- 2025
- Oct
- 3
The Heathkit AG-7 Audio Generator part 6: Removing everthing.
In the last post, I checked a few parts and found that pretty much every resistor (that I could measure in circuit) was out of tolerance, in a bad way. Seeing as how the device stopped oscillating, and started smoking, I decided that replacing everything was the best course of action.
I’m trying to save the old parts for later testing purposes, so unsoldering with intact leads is a must. That does tend to make it’s own problems, something we’ll discuss later on.
Here’s what I recovered (save the 10k removed in a previous step):
The chassis is now empty.
For testing, I just grabbed my scope-meter and a capacitor checker. I’m not really worried about ESR or leakage here, they’re just old and probably have issues with both.
So on to the good stuff. How bad do the parts test? Well, that’s the fun part. Most of them are ok-ish, even the ones that read substantially higher in circuit. The 100k in the previous post? It’s back to well within in tolerance range.
What happened here? Carbon Composite resistors change value over time because the carbon grains disassociate with one another, and they collect moisture. I hit these with some high heat during the desoldering process, which probably drove out the moisture and brought them back near tolerance. I suspect if I left these alone for a year or so, they’d be back to what they were. Perhaps I’ll segregate them and do a follow-up next year.
Of particular note was that 270Ω part that read 2.6kΩ. While this looks brown to me under normal lighting, the camera shows it has more of a red hue. This guy must have been pretty warm over the years and the color simply faded. It’s actually marked 2.7k.
Next up is actually placing new parts. Check back soon!
Next part of this series: https://wereboar.com … ion-thats-not-right/
Previous part of this series: https://wereboar.com … nna-need-everything/