So my HP 6114A recently gave up. Had it just running on the desk powering a switching regulator I was experimenting with and it fizzled. (Let out a ton of magic smoke while it was at it...) I have had this brick for about 6 years. I saved up mowing lawns for quite some time before purchasing it at a hamfest. At the moment I feel like I am back in the stone ages with a computer ATX supply and some home made linear supplies.
So onto the repair. When I turn it on I can hear the transformer humming. the meter shows above max current (2.4A), and the overcurrent light is on.
The magic smoke all came from a 1
resistor on the board. It is connected between ground and the emitter of one of the four transistors(? more on this in a moment) on the rear heatsink. Pulling the TO-3 package off the heatsink it simply states "V0 7423452 RCA" I instantly get a feeling of dread as this looks like an in-house part number. Google was no help at all. Testing it, the "can" and the "E" pin are shorted and the other pin has a ~0.4v drop to the case and the "E" pin. I am assuming that "E" on the pcb stands for "emitter" as the same pin is labeled likewise on all three other TO-3 cans.
It is here that I hit a standstill as I cannot find a replacement for the part. Are there any suggestions as to a possible replacement? Could it just be a rebranded 2N3055 (or similar) as RCA is known for doing a custom number for a single product.
Schematic of similar model: (Snitched from here:
https://www.eevblog.com/forum/reviews/would-you-pay-$100-for-a-hp6115a-psu/msg284891/#msg284891 )
Wondered if the SCR is kicking in and shorting the output. Pulled the drive resistor for it (R27, 47 ohm) and nothing changed. Put it back in.
Replaced the totally smoked 1ohm resistor (R10, 1ohm 5%) with 10 10 ohm resistors in parallel (all I had around.) and now when I turn it on it doesn't ping to full power on the meter. I can adjust the current limiting knob and make the meter movement change from between 0 and 0.2A.
Thanks,
Nathaniel.
Oh, and is $140 a good price for a used 0-300v 0-3A DC power supply? The ripple is quite bad rated (700mv at max voltage) but it has constant current and voltage. (Yes you read that right. 300V DC.)