Testing C5707 Transistors on Benq Inverter Board

Hello everyone,


I have a faulty HP 1940 with a Benq 48.LIG02.A01 inverter board. It has the fault where it the screen goes black after a few seconds, after putting a flash light to it I could see that the image was still there. i Opened it up and inspected the inverter board I could not see any faulty caps and the soldering looks good to me (I'm a novice) so after reading through the posts here I decided to pull the four C5707 transistors off the board and test them with my DMM, as I have read here that these transistors are a common fault with this board. Because I have little experience testing transistors I was hoping for some conformation from the experts (you)


I pulled 4 transistors off the board and kept them separated in pairs as I'm told the fail in pairs.


The first pair gave me the following results (all tested with the diode function on my DMM)


Transistor 1 (first pair)


B-E .575 v
B-C .575v
C-E Open
E-C Open


Transistor 2 (first pair)
Same as above


Transistor 3 (second pair)
B-E 0.00v (it did not read 0L )
B-C .349v
C-E .349v
E-C .360v


Transistor 4 (second pair)
B-E 0.00v (it did not read 0L )
B-C .444v
C-E .478v
E-C OPEN


it seems to me that the second pair is faulty I was wondering if anyone can confirm this? I have found a place on ebay where I can order some new C5707s. Also As a precaution I have touched up the soldering on all the transformers in case this was the cause of the fault. Anything else I should check?


Thanks heaps for all the great tips I found here I would never have tried this without the advice I have found on this site.


Mike