- 2025
- Sep
- 3
A Workman Electronic Products N71-067 Power Supply - The Repair
After poking around in the power supply for a little while, I believed that the LM723 was probably bad. However, something didn’t set right. A few more checks and there it was - while the output transistor was fine, the driver transistor area had a substantially lower resistance than the surrounding parts would suggest. I pulled it out, and for all intents and purposes it’s shorted C-E.
That’s an easy fix, it’s a S8050 transistor. I had to place an order for some other things, so I ordered a batch of transistors.
It was easy enough to install
However, since the LM723 probably was quite stressed from this failure, I decided to replace it as well. I just cut it out and pulled the pins from the solder pads, then removed the solder with wick. That 1970s phenolic board smell! It’s going to get socketed just in case. (Finding these in DIP is getting kind of difficult!)
Since the big filter was quite old, I replaced it as well. Here’s a shot of the completed and re-installed board:
And, it works!
So what all was replaced?
The S8050 driver transistor for the series pass regulator.
The LM723 Regulator IC
The main filter capacitor.
I did dial the output back a little to 12.8VDC, just because I want this on my bench for other things.
A relatively easy repair, but there’s not much in this thing to go wrong. Next up is starting the actual rebuild on the Heathkit AG-7, stay tuned!
Previous part of this series: https://wereboar.com … /[url]