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Kramer VP-725DSA Repair – Part 1

January 2nd, 2013 No comments

I’ve acquired another bit of hardware that was heading towards the skip – a Kramer VP-725DSA Presentation Switcher/Scaler. Its problem is that it no longer responds to any of the buttons on the front control panel, and is permanently stuck on DVI 1. When controlling it via its network control application, it does respond to the virtual button presses, but then almost immediately jumps back to its previous state, and intermittently does a factory reset.

First up I whipped out the front control panel PCB and checked out the DVI 1 button. The button checks out as I had suspected, and I turned my attention to the switch mode power supply (SMPS).

The four voltage rails (+5, -5, +15 and -15) all tested fine, but on further inspection the resistor R3 looked rather crispy. Even with no load attached to the output of the SMPS, the resistor gets pretty hot. I’ve tested the resistor out of the circuit and it reads 75K, which is what I guess it should be. The colour bands are rather cooked – currently purple, black, brown, gold, but they may have originally been violet, green, orange, gold.

For now I’m going to focus my attention on the SMPS, as I suspect there’s some issue with its output which is upsetting the rest of the unit – excess ripple, noise, etc. I’ve just got to track down what is pulling excess current through R3. I’ve emailed Kramer to see if there’s a service manual available before I start poking around further. I guess that one of the electrolytic capacitors is out of spec, but there’s no visible problem with any of them.

To be continued…

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