Only somebody who has had suitable training should undertake this repair.
The Toshiba RD100KB is a tv freeview tuner with a 320 GB hard disc and a DVD recorder built in. This is not a HD unit.
Just after the 12 months warranty ran out, the unit failed. The fault symptom was that you could not turn it on. On applying mains power there was a click followed by another click a second later.
I was not keen to scrap it especially when it has some recorded programs on the hard disk that had not been viewed. After having unplugged everything, including the mains supply, I removed the cover. I could see the power supply area and this had extra plastic safety shielding over parts of it.
Further disassembly revealed a complex power supply arrangement with multiple output dc voltages. I could see that one section of the power supply was permanently connected to the mains input and this produced a 5 volt rail. Pressing the “power on” button caused a relay to close a pair of contacts on the power supply board and produce the multiple dc outputs require for the logic and various devices. As I said the relay only closed the contacts for a moment and then dropped out again. I decided to entirely remove the psu board from the unit and this meant disconnecting quite a few ribbon cables and some mechanical disassembly. Once I had got the psu board onto a flat and non conductive surface, I applied a link to short out the relay contacts. This meant that mains would be applied to the main power supply and I could chase down the fault. It seemed that the power supply would only work properly when the other bits were connected as a load. However I was able to determine that the 12 volt rail was missing with everything connected.
After breaking everything down again, and with the mains supply unplugged , I probed around the 12 volt supply components looking for short circuits. Indeed there was a short circuit. I removed a capacitor as they are the usual suspects, but this was not the problem. Cutting a track threw suspicion upon a couple of Schottky diodes that were in parallel. I de-soldered the end of one and lifted it. The short circuit disappeared. This particular diode was a short circuit. The diode is a SK3B and is D2204 on the board. I tested the board again with just the remaining diode in circuit. It was now working. I re-assembled everything and removed the link from the power supply board.
A functional test showed everything in working order. The Schottky diode has a 3 amp rating and as there were two in parallel they must be expecting currents of up to 6 amps. For this reason I ordered some replacement diodes so that I could change them as a matched pair.
It was pleasing to get this unit working again. Modern electronics are usually reliable but there do seem to be a lot of fake components around these days.
This experience makes me wary of Toshiba products. It was certainly not designed for ease of servicing and I could not get hold of a circuit diagram.
Personally I prefer to see a proper mains earth for the metal case.
Peewit
2 comments:
I have had the same problem with this product, twice. Got it fixed at the cost of €60 only for it to fail again
Both times I left the DVD tray open overnight, forgetting to remove the DISC and closing the tray, and the next morning the unit has died.
It seems as though it is drawing too much power with the tray open and these is no logic built into the system that says if the tray is open and the unit is idle to close the tray and go into standby mode - this is what happens on other DVD units that I have.
Have you had much experience from other owners of this unit?
Does anyone know where these diodes can be purchased and is there an equivelent SK3B
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