Hi all,
I have a Hannspree HF237 that I acquired from a friend. The monitor seems to have the typical symptoms of the "2 seconds to black" detailed in this thread. I will try to provide as much information as possible. Pictures are attached at the end.
Symptoms: The monitor turns on as normal (blacklights and lcd) with an image. Soon after (varying amounts of time, sometimes a few seconds, sometimes 1 minute) the backlights will increase in brightness then go completely out.
Initial Diagnostics: After disassembly and visual inspection, nothing looks inherently wrong (No bulging capacitors, no blown resistors, no cold solder joints). In case there were any bad solder joints, I went over all the connections with an iron and new solder to no effect. Strangely enough, the monitor seemed to work for a longer period of time outside the plastic case (tested for ~1hour), and if I put the case back on then the backlights would go out within a few seconds. This oddity originally made me think it was an overheating issue, though I have not been able to confirm this.
Further Inspection: Taking measurements from the power section of the board shows that fuse, bridge rectifier, and both the 5V and 16V output are good and stable, as well as the 5V output after the optocoupler. This leads me to believe the problem resides in the inverter section of the board.
The fuse on the inverter sections gives a resistance reading of 0.2 Ohm, so it is still good. I also get a good 5V and 16V from the output of the schottky diodes. I will further go on to describe individual components for the inverter section.
Resistors: (measurements taken in circuit, so some measurements may be inaccurate)
Most of the resistor values look close to their nominal values, so this makes me think that they are all OK. There are a few that look to be outside their tolerance ranges, but I contribute this to taking measurements while the components are still in circuit. To be sure, it would be best to remove them, however this would be time consuming, and since there are no scorch marks, it looks to be a waste of time.
Diodes:
The voltage drops across the diodes look correct as well.
Capacitors:
I have not been able to take accurate measurements of the capacitors with my multimeter (likely because they are still in circuit), but these are the following capacitors. The caps look fine visually, and I have not replaced them; however I will likely replace them soon just to be sure.
4, 470uF 25V 105 deg Su,scon (which can sometimes be a suspect brand)
2, 680uF 25V 105 deg Samxon
2, 1000uF 25V 105 deg Lelon
Transformers:
There are 2 SPW-106 inverter transformers with 6 pins for the primary windings and 2 pins for the secondary windings. Each of the primary winding on the transformers give readings ~0.3 Ohm - 0.8 Ohm. The secondary windings give readings of ~450 Ohm. The primary to secondary measurements give and "0.F" or open circuit, which is what is should be. (Correct?). If the transformers are bad, does anyone know where to find replacement transformers? I have looked and the best I can find is a SPW-105 on ebay. The SPW-106 I found does not have the same pinout as the ones on my board.
My final thought was that the PWM controller for the inverter section might be bad, but I have not taken it to the lab at MSU to check with an O-scope. It is an INL837GN, which is relatively easy to find a supplier, however extremely difficult to find a datasheet. The closest thing I could find was this schematic.
I would love to hear your thoughts on what my next step should be. Thank you for your time and effort.
-Pat
I have a Hannspree HF237 that I acquired from a friend. The monitor seems to have the typical symptoms of the "2 seconds to black" detailed in this thread. I will try to provide as much information as possible. Pictures are attached at the end.
Symptoms: The monitor turns on as normal (blacklights and lcd) with an image. Soon after (varying amounts of time, sometimes a few seconds, sometimes 1 minute) the backlights will increase in brightness then go completely out.
Initial Diagnostics: After disassembly and visual inspection, nothing looks inherently wrong (No bulging capacitors, no blown resistors, no cold solder joints). In case there were any bad solder joints, I went over all the connections with an iron and new solder to no effect. Strangely enough, the monitor seemed to work for a longer period of time outside the plastic case (tested for ~1hour), and if I put the case back on then the backlights would go out within a few seconds. This oddity originally made me think it was an overheating issue, though I have not been able to confirm this.
Further Inspection: Taking measurements from the power section of the board shows that fuse, bridge rectifier, and both the 5V and 16V output are good and stable, as well as the 5V output after the optocoupler. This leads me to believe the problem resides in the inverter section of the board.
The fuse on the inverter sections gives a resistance reading of 0.2 Ohm, so it is still good. I also get a good 5V and 16V from the output of the schottky diodes. I will further go on to describe individual components for the inverter section.
Resistors: (measurements taken in circuit, so some measurements may be inaccurate)
Code:
Identifier nominal measured R818 270 Ohm 264 Ohm R819 10 KOhm 9.94 KOhm R817 10 Ohm 10.3 Ohm R816 10 Ohm 10.4 Ohm R823 10 KOhm 9.55 KOhm R824 2 KOhm 1.984 KOhm R822 10.5 KOhm 10.01 KOhm R825 270 Ohm 265.7 Ohm R4 680 Ohm 674 Ohm R11 820 Ohm 728 Ohm R6 680 Ohm 675 Ohm R29 820 Ohm 725 Ohm R16 470 Ohm 461 Ohm R24 470 Ohm 467 Ohm
Diodes:
Code:
Identifier Voltage Drop ZD801 0.69 V D9 0.556 V D2 0.556 V D8 0.554 V D4 0.555 V
Capacitors:
I have not been able to take accurate measurements of the capacitors with my multimeter (likely because they are still in circuit), but these are the following capacitors. The caps look fine visually, and I have not replaced them; however I will likely replace them soon just to be sure.
4, 470uF 25V 105 deg Su,scon (which can sometimes be a suspect brand)
2, 680uF 25V 105 deg Samxon
2, 1000uF 25V 105 deg Lelon
Transformers:
There are 2 SPW-106 inverter transformers with 6 pins for the primary windings and 2 pins for the secondary windings. Each of the primary winding on the transformers give readings ~0.3 Ohm - 0.8 Ohm. The secondary windings give readings of ~450 Ohm. The primary to secondary measurements give and "0.F" or open circuit, which is what is should be. (Correct?). If the transformers are bad, does anyone know where to find replacement transformers? I have looked and the best I can find is a SPW-105 on ebay. The SPW-106 I found does not have the same pinout as the ones on my board.
My final thought was that the PWM controller for the inverter section might be bad, but I have not taken it to the lab at MSU to check with an O-scope. It is an INL837GN, which is relatively easy to find a supplier, however extremely difficult to find a datasheet. The closest thing I could find was this schematic.
I would love to hear your thoughts on what my next step should be. Thank you for your time and effort.
-Pat
Attached Files
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