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Posts Tagged ‘Electronics’

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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UPS Repair – Part 3

March 29th, 2012 No comments

New relays have been fitted, the unit reassembled, and powered back up. So far everything looks good, but I won’t know for sure if the problem has really been fixed until I get some under or over voltages, but I’m fairly confident of the repair.

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UPS Repair – Part 2

March 24th, 2012 No comments

I’ve stripped the UPS down and removed the main circuit board. After a quick examination I identified four likely relays and then extracted them for testing.

Relay R406 had a high resistance across a couple of contacts, so this looks to be the AVR relay. One of the other relays (I forget which) also sounded a bit tired when I was testing it.

What I plan to do next is replace all four, since I’ve already gone to the effort of removing them. The original relays are Song Chuan 793-P-1C-3. I’m going to replace them with Omron G2R-1-E 24DC from CPC. I’ll get them ordered up within the next few days, and hopefully have it back together before the end of next week.

 

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UPS Repair – Part 1

March 23rd, 2012 No comments

I’ve a small project that should keep me occupied for a short while. I recently got my hands on an APC Smart-UPS X 1500VA (SMX1500RMI2U) which was heading to the skip. It had been replaced by an identical unit after it had developed a fault. Needless to say it happened not long after the warranty had expired, and it was not considered worth repairing.

The issue with this UPS is an “AVR Relay Weld” fault. Hopefully this should be an easy fix, assuming I can get a replacement relay, once I identify the exact offending component.

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