Hyundai HLT-3270 Repair
I recently got a 9 year old HLT-3270 32" LCD TV and thought it would be worth fixing.
The Defect
TV will not turn on, no power LED on, no current draw on the mains supply. Mains fuse on the power supply is open.
Power Supply BP-170AWL
This set uses a Bentek DMC BP-170AWL power supply according to the sticker on the circuit board. I was not able to find schematics on that particular board. It provides only 12V and 24V to the TV main board and backlight converters and the output pins are labeled.
Key parts:
- PFC controller: Fairchild FAN7527B
- PWM controller, switch Fairchild FS7M0880
- Diode for PFC STTH8L06 (assumption)
Datasheets can be easily found. The FS7M0880´s application note AN4121 ist particulary interesting.
The TV can simply be powered by applying 12V/1,5A and 24V/5A which I tested with lab power supplies. That could be an option if the original PSU cannot be repaired.
Power Supply (after swapping some caps)
I tested the rectifier, diodes, the PFC´s FET, and the power switch for shorts. All capacitors where at least not shorted. Then I supplied PFC and PWM controller with an external supply voltage and found the current draw of approx. 20mA ok. After replacing the fuse, I slowly powered up the device with a 60W light bulp in series. It turned out that the power supply tries to start up, fails and retries several times per second. When measuring the PFC controller´s supply voltage with a scope, I found it really unstable, rippling between 12 and 25V.
Solution
The instable internal supply voltage was caused by a defect capacitor: C19 100uF/35V. After replacing that one, the power supply got in some more stable state.
I then checked further caps and found all Samyoung branded ones out of spec. In the end I did replace:
- C13 47uF/35V
- C14 1uF/50V
- C19 100uF/35V
- C32 1uF/50V
- F1 T3,15A
Again, these caps were all dead or got far less than their original capacitance!
No semiconductor parts were obvious damaged. I did not care about most of the capacitors on the secondary side - although they are Samyoung types and might not be in good condition too.
After the repair, the set works fine again. The power supply got a standby power consumption of approx. 10W which appears a bit too high. Possibly there is still something wrong with the standby/burst mode?
