Fixing the switching power supply

This particular power supply is used in Broadcast Electronics AM1A, AM2.5E, AM5E, AM6A, AM10A, FM1C, FM10T, FM20T, FM30T and FM35T transmitters. It is a Computer Products NFN 40-7610, 40 Watt, +5 VDC, +/- 15 VDC BE part number 540-0006.

BE AM1A ECU power supply, C-15 marked with pen for replacement

Generally, one component fails over time on this unit, C-15 which is a 680 uF 35 V electrolytic capacitor. When that capacitor dries out, the power supply will fail to start, do odd things like start and fail after a second or two, or cycle on and off. This will happen after the transmitter has been off for a few minutes. Replacing C-15 with a 1000 uF 50 V capacitor will fix the problem. There is enough room for the larger capacitor if the leads are left a little bit long.

BE AM1A repaired ECU power supply re-installed

We have several of these repaired units on various shelves at various transmitter sites.

As always, when replacing electrolytic capacitors, pay attention to the polarity otherwise this will happen:

Blown Electrolytic Capacitor installed backward

I suppose somebody was in a hurry to get home that day. After I installed this repaired unit, it ran for about 15 seconds and then there was a pop. I opened the door on the ECU and white smoke was wafting out from under the power supply cover. Since the Pope is still The Pope, I knew it was the electrolytic capacitor.

Back in business

Our beloved BE AM1A is back in service. This transmitter is 22 years old and we can keep it going for as long as parts are available.

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5 thoughts on “Fixing the switching power supply”

  1. The best feeling in the world…gobs of Forward power, zero reflected!

    I did that on a 22 uf/350 V electrolytic in a receiver power supply, once. 5Y3 lit up like a rocket, supply off, fans on high for the fried electrolyte smell…

    I wonder how many perfectly good broadcast devices get trashed because of repairable things like electrolytics.

  2. I’ve seen a large electrolytic vaporize into a hazy cloud of fishy smell and little bits of aluminum floating in the air.
    (OK that was on purpose to see what would happen… and I was 15.)
    Stole a power supply out of an XDS receiver to get a BE 1C1 back up.

  3. When replacing these components I do The same thing that Paul did, use a higher voltage rated capacitor. It’s usually larger, so it runs cooler, and does not dry out as quickly as the original. For even more longevity, I use 105 degree rated capacitors instead of the cheaper 85 degree caps.

  4. Whenever I replace an electrolytic , I have a habit of marking the PCB with a sharpie where the negative marking is with a small dot. It leaves room for error on reversing to a minimum. Especially if in the middle of it, I get distracted by a radio call or what-not.

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