Techwood are another “faceless” brand of TV that are Vestel made, they are sold at Morrisons, we have done a few of them. Recently a customer brought her 32″ Techwood TV to our workshop, saying there was power, but no picture or sound, and the LED blinks. Normally on a Vestel mainboard the LED only blinks during Over-The-Air firmware update, so she left it with us, and we took a look under the bonnet.

Techwood-32832-under-the-bonnet

It uses a Vestel 17MB25-3 mainboard, similar to my 16″ Linsar 16LVD4.¬†Another common cause of a blinking LED on a Vestel can also be the inverter. Often on these separate inverter TV’s, if the inverter chip, a MOSFET, or indeed the coil (some have 1 some have 2), are faulty, the error reporting circuit built into the main chip on the inverter relays this info to the processor and the software goes into protection mode, preventing the set from booting up, causing the flashing LED.

A blinking LED in any other case than firmware update is mostly a power supply issue, but here’s our checklist:

  • Check microfuse FS105 on main board, near CAM module.
  • Check SMD fuse FS106 (4A) for open-circuit. Check diodes D881 and D893 (UF5402) for short-circuit.
  • 24V rail might be short-circuit, disconnect inverter board supply to prove. Check and replace dual N-channel MOSFETs IC803 and IC804.
  • Replace IC830 (FAN7711 and SMD capacitor C925 (1nF).
  • Check for short-circuit between pin 6 and pin 8 of IC830 (FAN7711). Replace IC830 and SMD capacitor C833 (100nF).
  • Check and replace SMD transistor Q839 (BC859).
  • Check D893 and D891 (UF5402) in centre of PSU for short-circuit.
  • Voltage at regulator U122 varies between 4V and 9V instead of being stable at 8V. Replace U122 (LM1117ADJ) on main board.
  • Check C961 (470uF/35V) at top of PSU.
  • Check D893 and R1036 (2.2K) on PSU.
  • Replace IC830 (FAN7711).
  • Check D893 and its feed resistor. Replace MOSFETs Q813 and Q814 and IC830. Replace C828.
  • Replace C892 (100uF), C801 (33uF), C840 (33uF).

In our case, the voltages coming out of the power supply were fluctuating badly, so we knew the mainboard wasn’t the original fault. The power supply is a Vestel 17 PW26-3. So, out came our service manual and power supply schematics, and we set to work.

Vestel 17pw26-3 PSUNo obvious bulging capacitors, no burst vents, and no burn marks anywhere. The PSU microcontroller was operating, and the clock waveforms were fine. The bridge rectifier system and components were OK. The problem was the output capacitors just before the output sockets, their voltages were up and down.

Replacing C802, C934, Q828, D882 & D883 and some various resistors fixed the problem, and the TV was back up and running. The power supply even emitted less no-load whine than it did before! A lot of people might say Vestel are junk, but the thing I love about them is they’re off the shelf parts and components, fixing them is a joy. You’ll often find a lot of Vestel TV’s with all manner of screen sizes, big and small, being driven by the same boards and power supplies. The ProView panels can also be replaced with dual lamp screens from a Sony Vaio laptop if you need a 15.4″, 16″, or 17″ panel ;)

Here’s a fun fact: The 17MB25 board can drive panels from 12″ all the way to 36″ full HD, even if the TV is marketed as just HD Ready, that’s often just because the panel is a small one, so the board software goes into HD Ready mode to drive it. Connect a 32″ to it and the multiplexer goes into full steam 1920×1080 :)

Vestel? Turkish? Delight? Yeah, I would say so, cheap, cheerful, and easily fixed. Take note, Sony ;) Funnily enough Greg has a Luxor branded Vestel lined up for me with similar symptoms, I suspect it’s going to be the same routine as this one.

 

Be Sociable, Share!
Leave a Reply