Bush LCD32TV005HD PSU blown, no picture after PSU fixed

[wellij81]

Hi,

I wonder if anyone can help please? I have a Bush 32" LCD which had a blown PSU (24V rail gone, 12V ok.) I suspected the switching control IC, so I swapped them (same IC on each rail), so now 24V ok, 12V gone. Using a bench PSU to supply the 12V rail, it responds to remote control by flashing the red LED and the PSU control line goes in and out of standby in response to the remote, but there is no picture and no on-screen menu. The backlights work and the supply rails are ok. I haven't been able to find a manual, so it is hard to fault-find the main PCB. Has anyone got any tips?
I have read other posts about the LCD panel connector being dodgy, but I have reseated that. It all looks ok, no burnt bits, no bulging caps, but something must have taken out the PSU.

Thanks,

Jonathan

[tv tony]

i have one on the bench at the moment, there are two versions, one with the audio out on the psu, one without, which is yours?

[wellij81]

Hi Tony,

Thanks for the reply - I was beginning to wonder if anyone was out there! Mine has the audio out from the main PCB, not the PSU. The PSU says Beko Z1J.194-04. The main PCB says Beko Z1J190R-6. I have downloaded the service manual from this site. It seems to be the same as the Beko LM chassis. I have checked all the regulators on the main PCB and they are all producing the correct voltages, such as 8v, 5v, 3.3v, 2.5v and 1.8v, which is a bit worrying.
Any ideas?

Thanks,

Jonathan

[wellij81]

Some progress. I removed the upper chassis plate to get to the LCD driver PCB, and found a burnt 100 ohm resistor and burnt smd diode. I didn't have the right diode so I bodged two 1N4148's onto the PCB and replaced the 100 ohm resistor. To my amazement I got a picture! Unfortunately the 24v side of the PSU gave up so had to run both rails from bench PSU's, which caused the backlights to flicker probably due to lack of current from 5A PSU. Even so, I got it to tune in a station and got pictures and sound. Now all I've got to do is fix the PSU. The LCD driver board is available for £55 from SJS, but hopefully the bodge will last.

Jonathan

[tv tony]

well done but the diode is a zener that hols the supply steady, there is a 5v screen and a 12v used, i would fit one pronto, the last thing you need is a lcd drive pcb giving up on you
regards

[wellij81]

Thanks for the info Tony, you've got me worried! I've taken it apart again to have another look. The ident no. on top of the smd diode is KJH. A Google search for 'smd diode kjh' brings up two datasheets, for BAV70 and MMBD7000, both of which say they have kjh as their marking! They are both standard small-signal switching diodes, pretty-much equivalent to 1N4148, although the MMBD7000 is an accurate match for the pinout. The good thing is it isn't a zener, so must be another diode that you've had experience of going on that board? The 100 ohm is circuit ref RD53, but I can't read the diode ref. Unfortunately the manual I downloaded does not include the lcd driver circuit.

Thanks again,

Jonathan

[wellij81]

An update for those trying to fix these PSU's. I bought a new controller IC and FET for the 12v side but was concerned when the 12v rail went up to 14.9v and the 24v rail didn't come up when on a dummy load. Spent ages testing the low voltage side, and eventually came to the conclusion that the "12v" side of the PSU is designed to produce 12v in standby and 15v when fully on! The 24v rail was also ok really, just me being cautious. It will not start with a dummy load, but the TV has a longish time-delay on the backlights so it doesn't have to start up under load.
So everything is ok now.
For anyone trying to buy the controller IC (type ICE1QS01), most suppliers seem to charge around £10 for it, but Littlediode do it for £2.85 (+VAT and post, but still much cheaper). It seems like a genuine part and works ok.
I have drawn out the PSU circuit by hand as it isn't in the manual. I may scan it and upload it if anyone is interested.

Jonathan