Repair of RAPID PSU 30 Amp 3 to 20v Bench Power Supply to component level, Model 85-1711

He we have a common bench high current power supply commonly used with High power RF amplifiers & land mobile radio systems, Ham Radio transceivers & electronics applications. these use 5x 2N3055 series pass transistors with 0.1 ohm emitter balancing cement resistors to provide a max output current of 30Amps, the supply is rated to 25 Amps continuous. Using electronic fault finding principles We confirm the fault, look at the safety concerns when working on the power supply, theory of operation, & discuss the configuration & architecture of the PSU bearing in mind we have no circuit diagram or service manual we have to reverse engineer the system to understand its theory of operation.Following this we discover a defective power transistor & begin pinpoint measurements of the collector, base & emmitter junctions to confirm their status of each of the 5 transistors. we isolate the suspected component & verify the defective transistor ensuring there isn't a secondary fault. Upon reassembly we discover another issue with the ammeter on the front panel having its bezel moving unrestricted due to the glue holding it in place breaking down, we re glue both the ammeter & voltmeter bezel & re assemble. Last step is a confirmatory test to ensure all is well before considering the repair sucessful.

[@mushtaqobaray7529]

Excellent explanation, the most important part of feed back of voltage and current was too short, it is here, most of us get stuck up by the complex op Amp circuitry.

[@alandrury9955]

Nice repair. Where do you find all this faulty stuff?

[@lesjones5684]

Do I need 30 amps for my cobra 138 xlr

[@lesjones5684]

Thanks bro 😎 😅😅😅

[@lesjones5684]

I have 3 amps 😢😢😢😢lol 😅

[@rfmanrfman4536]

If your radio transmits below 10wayys rf output which most CB radios only transmit about 4 watts you will find the radio will only take about 3 amps so no you don't need a 30 amp psu, however if you purchased a an external rf power amplifier to boost your TX power to say 100watta or above then those take about 20 amps to power so in that case you would need 30 amps, so as you can see it varies, if you just have a radio of 10 watts or less a 5 amp power supply will be fine.

[@sbelectronicaindustrial6652]

👍👍 Hi..!! Very, Very Good...!!