Hi all,
my oldest Z-Wave module, a TKB TZ68E plug-in power switch, died recently & I've just got around to having a look why.
It appears an electrolytic cap on the power input side has leaked electrolyte and shorted itself or to the switch mode stepdown IC; there is dried gunge on the underside of a cap and a brown stain or flash mark on the PCB between that and the IC pins.
It has a 500mA T wire ended fuse in the power feed to the PSU, which has blown. The rectifier is only half wave so the two 2.2uF smoothing caps will have quite a bit of ripple.
The cap that has visibly leaked reads a few nF, while it's twin before the small choke still reads 2.2uF.
The PCB includes what looks like an 8.2 Ohm wirewound in series with the fuse - but that has a factory fitted link underneath it for some reason?
The overall device is surprisingly well made, and was slightly awkward to disassemble. The two PCBs had a set of rigid double-ended pins between them, which I initially tried to desolder - but I could not get them to separate cleanly from the board with solder wick, despite reflowing with tin-lead solder a couple of times; hence the flux mess around the holes.
I ended up cutting the pins in half and removing them individually with tweezers, then cleaning out the holes with solder wick.
I used the same method for the IC, due to the surface mount components immediately against some of the pins.
All the required parts are available from RS, so they are now on order and I'll reassemble it and give it a try once those arrive. RS don't have any 2.2uF caps with a good ripple rating in stock so I'm using 3.3uF, which are slightly bigger casings (10mm diameter rather than 8mm), but should still fit OK, there is plenty of spare space in the unit.
Photos below for anyone curious, I'll update once I have parts.
Update - the parts arrived first thing this morning and happily it works perfectly again with them fitted.
For anyone else trying to repair one of these or similar TKB modules, the screws that hold the case together are a type I've never seen before, a small triangular recess head. However a T8 torx bit works well on the as long as you keep enough pressure on it to prevent slipping.
In hindsight, the IC was likely OK and it just needed the new capacitors and fuse, plus a good scrub with alcohol to remove the crud emitted by the dead cap.
Suitable parts are (or should be) these capacitors:
And these fuses, which have the same 500mA T rating as the original but a slightly better break current rating - and ar a bit smaller so easier to fit in between the other parts.
If the IC is needed, it's one of these:
The caps above are the exact values of the originals and long life types. Those appeared to be out of stock when I was ordering so I used some 10mm diameter ones rather than 8mm; they fit OK but need to be stood away from the PCB slightly, putting them rather close to the logic PCB. I added a small piece of insulation above the caps just to be sure of no future problems. If they had been the 8mm diameter ones that should not have been needed.
my oldest Z-Wave module, a TKB TZ68E plug-in power switch, died recently & I've just got around to having a look why.
It appears an electrolytic cap on the power input side has leaked electrolyte and shorted itself or to the switch mode stepdown IC; there is dried gunge on the underside of a cap and a brown stain or flash mark on the PCB between that and the IC pins.
It has a 500mA T wire ended fuse in the power feed to the PSU, which has blown. The rectifier is only half wave so the two 2.2uF smoothing caps will have quite a bit of ripple.
The cap that has visibly leaked reads a few nF, while it's twin before the small choke still reads 2.2uF.
The PCB includes what looks like an 8.2 Ohm wirewound in series with the fuse - but that has a factory fitted link underneath it for some reason?
The overall device is surprisingly well made, and was slightly awkward to disassemble. The two PCBs had a set of rigid double-ended pins between them, which I initially tried to desolder - but I could not get them to separate cleanly from the board with solder wick, despite reflowing with tin-lead solder a couple of times; hence the flux mess around the holes.
I ended up cutting the pins in half and removing them individually with tweezers, then cleaning out the holes with solder wick.
I used the same method for the IC, due to the surface mount components immediately against some of the pins.
All the required parts are available from RS, so they are now on order and I'll reassemble it and give it a try once those arrive. RS don't have any 2.2uF caps with a good ripple rating in stock so I'm using 3.3uF, which are slightly bigger casings (10mm diameter rather than 8mm), but should still fit OK, there is plenty of spare space in the unit.
Photos below for anyone curious, I'll update once I have parts.
Update - the parts arrived first thing this morning and happily it works perfectly again with them fitted.
For anyone else trying to repair one of these or similar TKB modules, the screws that hold the case together are a type I've never seen before, a small triangular recess head. However a T8 torx bit works well on the as long as you keep enough pressure on it to prevent slipping.
In hindsight, the IC was likely OK and it just needed the new capacitors and fuse, plus a good scrub with alcohol to remove the crud emitted by the dead cap.
Suitable parts are (or should be) these capacitors:
And these fuses, which have the same 500mA T rating as the original but a slightly better break current rating - and ar a bit smaller so easier to fit in between the other parts.
If the IC is needed, it's one of these:
The caps above are the exact values of the originals and long life types. Those appeared to be out of stock when I was ordering so I used some 10mm diameter ones rather than 8mm; they fit OK but need to be stood away from the PCB slightly, putting them rather close to the logic PCB. I added a small piece of insulation above the caps just to be sure of no future problems. If they had been the 8mm diameter ones that should not have been needed.
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