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Old 12-29-2010, 07:26 PM   #11
Old N00b
Join Date: Dec 2010
City & State: Claremont, CA
My Country: USA - West Side!
Line Voltage: 120VAC 60Hz
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Posts: 160
Default Re: Hanns-G HG281D 28" TFT - Multiple Problems

Hope everyone had a merry christmas!

In the absence of a proper camera with which to take pictures of the board, I proceeded to troubleshoot it on my own. Here's what I've come up with so far:

I checked all components on the board for shorts and open circuits, including all diodes, transistors, schotkeys, the rectifier IC, SMDs and caps. I found none. (I did not properly check the transformers though.)

I changed out the fuse, reassembled the unit and plugged in the power cord. Immediately the slo-blo fuse popped (loudly) again, the lamp connected to the same outlet dimming dramatically in the instant before the fuse blew.

I took the board out again and rechecked for any visible damage. Only the fuse seems to have blown.

So I read up on LCD monitor repair, learned a bit more and then checked the transformers out with my multimeter (digital, unfortunately).

T2 & T3 checked out ok in circuit, but T1 seems to be shorted between all pins on the secondary ("B") except pin 4. Resistance measurements between pin 4 and all other pins on B seem to be consistent at .6 ohms. Measurements between all other pins in B come up as close to 0 ohms as the meter will get (.3).

Resistence between 1 & 2 on the primary ("A") measures .4 ohms.

I have been attemting to remove the transformer from the circuit but have found my soldering iron to be inadequate for the task. Time for a new iron I guess. It is an Unger 35 watt. It's about 25 years old. It could just need a new element or I might need a hotter iron. Any suggestions in this regard would be very much appreciated!

Is it necessary to remove the transformer from the circuit to check it properly with a meter? Unfortunately I don't have a flyback tester - and I can't even find a single repair shop within 100 miles that uses them anymore. (What is wrong with all these "repair shops" nowa-days?? They don't even do component level work anymore, they just replace entire modules!)

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File Type: jpg PSU-Back-X1_Notated.jpg (763.6 KB, 152 views)

Last edited by stevekasian; 12-29-2010 at 07:29 PM..
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