The main supply is only used for the PA, so a bit of AC there won't cause hum in the audio. Check the regulated 9.6 and 12.v supplies on the PC board, these tend to dry out the 100uf caps causing hum. A simple check with a scope will tell all. Motorola's spec on AC is 60millivolts, max. on any supply. if your main supply is sagging below 13.0 volts, check the 2 chassis mounted diodes. it is normal for this part of the supply to start out at about 15.5 volts and drop to as low as 13 ( normal). lance N2HBA ----- Original Message ----- From: kk2ed To: Repeater-Builder@yahoogroups.com Sent: Thursday, January 17, 2008 10:59 PM Subject: [Repeater-Builder] Micor power supply issue
Good Evening, I have a Micor 75 station power supply that is acting up. When the repeater is idle, the voltage output appears clean. But as the load is increased (ie: power output increased), the voltage sags and I get an annoying hum on the tx (indicative of AC ripple on the dc side?). It started out as a barely noticeable hum; the past few days it has gotten to the point where I just shut down the repeater's tx. I haven't had a chance to get to the site to swap it out with a spare. But I'm curious as to what kind of repair I'm in for, and others' experience with Micor supplies. What tends to be the failure and/or cause of the above condition? Pass transistor failure? Filter caps? Ferro-resonant circuit (cap)? Thanks for any input Eric KE2D
