Unmarked component

[Mark56]

Any more ideas chaps, please.

 

[Resqueline]

Sorry for not replying sooner.
With no motor connected there's nothing to blow the MOSFET exept the (shorted) diode.
I'm quite sure that it must have been damaged somehow from the previous failure.
Even if the MOSFET failed first it would not have damaged that diode.
I can't imagine there's a short inside the relay.

 

[Mark56]

Thanks for getting back to me. I shall have a close look at the relay and surrounding components before trying again. I think I mentioned earlier in the thread that it was due to my own error that the original Mosfet had blown as I connected the AC supply to the motor connection. Is that likely to have blown the diode and could it have damaged anything else before the fuse blew.

Would you be able to do me a huge favour if I pay you by PayPal to send me replacement parts. Spain is so far behind with on-line ordering so I have to get parts sent via a UK address as I have not been able to locate a supplier (that keeps Mosfets) in the UK that will ship direct to Spain. Or, do you know of an electronic component supplier that will ship direct to Spain, will have the Mosfet I need and will deal with one off orders.

 

[shrtrnd]

Sure hope you guys got your device right.

 

[Mark56]

Is there a chance that Resqueline had got it wrong shrtrnd?

I'm in your hands.

Would I be cutting out all the doubt, if there is any, if I purchased the component identifier mentioned earlier to use on the mirrored component at the other end of the circuit board? Taking note that that component supplies a higher voltage motor.

 

[shrtrnd]

We haven't seen the circuit.
Everyone is trying to help.
Considering the problems you're having. I would be seriously trying to get some
information from the manufacturer. If you know who made the chair, you might be
able to track down who made the circuit for it, and find information on the circuit.
If not from the manufacturer, then a Google-type search for anything anyone else
has posted on this type of problem with that manufacture chair.
You are probably not the only one who has run into this before.
Frankly, most of the guys I've seen on this site are pretty good, especially when
they've got a picture of the board in question. But a schematic of the circuit would
almost certainly get some good responses.
If your load for this circuit is damaged. No matter what you do to repair the driving
circuit, you are going to fry any components in it that you replace.
That MAY be your problem you know.
Good luck on this. You seem determined, and people on this site will help as well
as they can, cause we have the same mind-set you do about fixing things.

 

[Mark56]

Thanks for the tips.

I am trying to find out who the manufacturer is but meanwhile all there is are the photo's of the board earlier in this thread. After replacing the Mosfet it burned out without any load connected to it.

The chair has no makers label and even the instruction manual has nothing but the instruction in it, no name of a manuafacturer just a model number TS898. I am exchanging emails with a supplier of the chair who might be able to put me in touch with the actual company that built the chair but I will have to waite and see what happens.

Seeing as the maker of the board removed the part numbers off most of the transistors I think it will be unlikely they will disclose what the transistor is.

Does anyone here have any doubts about the transistor being an N-Channel Mosfet or could it be something else?

Would it be worth my while to get the Component Identifier mentioned earlier and use it on the matching component in the working board I have in an identical chair?

 

[Resqueline]

Looking at the pictures of the circuit board you hardly need a diagram. (I'm on vacation now and can't easily make a drawing.)
The motor driver output is exceedingly simple; 1 transistor, 1 protective diode, 1 polarity changing relay, & 1 R-C snubber.
When applying transformer AC to the motor output connector - the diode would short the transformer every half-wave and would likely fail.
I'm sorry I forgot to mention checking this diode in the beginning (I guess I take it for granted to do such things).
Farnell has a Spanish office and they sell one-off's, but I'm not sure about their non-business customer policy.
Elfa does not have a Spanish representative but sells one-off's, also to non-business customers, and have no export restrictions to any countries as I'm aware of.

 

[Mark56]

Thanks for the added help and the suppliers URL's. Elfa looks like they are going to charge €20 for delivery so I'll have a look later at Farnell and see what their delivery charges are like.

One thing that confuses me is the identical circuit on the other end of the board supplies a higher voltage motor. What is it that regulates the voltage down to 24V on the damaged end?

 

[Resqueline]

RS-components also seems to have a Spanish office.

As far as I can tell the circuit at the other side gets the same voltage, although via separate diodes & capacitor.
The motor may intentionally be run at a lower voltage than it's spec'ed for.

 

[Mark56]

The output from the matching transistor circuit is 35V, see second post on page 2 of this thread, unless I made a mistake when I measured it.

Thanks for finding the RS spanish office, if they charge for postage at the same rates as the UK office that will be very usefull.

 

[Resqueline]

Ok, but in your first post you also measured 35V on the broken transistor, and I've not noticed any indications to there being a difference between the two sides.
It's not uncommon for (relatively) low-power supplies to have a quite high off-load voltage, and motors are forgiving.
But the transistors may even be driven with PWM to compensate for a high supply and thereby giving a 24V average.

 

[Mark56]

OK, thanks for that confirmation. I'm now going to have a go at RS in Spanish.

 

[Mark56]

Thanks again for the RS spanish link. Order placed successfully. Still €12 for postage but thats better than Farnell or Elfa buy a good few quid.

I'll let you know what happens next.