Thanks, Spud.
Things are at a standstill now until the LEDs show up. So, with nothing else to do, I broke open the original 7v regulator to see if I could reverse engineer it. I'm not real happy with the VR I built, too much output fluctuation if the input fluctuates. I've looked into it and will have to do some mods.
Anyway, opened the original VR and spent the the better part of an hour breaking off the resin potting compound. What I found was an IC, possibly an LM317 VR,(can't tell as the markings are gone), 3 diodes, a power transistor, a ceramic cap, and maybe five 1/4W resistors. I also found the CB cracked. :?
Looking under a 5X magnifier, I counted three solder joint breaks. I repaired these and hooked up to my 12V power supply. Surprise, surprise, I had 11.9V at the IC.
Unfortunately, nothing at the output. :? I started checking the CB with my DVM and found 6.9V at the output of the IC but still nothing at the output terminal. So, working backwards from the terminal towards the IC, along the board with a DVM, I hit a spot where I was getting 6.9V. Move back towards the terminal, nothing. It took a 12X magnifier to spot the break. Half a second with the solder iron and, voila, I have a working stock VR.
How well does it work? If I drop the input at the power supply from 12V to 9V, the output only drops 0.1V. If I increase the input to 15V, the output doesn't increase.
As pleased as I am that the stock VR is now working, I'm still going to reverse engineer it with all new components. Why take a chance with 33 year old ICs.
Look how tiny that thing is.
