I by Jeff Liebermann AE6KS
On the web page:
http://www.repeater-builder.com/aeroflex/aeroflex-index.html
there is mention of:
"Also, may old IFRs are having power supply problems. If anyone would like to do an article on troubleshooting and repair we'd be happy to put it here."
I don't have a complete article, but it might be of interest to know that I may have found one cause of the power supply problem in an IFR-1500.
I eventually noticed that the board had four large toroids wound with heavy copper wire. On the PS layout below, these torroids are E, F, G, and K. The enamel insulation appeared to be only partly removed. I unsoldered the big wires, scraped off the remaining enamel insulation, tinned the wires, and resoldered them to the PCB with a large hot solder tip. There are also some smaller toroids on the power supply filter board, where I only resoldered the PCB connections, without scraping off any additional insulation. I purchased an IFR-1500 service monitor which was know to have power supply problems. It worked just fine for 6 hours and then just quit. No lights, no fan, no nothing, on both AC and DC power. The seller warned me that this might happen, so it wasn't a big surprise. I took apart the unit, removed the power supply module, removed a huge amount of silicon grease smeared between the power supply case and the rear heat sink, followed the troubleshooting instructions, and got nowhere. Although the power supply is simple enough, there is a large feedback loop that makes troubleshooing difficult. I tested all the electrolytic capacitors with an ESR tester, and found them all to be well within specifications.
I
IFR-1500 Power Supply Components Side
Reassembly was a challenge. I had to decide if I wanted to smear probably an ounce of silicon grease on the back side of the power supply, where it mechanically connects to rear panel heat sink. The mechanical connection is made with two large screws through the heat sink from the rear of the unit. That's not going to make a good thermal connection. However, burying the gaps in huge globs of silicon grease isn't going to help much, so I elected to minimize my use of silicon grease, smearing only a very thin coat around the area near the two large screws. Thermal testing with an IR thermometer and a thermocouple thermometer indicated that this was sufficient.
The IFR-1500 has been working without any problems for the last 4 months, so I guess that was the fix.
2010-11-18 Original
2010-02-05 Rewrite for web page.