Voltage converter circuit - Bosch / Siemens washing machine

There's certainly a shorted component which burned up the resistor. Resistors don't just burn up on their own.

Thanks for the email message and feedback. The problem occurred when testing the pumping out of water (which wasn't working at all - everything else seems OK). However, I have disconnected all the external connections to the motor and pump from the circuit board. Any suggestions on how to proceed with fault finding (assuming some component is shorted on the circuit board)? At present I don't understand the power supply design on the circuit board.

Best regards, Theo van der Merwe

there's likely a thermal fuse in the transformer windings. If the motor pulls anywhere close to 15A they figure your circuit breaker will do the trick. BTW fuses don't protect semiconductors, they're too slow.

Something's shorted and drawing too much current. A metal film resistor tends to be a pretty good fuse in many cases.

Less current, smaller resistor, cheaper. Also, it ensures that the transformer is not hot in the event of a fault.

The AC cannot be rectified prior to your transformer. Can't can't can't. I'm confused as to what you've got here... does the main power all run through the transformer, or is the transformer just to step down the voltage for powering the electronics with the AC going to power the motor relays? I don't think you've got any motor relays if you've got Triacs (see below).

The BTB16 is a 16A Triac, not a regulator. It's likely used to switch on the motor or pump and possibly control the speed depending on the complexity of the control circuit.

First, can you confirm that if you physically disconnect all wiring from the pump, that the problem persists? That would effectively rule out the pump. I might try powering the pump directly by attaching a line cord and confirm that it works. The triac which controls (I am assuming here, the pump MAY be controlled by a relay as it only needs to operate at one speed) has virtually no resistance when biased by the gate voltage, the only thing limiting the current draw is the load which is in this case is the pump. So let's rule it out.

If in fact the pump is fine, and if removing it from the circuit does not eliminate the problem of the resistor smoking, I'd try removing the triac which controls the pump. When triacs fail they either stop working or fail shorted. Neither of these matches your scenario. Check the pump wiring and make sure there are no shorts to ground or shorts from hot to neutral lead.

If it's a relay and not a triac which controls the pump I'd take a good look at it... are the contacts burnt? What else is around it in the circuit?

Can you confirm the writing on the 8-pin DIP? If there are various motor speeds it could be a pulse width modulator driving the triac, but I come up empty with "TP209P"... TP209 yields a DC-to-DC upconverter, 5VDC in and

Dave

Thanks for the feedback, now I understand better.

Thanks for the feedback, now I understand better.

I can send you a JPEG of the circuit board if it can help, but below is a brief description of the connections:

damaged resistor of unknown value, probably 2W from the size)

(and R1). C1 is a large 0.22uF 275V AC

Red Black Orange Red or other way round). Eventually the connection from R2 ends up at a connector at the edge of the circuit board (e.g. could be motor).

be pump/motor).

is marked -, so it could be polarised capacitor (looks like an electrolytic capacitor).

(other end)

connections marked S10 K275 0013

small components looking like surface mount capacitors)

positive, other end marked - . Looks like electrolytic capacitor 16V

is found next to the connection to the relay).

Please let me know if you need more information. The presence of a polarised capacitor C2 of 400V connected to the mains supply via diode D1 would seem to indicate half wave rectification? If so, I can't quite understand why it is rectified prior to the transformer.

Thanks for the feedback.

Yes, at present I have disconnected all connectors (motor, pump etc.) from the circuit board.

Thanks for the feedback. How do I actually test the pump? Should I fill the washing machine with water before testing the pump and see if water exits the drain? Or is it possible to test the pump without fluid? Anyway, at present the pump is not connected to the circuit board.

If the triac fail shorted it could explain the excessive current drain?

The triac is connected to the circuit board via a large heatsink, so it seems difficult to remove (hence test for shorts). Any suggestions?

When I trace the 3pin connector going to the pump back to the circuit board, it seems that a relay (10A 125V AC, 12VDC) controls the pump.

Visual inspection of the circuit board indicates damage to resistor R1. Black soot is seen in the vicinity of diodes D1, D2, D3. The diodes does not seem damaged from visual inspection, although the wires of the diodes are not shiny, indicating current drain.

Sorry, it is actually TOP209P. At the top is written K021 and at bottom 1067 1B,

Thanks for all your kind help. Best regards, Theo

A picture is worth a thousand words... just remove the word "delete" from my email address.

Nor can I. The transformer would only produce the other half of the wave on the secondaries. This can't be right.

Test the pump wiring harness. Look for a short.

Assuming the pump to operate at mains voltage, just figure out which pins on the pump connector are for power, connect up a reasonable-guage power cord and plug it in. We're not trying to determine if this thing pumps water... at this point we don't really care. We just want to make sure that the windings aren't shorted and that the pump will start and run. It won't hurt it to run it dry.

That was my original thought, but I had some reservations, hence my questions about the existence of a relay which you have confirmed. The pump only operates at one speed, so can be controlled using a relay as opposed to a triac. The triac likely controls the motor so you can have slow-speed agitation and high-speed spin with no mechanical transmission. IF the triac controlled the pump and IF the triac were shorted, the pump would simply run all the time. This is not the case.

Confirm that the wash/spin motor works and that it's controlled by the large triac and move on.

Are diodes D1/D2/D3 and resistor R1 on the controlling 12VDC side of the relay or the load side?

If they're on the load side, and somehow I doubt they are, it's gotta be the pump or wiring. If they're on the control side, look for a smoked resistor (and perhaps diode) which limits current through the relay coil. If this failed it may take down any number of other components in the relay control circuit.

Well well well, that's a 3-terminal off-line PWM switch, as predicted. How many windings/leads on the transformer. The typical circuit diagram in the TOP209 datasheet shows it being used to derive a stable DC voltage via a transformer with a bias winding. It's possible that this guy produces the

Unfortunately Google only shows , not the complete email address (presumably to prevent spam). Can you send a message to my email address to which I can reply?

Thanks for all your feedback so far.

Best regards, Theo

How about getting a qualified engineer in to fix it before you kill yourself !

Advice to an amateur? not a chance mate, you might end up frying yourself.

Yes, lots of people kill themselves every year troubleshooting unpowered appliance circuits.

these types of equipment are far too complicated for the average individual to ever understand without a degree in engineering... turning a pump on and off on a timed cycle, whew! that's WAAAAYYYYY beyond me!

Best leave it to the "experts".

The OP obviously has some deductive skills and many times, that and some perseverance are all it takes to fix something. Thanks for your advice, but why don't you take your attitude and shove it where the sun don't shine?

Have a great day.

Dave

snipped-for-privacy@yahoo.delete.com

According to the connection diagram I sent previously, the mains is connected directly to diode D1 via a (blown, unknown value) resistor R1:

Furthermore, diode D1 is also connected to the transformer:

If C2 is indeed a polarised electrolytic capacitor (hopefully you'll be able to visually confirm from the JPEG I sent), it would seem to imply DC (direct current) - possibly half-wave rectification. Why a transformer is then connected to the diode D1 is, at present, unclear to me - I just don't understand it yet.

Thanks for the feedback. The electrician that helped us with the washing machine is unfortunately overseas at present, but the washing machine seemed to be working correctly (he started a program without any problems, then stopped the washing machine and pumped out all the water). However, when we started using the washing machine it would stop with a flashing light after 20 minutes. When I set the switch to leave the water in the washing machine, it carried on longer (up to about 1 hour 20 minutes) - but still did not complete the washing cycle. When I tried to pump out the water manually the problem with the shorted resistor occurred. The reason for the flasing light seemed to be related to the pumping out of water - I set the program to pump out water, but just heard a 'humming noise', which seems to indicate a problem with the pump. This would possibly explain why the machine stopped with a flashing light after 20 minutes - presumaby it tried (without success) to pump the water out for the next cycle to start.

At present I am not too worried about the pump, as I can always buy a cheap 'universal' pump to replace if needed. My big worry is about the electronics. At present I do not know the value of the damaged resistor (to replace) and whether additional components are damaged.

By the way, the electrician already made a modification with a switch that we now manually press to start the heating cycle (he also replaced the thermostat recently).

I have measured about 370R between the terminals of relay RL1 connected to the transformer windings (infinfity between other terminals):

So it would seem as though diodes D1/D2/D3 and resistor R1 is connecting to RL1 (via a transformer) on the controlling side. The other terminals of RL1 are connected to the connector on the circuit boad (presumably pump/motor) and the mains, so I assume it would be the switch controlled by the windings of RL1.

Is it possible to infer the likely value of resistor R1 from the text description of the connections? I would suspect that activating the relays could take a few hundred milli-amperes. A 2.5k resistor (damaged R1 resistor) would produce 240/2500 = 100mA, but in actual test got very hot in a few seconds - hence indicating a short somewhere?

I don't quite know how to draw a schematic diagram with text, but most connections to TOP209 have already been described:

I can add the following:

marked negative. Value is 22uF, 50V.

terminal of electrolytic capacitor C3 (16V 100uF).

The (small) transformer have 4 terminals.

Thanks for all your kind help. Best regards, Theo