One for electronics techies

[Alan Zoff]

This query should really be for a dedicated electronics forum but I thought I would try here first as I know some members have a lot of relevant knowledge.

Our 6 years old Panasonic LCD TV which we brought over from the UK developed a fault on the main PCB which will cost more to replace with a new PCB than the TV is probably worth. But it has been an excellent TV with a superb picture. I have tracked down the problem to a small voltage regulator. Farnell in the UK told me the original Sharp component was obsolete but they supplied an "equivalent" for next to nothing. However, in addition to the fiddly soldering required, the new part has 4 long pins, 2 either side of a middle short pin that seems to float in mid-air, whilst the original has 5 long pins, all soldered to the PCB. Farnell seem unwilling to offer any advice on what happens to the middle pin, no doubt concerned about liability. The Panasonic guy who identified the (apparently common) fault was obliged to suggest I obtained a very expensive new panel or engage the services of an equally expensive engineer.

Anyone know/have useful suggestions? As you will have gathered, I am not an electronics person myself but have successfully repaired circuit boards in the past when supplied with good advice and am aware of safety issues when working with TVs. Spending £100 plus on a new PCB or a professional repair seems excessive so I am willing to play with the existing one if the alternative is to dump the set.

[Chancer]

What is the regulator number?

 

With that we can find the pin out détails, I'm very rusty as it's been close to 30 years since I was developing electronics and was self taught then but it should come back, IC regulators are fairly simple things and if it is an equivalent the pin outs will be the same, you probably just need to push it further down through the PCB so that they can all be soldered, certainly diodes and LEDs always have one leg longer than the other so the anode can be differentiated from the cathode, if you reverse bias a diode or IC it will kill it, I cannot even recall which has the long or the short leg, told you I was rusty!!!

[Alan Zoff]

Thanks Chancer.

The original (apparently obsolete) part is Sharp 070XZ1H

The Farnell replacement is ROHM type BA00BC0WFP-E2

[Chancer]

Here is a link to the data sheet:

 

http://www.mouser.com/ds/2/348/ba00bc0wfp-e-210256.pdf

 

Your old IC was a TO220FP-5 package and the new one is a TO252-5

 

One one it is a ground pin and on the other its an NC pin but I dont know what that means [:P]

 

Looks to me that the required ground connection for the centre hole on your PCB should come from the casing of the IC, that is usually done by it being screwed to a metal chassis or heat sink.

 

I would use a continuity tester to see if you have continuity between the centre pin stub and the metal casing, if so then you can just solder the pin to the PCB, if not then you will have to attach a piece of wire to the casing using a tiny, probably M3 nut & bolt and solder the other end to the centre pin hole on the PCB.

 

My descriptions are usually confusing, hopefully it will make some sense when you look at the data sheet, seems like you were wise to seek advice.

 

[pip24]

I think NC on an IC means Not Connected.

[richard51]

Just a thought but there are lots of panasonic pcbs available on ebay.

Even experienced electronics technicians working in the field full time (for good companies) don't/rarely go down to component level nowadays.

[AnOther]

Relative pinouts here

[img]http://i.imgur.com/cBceHVk.jpg[/img]

[Alan Zoff]

Thanks all. I will have a play and see what happens.... As I said, nothing to lose, as long as I don't damage anything else in the process.

I suspect I will end up buying a second hand board which it seems can be had for around £35 on Ebay uk which I will be happy enough to pay if the set is restored to its previous performance.

[Chancer]

The IC will work, just ignore most of what i said and follow this extract:

 

you will have to attach a piece of wire to the casing using a tiny, probably M3 nut & bolt and solder the other end to the centre pin hole on the PCB.

 

[Alan Zoff]

Noted. Many thanks.

[Alan Zoff]

Just as an update, I tried to fit the new regulator but the miniscule soldering requirements were beyond my skill level - and I probably needed a much finer iron. But worth a try.

However, a reconditioned PCB arrived very quickly for the reasonable £30 outlay and the set is restored to perfect condition. I had brought it over to UK for the repair and it will be back in France shortly. I hope it won't be needed but I will hang onto the faulty board as a source of possible spare parts.

Thanks again for the expert comments and advice. I learn a bit more each time.

[AnOther]

Fair play for having a go but believe me that ain't minuscule !

[Chancer]

He is right but you need good vision, a good small powerful temp controlled soldering station and a desoldering pump, all of which I once had, 20 years ago I worked on stuff much smaller but now [:(]

 

Good vision is but a memory, my decent soldering iron is in the UK, the Lidl one I use here is just too clunky and not enough heat, got a desoldering pump though but its the vision which is the biggest handicap, good on you for having a go, after a try like that we usually dont begrudge the price of the new board, in fact often appreciate it.

[AnOther]

I've replaced many a surface mount IC in my time and still have some of the gear to do it with somewhere but as Chancer says eyesight becomes the limiting factor and these days I find myself struggling even when working with full size components [:(]

I recently had to replace the micro USB connector on the motherboard of my tablet, a job which in former times I'd have expected to be done in one pass and take maybe 10 minutes start to finish but this time it took me half an hour or so to get a result I was happy with.

[img]http://i.imgur.com/0jCIQH7.jpg[/img]

[Pierre ZFP]

I've just bought myself some magnifying glasses from Amazon

I haven't had the chance to use them in earnest yet but I though for 4 quid they were worth a punt. Seem to be made OK and the lenses are acceptable for the short times I will be using them.

Is it just me or does anyone else have difficulty reading the colour bands on 1/8 th watt resistors?

[AnOther]

I'd be interested to see what the actual focal range of those are.

I've got 5x, 15x, and 20x loupes and in practice it's only the 5x that's really useful because it has a focal range of about 2" whereas the 15x is only about 1/2" and the 20x is about 1/4", both much too close in to do any work.

[Pierre ZFP]

Yes I was wondering that.  Unfortunately the glasses are in the UK at the moment and I'm not. I should get my hands on them in a week or so, I'll report back...

[Chancer]

The focal distance of my bionic left eye is the length I comfortably work at with bent arms, like typing this computer and reading the screen, the depth of field is shallow, only about 6", they calculated it pretty well IMO considering they only had the damaged remains of an eye to work with, no possibility of doing eye tests etc after the accident.

 

The depth of field is the problem I have with reading/close work glasses, at my correct prescription it is so shallow, a couple of inches its better to wear my older reading glasses that have less magnification.

 

I have a X8 loupe from my drawing office days in the late 70's, still gets a lot of use but you have to place it on the object and stick your eye to it, I also have a soldering aid called "helping hands" that has a built in loupe which I never needed to use when i was doing electronics, it would probably help a lot now.

 

Like many things in life you just dont appreciate something until you lose it or lose it partially.

[Alan Zoff]

As someone who is now seriously deaf, I can empathise with that last comment.

My problem was not so much my sight but with pin-pointing the solder contacts with an iron that was OK when putting together a Heathkit radio in the 70s but a little clumsy for a modern TV board. It would have been fine if the idea was to solder 3 pins with the same blob (to use the technical expression).

[Chancer]

Heathkit!!!

 

That brings back memories, my temperature controlled soldering station (which is packed away in the UK and never available when I need it for fine work) was a Heathkit kit [:-))]

 

You can get fine points for the DIY soldering irons, my Lidl ones have them but they are such a poor fit for something that is supposed to conduct heat that the iron is in contact with the joint for longer than the IC should really be heated, the ideal is max power minimum contact time which I can do with my Heathkit setup.