Is each individual device that's running off that power supply independently fused in its A+ lead? If so, and none of those fuses are blowing, that points back to the crowbar circuit in the power supply. If not, fusing each A+ lead may help to isolate which device is drawing too much current after extended key-down.
Adding an EMI/RFI filter to the PS line in might help (if you need one, I have a few laying around, scavenged from various devices), and I saw a message in another ham group over the weekend where someone had much better RFI suppression results using powdered iron toroids rather than ferrites... #6 mix (red) 2-1/2". . George, KA3HSW / WQGJ413 ________________________________ From: n9wys <[EMAIL PROTECTED]> To: Repeater-Builder@yahoogroups.com Sent: Monday, December 8, 2008 9:20:23 AM Subject: [Repeater-Builder] Astron P/S question For the learned group here… I know there has been some discussion on one the list regarding Astron Power supplies. Unfortunately, searching hasn’t revealed what I am looking for, so I pose my query here and apologize in advance if this was a subject that was discussed at length in the past… I will describe my problem in detail, so forgive me for being so verbose right off the bat; but I figure if I provide a lot of info now, it will avoid a lot of question and answer exchanges later in order to get an understanding of my problem. I have a UHF ham repeater system (TKR-820 as transmitter, MICOR SpectraTAC receiver and comparator, Astron RM-70 Power Supply, and Crescend 150W P/A) that is experiencing issues with the power supply. Seems that when the repeater is on the air for any time (for example, over three minutes key-down) the power supply blows a fuse. The first time this happened, I changed out the P/S with a MICOR supply I had from a 100W continuous duty station. It also blew THAT fuse… The Astron supply that blew the fuse had two bad diodes in the rectifier, so that was repaired. There was nothing found wrong with the Motorola supply, other than the main fuse had blown. I took the PA back to Crescend, but they found nothing wrong with the P/A. The station was put back on the air with the repaired Astron supply. Was on the air for about two weeks, and failed again while I was talking to another ham. Went back to the tower and found the fuse blown again in the supply. I took the PA offline and brought it back to Crescend, told them of the issue with the P/S, and that I needed them to check the PA for problems. Their service tech called me and said he’d had the PA running on his workbench as we spoke, and had it transmitting for about 45 minutes with no problems – all operating within spec (~32A nominal - 38A max draw @ 165W output). After we talked some more, he said he’d leave it run all night. If it was OK, he’d ship it back. I got the PA back the following Tuesday. I put the station back on the air… In the meantime, I spoke with an engineer from Crescend who told me that they had some experience with RF getting into Astron supplies… so when I took the PA back to the tower, I put ferrites on the A+ and ground leads to the P/S from the PA. (There are about 10 wires altogether in the power cable going to the PA – two bundles of three A+, and four Grounds.) I put three ferrites altogether on the DC lines, and made three turns through the ferrites with each bundle. These were installed as close as physically possible to the power supply. I also put one turn on a ferrite for the entire bundle at the PA end. (Couldn’t do more than that – was running out of cable length for hook-up.) I replaced the fuse again, and got the station back on the air. Worked for about 45 minutes (or long enough for me to be far enough away from the tower where I couldn’t make a return trip that day) and promptly blew the fuse again. (Or so I suspect.) I haven’t had a chance to go back to examine the cause of the failure this time – yet. Now – here’s the WEIRD part… when I was at the tower with another tech and replaced the fuse the time before the last failure, we tried to use his DMM to check the P/S fuse for continuity. His meter acted as if the battery was dead – but later investigation revealed that the meter was getting hit with RF from another transmitter at the site. So I’m thinking that the RF problem may or may not be directly related to MY transmitter. (There is VHF 100W MICOR transmitter directly next to my equipment rack that is on 161.325, and transmits 24/7/365.) OK – here are the questions: 1) Has anyone experienced an issue with RF getting into Astron power supplies, and how did you remedy the issue? 2) Since the P/S fails only when my transmitter is on the air, could I be getting a mix of RF (the VHF and my UHF) that is causing this? To answer a question that may be posed, I do not have a SpecAn available to me to check for spurs, but I am contacting the county radio tech (it’s a county-owned tower) to see if he can assist me with this. Any ideas, other than purchasing a “hardened” power supply, that could remedy my situation? Thanks, Mark – N9WYS
