I have spent the greater part of the last two days looking over this excellent forum regarding a debug/repair/enhancement strategy for the power supply in the HP 1955 LCD monitor (which goes under the Benq project code of 48.L1A02.A00).
I have concluded that the 2SC5707 transistors require replacement (two are shorted) as well as the 5A pico fuse (replace with a 3A). I have resoldered all thru-hole connections on the PWB (especially the transformers) and found several cracked solder joints in the process. I have removed the Royer oscillator tuning caps and verified out-of-circuit that they are of the proper value and tolerance. I am now awaiting my replacement parts (including a complete new set of electrolytic capacitors) in order to button this up.
Two issues remain, however ...
1) Has anyone been able to put their hands on a bona fide schematic for this particular power supply board? I have seen several requests in the forum over the years but no postings.
2) DavMax posted a series of circuit modifications and improvements to a Benq Q7T3 monitor that addresses overcurrent protection under a variety of scenarios. Some of his threads were intertwined with the HP1955 threads, but I think some adaptation is required to incorporate them into the design of the Benq 48.L1A02.A00 power supply (ergo, I am looking for the scheamtic). Can anyone shine some light on this? My supposition is that all the Benq inverter supplies follow the same basic design, but the devil is in the details.
In an attempt to make order out of chaos, I have also begun to compile a comprehensive parts list for this board in Excel, including reference designator, device, part number, function, etc. (amazingly, there are over 220 components on the front and back sides of this board). It should be sufficiently mature for public consumption in about a week or so; sooner, if I can get answers to the two questions above.
Thanks in advance ...
--tbg
I have concluded that the 2SC5707 transistors require replacement (two are shorted) as well as the 5A pico fuse (replace with a 3A). I have resoldered all thru-hole connections on the PWB (especially the transformers) and found several cracked solder joints in the process. I have removed the Royer oscillator tuning caps and verified out-of-circuit that they are of the proper value and tolerance. I am now awaiting my replacement parts (including a complete new set of electrolytic capacitors) in order to button this up.
Two issues remain, however ...
1) Has anyone been able to put their hands on a bona fide schematic for this particular power supply board? I have seen several requests in the forum over the years but no postings.
2) DavMax posted a series of circuit modifications and improvements to a Benq Q7T3 monitor that addresses overcurrent protection under a variety of scenarios. Some of his threads were intertwined with the HP1955 threads, but I think some adaptation is required to incorporate them into the design of the Benq 48.L1A02.A00 power supply (ergo, I am looking for the scheamtic). Can anyone shine some light on this? My supposition is that all the Benq inverter supplies follow the same basic design, but the devil is in the details.
In an attempt to make order out of chaos, I have also begun to compile a comprehensive parts list for this board in Excel, including reference designator, device, part number, function, etc. (amazingly, there are over 220 components on the front and back sides of this board). It should be sufficiently mature for public consumption in about a week or so; sooner, if I can get answers to the two questions above.
Thanks in advance ...
--tbg
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