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Dead Mainboard

MontysEvilTwin

MontysEvilTwin

Well-Known Member
This may have relevance to a recent thread here. I just bought a HDR-FOX on EBay for £22.49 incl. delivery. Don't get too excited, it has no remote, no hard drive, a couple of dinks in the case, and it does not power up. But I knew this and bought it for spares. I thought the power supply had probably died, but there was no sign of bad capacitors: the power supply is now working fine in another unit. The front panel board is also working correctly. I had a good look at the main board: a component, designated U21 on the board has blown. This is quite close to the power connector, and is tucked away under the hard drive in the bottom left hand corner. Here are some photos:

U21_blown.JPG
Blown component at U21

U21.JPG
Good component at U21

U21_code.JPG
U21 Component showing code

From what I can tell, the component (Z1073A) is a voltage regulator. It is only has eight pins (well spaced out) and I think could be replaced. The most difficult part would be removing it without damaging the connectors on the board: desoldering braid should make this possible. I don't need to fix the board, but I may have a go if I can find somewhere that sells the part in fewer than hundred quantities.

This fault might not be relevant to anyone else: other dead main boards may have completely different failed components, but this could be a common fault. On other dead boards the same component may not have failed so spectacularly, making it harder to spot.
 
Mucking about with this is beyond the capabilities of amateur equipment IMHO. You need pro. kit.
 
You are probably right. I've done a fair amount of soldering and think I could fix it, but it would only take a small mistake to ruin the board. A skilled TV repair man (if you can find one) would be able to repair it. I don't need the board anyway so I doubt I will attempt to fix it.
 
I've done this kind of thing - it is perfectly possible on 0.05" pitch SOICs (which is what that Z1073A is) with hand tools. The key is that the contacts are out in the open and not too fine. Packages like PLCCs or worse BGAs (where the solder joints are underneath the chip) or PQFP/TSOP (where contacts can be much finer than 0.05" pitch) are too difficult with a hand soldering iron, but most (not including BGA) are amenable to inexpensive hot air tools. The saving grace is the solder resist layer on the PCB - without that it would be almost impossible to do this kind of rework without creating short circuits.

Many years ago I was fault-finding a bespoke computer system on a military base at a weekend. A 20-pin SOIC bus driver had failed (well, actually, I blew it up) and the only way to make further progress with most support "gone home" was to switch a chip from a less critical function. Necessity is the mother of invention and there was little to lose. I took a break and went into the local town, and came back with a pack of fine dressmaker's pins. I cannibalised a biro as a handle and melted the end around the head of a pin, then formed a small hook on the sharp end. I now have a set of dentists' pick type tools in my kit, but I'm not sure my eyes would be up to this kind of thing any more.

Once as much solder as possible is removed with solder wick (much better than a solder sucker, unless you are trying to clear a hole), the SOIC leads can be lifted one at a time with the hook while applying the iron until the chip is free.

The destination PCB pads and the chip leads need to be absolutely free of solder (other than a very thin plating) - otherwise the chip won't sit flat on the pads. The chip can then be tacked in place across the diagonals and then soldered all round. If you can, finish off with a blast of hot air - it re-flows the solder on all the contacts simultaneously, which clears any shorts and floats the chip into the centre of the PCB footprint by surface tension. Bleep around the pins to check for any remaining shorts.

But, as you say, the problem will be obtaining a replacement part (one of which went in the bin recently).
 
Can you not snip the legs to remove the chip and then unsolder the legs from the board individually? You will need some fine cutters though.
 
You would need some very fine cutters, and as such the jaws would not be very strong. It is an approach I have used with 0.1" pitch DILs with plated through-hole PCBs when the solder wouldn't let go.

A milling bit on a dremel (note use of lower-case "d") could work.
 
Trev said:
Are you accusing me of being a complete ignoramus? That's why I said fine snips.
Click to expand...
No, but I have no knowledge of your knowledge.
Show me a picture of a pair of snips fine enough to do the job then, with a size reference in photographic form, and I might believe you.
 
As I said above, I don't think it is an easy repair and it could go wrong: not for the inexperienced solderer. A lot of components on the board would be impossible to solder by hand; the pins on this one are relatively well spaced and the fact that they sit on the board, rather than go through it make it easier. If I were to attempt it I would clip the pins first, as suggested by Trev and use desoldering braid to wick up the old solder while carefully heating with a fine tipped iron to free them. As long as this goes smoothly, leaving clean contacts on the board, replacing the component should then be feasible.
When this component fails it kills the main board, and there have been a few reports of dead HDR-FOX T2s where it is the main board that is the source of the fault. I was wondering if failure of this component was a common feature in these faults.
 
One of my colleagues, who's very good at this sort of stuff, bridged all the pins on each side with excess solder, then removed it all in one go with braid.
But he has proper tools and optical aids to help do the job.
 
That's a good tip, which only works because of the solder resist coating. But like I said, it is do-able with improvised kit and I didn't need optical aid at one time.
 
AOZ1073AIEven a good pair of Swedish steel cutters are probably too big to cut those legs, so, I would go for a mini drill to cut them
To minimise board damage, I think that a solder sucker is far better than braid for desoldering.
(no I am not talking about a professional continuous suction iron, just a spring-loaded button release type).

Refitting... well a bit of glue or double sided tape under the device will keep it in the right position during soldering.
And, you are going to need a pretty fine tip on your iron for this.
Resoldering and using braid to remove excess solder can be quite effective (here the sucker would be too effective!).

But I agree with BH... these days I would definitely need optical aids.... and maybe a steadier hand.

But it does look like your biggest problem will be finding a a part (or even finding enough about the part to start looking for a replacement). My best guess was Alpha & Omega Semiconductor's AOZ1073AI, but no detail other than "4.5V-16V 3A SYNCH EZBUCK" (but you probably found the same since you mentioned quantity orders).
But there is always the concern that it has taken any other parts with it.
 
Black Hole said:
You would need some very fine cutters, and as such the jaws would not be very strong. It is an approach I have used with 0.1" pitch DILs with plated through-hole PCBs when the solder wouldn't let go.

A milling bit on a dremel (note use of lower-case "d") could work.
Click to expand...

The chip's knackered anyway, so why not use cutters/pliers to mash the plastic to pulp, brush the debris away, and with a bit of luck there'll just be the eight legs left.

(Also I could never get braid to work well and it took too long (heat transfer - I was usually trying to recover the parts). I always use a sucker these days.)
 
I enjoyed this thread but identify with Black Hole on eyesight. There was a time when I built a teletext decoder from ICs, a NASCOM micro computer [20s] and twenty years ago a TOS strippler (using it now) but now things get trying dropping reading glasses on and off whilst soldering, focus going in and out and hoping for the best.....
 
The IC may well be stuck to the pcb during manufacture. The best way to remove it is one leg at a time. Use de-solder braid to remove the majority of the solder then heat the individual pins with a fine tip and use a pair of fine tweezers to bend the heated leg upwards when it is free.
 
Before replacing it you also need to find out what caused it to expire in such a spectacular way.
It is likely a capacitor(s) has failed, if it is anything like the Panasonic freeview box regulator failures.
 
I have just been reading a product spec about a new chopper-stabilised instrumentation amplifier from Microchip. It comes in an 8-pin MSOP (micro small outline plastic) package and is 3mm square with leads on a 0.65mm pitch (approx 1/40")! Shiiiit!!!
 
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