|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
63.246.183.22
I've just spent several days of spare time tracking down one of the oddest problems I've ever seen. It started when I decided to bench test the individual components from a Leslie speaker - audio amp, power supply and motor control - for the purpose of transplanting them into a different cabinet. When I hooked up the control unit to the motors, the fast speed motor would growl and crawl for a second or two, then stop. It would do this every time power was applied. The slow motor was fine. Both motors worked OK after the initial weirdness; grounding either control line would activate and run the respective motor perfectly.In this controller, each motor is driven by a reed relay that activates a triac, a very straight forward circuit. While troubleshooting, I discovered that the bad driver would exhibit the problem even if I disconnected the coil of its relay. That particular relay had been replaced with a Radioshack version by a previous owner though, so I decided something was probably wrong with the contacts. I replaced it, but no go, same problem. Next, I replaced the triac. Again, nothing changed, same problem. Now grasping at straws, I thought it might be the motor itself, some sort of inductive kickback forcing the triac to conduct. So, I disassembled the Molex connector for the motors and swapped them. Now the slow motor had the problem. I swapped the motors back, then disconnected B+ to the controller board. That kills all the control circuitry, leaving only the AC going to the triacs. Still did it.
After several more hours of illogical troubleshooting, I finally found it. Almost unbelievable, it turned out to be the proximity of the power transformer to the relay/triac circuitry. The bad driver is right next to the transformer; the good channel several inches away. I finally proved it by inserting a piece of sheet metal (steel) between the transformer and the control board. Problem gone! All that time, I was fighting a factory anomaly. Apparently, they all do it! Good grief...
--------------------------
Buy Chinese. Bury freedom.
Edits: 08/20/16Follow Ups:
Shielding...
Wow, that place has some very interesting materials! I do have Ultraperm sheets (mu-metal), but the stuff is expensive. I reserve it for phono preamps and such. Thanks for posting that link, it will be a great reference for future use.
About the controller, I've decided not to pursue it. They all do this, so it's just an odd quirk at this point. I added a snubber to the master control relay (contacts were arcing a little), and I just finished a minor repair on the power amp. Everything is almost ready to be mounted in the cabinet.
--------------------------
Buy Chinese. Bury freedom.
Works very well... Very powerful material... Check out the whole series of 3M products at the bottom of the page...Edit... Cheaper prices...
Edits: 08/21/16
Transformer that close to the relay would interfere (induce) with the function of the relay due to the coils inside the relay. So a simple shield was the answer huh? Nice find!
Actually, I've decided not to fix this issue. I don't have a metal brake to make a permanent shield, but more important, the false trigger doesn't actually harm anything. My only concern at the beginning was that a component had failed. I spent way too much time on this just to find out that isn't the case. Darn engineers...
--------------------------
Buy Chinese. Bury freedom.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: