It's a job I've been avoiding for oh, say, 10 years...but my Heathkit AP-1800 was finally just about impossible to live with. Working on the preamp didn't scare me as much as disconnecting it. It's the central nervous system of a vast number of components. I think there are 12 or so pairs of inputs and outputs connected.
The preamp constantly cut out one or both channels of every source. The mode switch, input switch, output switch and volume control all needed cleaning. I figured if I was going in, I might as well be as thorough as possible. I built the preamp about thirty years ago and once I got the unit apart, that interval became sadly apparent. I can't SEE anymore! I used to be able to read the part number off a crystal diode in half-darkness. No more. My kitchen was lit up like an operating room and I was wearing magnifying glasses and a head-mounted flashlight. It was barely enough.
The input switch and mode switch are both rotary-to-linear operated and have 56 pins soldered into the control circuit boards. Five feet of solder wick later, I had them both out. I opened them up and cleaned the wipers and contacts with deOxIt and a pencil eraser. I used deOxIt gold afterwards, reassembled and then moved to the volume control. I took that apart and used the same procedure to clean. Shot the rest of the controls without disassembling and then put the unit back together.
After hooking all the components back up, I tried the turntable. No left channel! BUT, the phono input worked if I had the cd player on. WTH? I suspected a solder bridge. Never really had to deal with one, but like I said, I can't see anymore. I finally found that I did have a bridge, scraped it out and reassembled once again. I swear this thing sounds like new again. I put together an AA-1800 at the same time I built the preamp. I love the old equipment and I look forward to another thirty years (by which time I'll be pushing 90) of good listening.
The preamp constantly cut out one or both channels of every source. The mode switch, input switch, output switch and volume control all needed cleaning. I figured if I was going in, I might as well be as thorough as possible. I built the preamp about thirty years ago and once I got the unit apart, that interval became sadly apparent. I can't SEE anymore! I used to be able to read the part number off a crystal diode in half-darkness. No more. My kitchen was lit up like an operating room and I was wearing magnifying glasses and a head-mounted flashlight. It was barely enough.
The input switch and mode switch are both rotary-to-linear operated and have 56 pins soldered into the control circuit boards. Five feet of solder wick later, I had them both out. I opened them up and cleaned the wipers and contacts with deOxIt and a pencil eraser. I used deOxIt gold afterwards, reassembled and then moved to the volume control. I took that apart and used the same procedure to clean. Shot the rest of the controls without disassembling and then put the unit back together.
After hooking all the components back up, I tried the turntable. No left channel! BUT, the phono input worked if I had the cd player on. WTH? I suspected a solder bridge. Never really had to deal with one, but like I said, I can't see anymore. I finally found that I did have a bridge, scraped it out and reassembled once again. I swear this thing sounds like new again. I put together an AA-1800 at the same time I built the preamp. I love the old equipment and I look forward to another thirty years (by which time I'll be pushing 90) of good listening.
The problem remains, but I fixed it again. Well, sort of...
