator chip, P/N 442-626 is blown. I want to substitute a 714 op amp by (I think) grounding the V+ input and use the V- input to get an inverting function from the chip. Does anyone have experience doing this, or do you have another sugggestion? I replaced both Q1 and Q2 (2N3055) which were blown. All four output transistors are good, and by injecting current into their bases I can get an output. All other components (caps, diodes, etc. check OK).
Thank you, NIKT

The old chip was an oddball voltage regulator chip, not easy to find nowdays. A 741 is not a direct drop-in, you'd have to do a lot of engineering to set up a reference voltage, and anti-oscillation dampers, and it would probably still burn up in the end. Power supplies are a lot harder that one thinks.

I would just junk the power supply. It was never a very good design-- no current limiting for one thing.

Hi
I have a 78mgt2c, I don't know what the difference is, does anyone know or have a data sheet? Let me know if you are interested. It's never been soldered in a board, so I will have to assume it's good. Without any info, I can't test it.

To old fart and Ancient_Hacker:

Thanks for your thoughts, but I am, if anything, persistent. If it takes a redesign, so be it. I will look up the chip you mentioned to see if it will do, either as is, or with circuit modification. I will get back to you.

I hate to give up on the supply as it has a pretty decent transformer with plenty of copper and iron in its construction. My friend plans to use it as a utility supply for small scale experiments and charging small batteries, so he said to have at it. I have experience in working with solid-state switching circuits, so if all else fails, I'll try to make this a switch-mode power supply.

Best regards,

NIKT