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Spoiler alert: One pic at a time if you like quizzes.
Servis. 5 years old approx. No motor action. Bosch motor – one brush half the length of the other (Why???) but still 10mm left on it. Customer tells me m/c had already had board replaced one week into its life but had been OK since. (Could of done with knowing that before starting work as it would have helped not to have been baffled by the burn mark on the plastic, but anyway.)
Brought board home, went through checking all triacs, relays, resistors, transfromer, coil, diodes and then noticed something strange.
So here’s a little quiz. If you enjoy quizzes, don’t scroll down until you’ve had a good look at the first picture of this module (rt) with an old, vaguely similar one on the left.
Brushing away some carbon dust, I finally noticed this:
(At that stage, I hadn’t got the second module out to compare, so I was a bit baffled as to whether there had been a component there or not.)
So my question is, and I don’t expect anyone to be able to answer it with any degree of certainty, what caused it and will any other parts of module or machine be damaged?
I’ll be replacing VR1 and going back to try it but just thought I’d have some fun in the meantime. BTW, one wire to the ntc had come out of its connector and the earth wire terminal at the motor had broken (bad design making it shorter than the other wires.) so I guess there might have been an o.o.b. situation.
The back of the board shows VR1 is between L & N input to transformer, lower left of this pic:
Mike.Re: Spot the difference. Or one of them. Simple pcb repair?
the component is a vdr (voltage dependant resistor). its job is to soak up voltage spikes to stop it damaging other components. most of the time you find them across mains triacs. since a triac would get damaged if the voltage went above 600v or so the vdr conducts to let the spike drain away. if they go faulty it depends on the job they are doing what happens. if it is across a triac then the vdr bypasses the triac turning on the component such as a valve etc. if they are across the mains they go with a bang. in your case you will probably find live and neutral to the board are either side of it
Dave
Re: Spot the difference. Or one of them. Simple pcb repair?
did not read your post properly as you say it is across L&N so its gone short and went with a bang. from what i can see of the board reverse they have narrowed the print to act as a fuse in case this happens
bad news. since it is only a safety component it is unlikely to cause your no motor fault. although when it blew the resulting spike may have caused the problems
Dave
Re: Spot the difference. Or one of them. Simple pcb repair?
electrofix wrote:from what i can see of the board reverse they have narrowed the print to act as a fuse in case this happens
That’s clever stuff. Didn’t notice that.
The machine fills and empties.
The thing along to the right (footprint seen from reverse of board) is an LM7805. IIRC that’s a voltage regulator. Maybe I should check it? Would it be likely to have popped?electrofix wrote:bad news. since it is only a safety component it is unlikely to cause your no motor fault. although when it blew the resulting spike may have caused the problems
Dave
Well, I have to admit I didn’t think to check the motor for shorts etc., just assumed it would be OK. Guess I’d better check that when I get back before putting in this or another module. Looks like I may have to see what EMW have available. Already told customer it might cost that and she’s OK paying up to about half cost of a new machine. Economic situation these days seems to be stimulating business just a little bit.
Mike.Re: Spot the difference. Or one of them. Simple pcb repair?
think thats a 5v voltage reg. would expect other things apart from the motor not to work if thats gone.
as for motor short not sure on servis what would happen. on zanussi it give you a fault code.you would have to trace motor circuitry but unless there is a relay failure it may be a new board
long shot have you checke tacho continuity ?
Dave
Re: Spot the difference. Or one of them. Simple pcb repair?
Dave is right that RV1 is a VDR but to me it looks like it has either been cut off or vibrated off as the tend to leave decent scorch marks when they go pop.
Yes a 7805 is a 5V voltage regulator and is probably providing power to the microchip(s) – if you want to check it then looking from the front it is power in (needs to be approx 7V plus ideally), ground, 5V out put – if it helps when testing it then the tab is also ground.
It would be worth having a check of all the large resistors as they are of the fusible type and can fail open circuit silently.
Jem
Re: Spot the difference. Or one of them. Simple pcb repair?
Well I went back earlier this .., yesterday evening, and left it all spinning nicely after some stressful fault finding. Had soldered in the VR1 from the other board and, just as Dave had predicted, it didn’t make a jot of difference. So, following his and Jem’s guidance, I looked again at the motor. And across the brushes (which I had renewed on the first visit) I was getting a rather high reading at most points as I turned the rotor. So I thought maybe they just needed a bit of bedding in or maybe one was sticking. Did that but still no go. Thought I would have to dismantle the motor to find out which wire went where as they were all (eight) light blue and disappeared into obscurity. Then I remembered something about Servis modules being prone to edge connector problems so I squeezed and picked around with sharp point, all to no avail. Finally I did some more basic checking and found the problem.
There was a pointer, maybe two even, there in my first post but I had overlooked it. If I just told you what it turned out to be, you would just read it, say oh yeah, and move on rather than using your brain. Wonder if you can guess what the problem was and find the evidence that pointed to it?
Mike.Re: Spot the difference. Or one of them. Simple pcb repair?
Had the same fault on a servis no motor but would fill and empty!
after an exhausted checking sending board off for repair! that turned out to be in the end as the motor built in overheat cut out on the windings oc!
Am i correct do i win a prize? 😀Re: Spot the difference. Or one of them. Simple pcb repair?
Sorry, you are warm but not the winner this time round :cry:. Please have another free go 😀 as your experience is a useful addition to the list of things to check for anyone else who reads this thread, having encountered the same fault.
Mike.Re: Spot the difference. Or one of them. Simple pcb repair?
Not the connectors in the plug that connects to the board…? One looks to have taken a bit of heat there.
George
Re: Spot the difference. Or one of them. Simple pcb repair?
Sorry George, not this time.
Dave was on the ball when he said,electrofix wrote:
you would have to trace motor circuitryDave
Which I did. But what did I find? The clues (textual, not pictorial) were there in my opening post (together with a few red herrings, not intentional you understand) but I didn’t make the connections at the time. I’m wondering if I’ve made this too difficult. It’s nothing excitingly different from what commonly happens (though we don’t always find it) and I have very probably BER’d a good few machines in the past for not keeping clear and logical when times get tough.
Mike.Re: Spot the difference. Or one of them. Simple pcb repair?
So you replaced the motor and the board?
George
Re: Spot the difference. Or one of them. Simple pcb repair?
Yes, of course, I always keep a spare Servis Bosch motor and selection of Servis boards in my bag 😆 .
Here’s a huge clue. Had I replaced both, the fault would still have been there.
Mike.Re: Spot the difference. Or one of them. Simple pcb repair?
Ok, without being there and testing it .. It could be anything .. Broken wire, bad connection, defective loom plug, defective pressure switch, defective heater.. And the list goes on.
George
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