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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Voltage converter circuit - Bosch / Siemens washing machine
I need your help repairing the voltage conversion circuit of the Bosch
WFL2061BY washing machine. I have the following questions: 1) No operating lights etc. are on. Visual inspection shows a damaged resistor (first two bands brown and black, next band difficult to tell - possibly brown, gold or even yellow). As far as I can tell no fuse is fitted - is this normal? A fuse seems to be essential to protect against possible overcurrent conditions. 2) The damaged resistor is directly connected to the mains in series with a transformer (which I suspect is used to derive the low voltage for driving the relays). I have experimented with a 100R resistor (1/4 Watt) connected to 220V, but it is immediately burned out. Four (1/4 Watt) resistors of 10k in parallel also got hot in a few seconds. My initial guess would be that the damaged resistor provides current limiting? 3) If the damaged resistor provides current limiting, why is it placed on the high voltage (220V) side? 4) A number of diodes (likely 1N4001) also seems to be connected to the high voltage side, before the transformer. If they form a half- wave or full-wave rectifier, why do they connect the diodes before the transformer (on the high voltage side)? 5) It is possible that some other components also got damaged. From visual inspection I cannot confirm damage to other components. In circuit measurements of the diodes show about 4.5k in one direction and infinity in the other. An 8 pin IC TP209P is found close to the (small) transformer. The voltage regulator is a BT916 (or BTB16 - difficult to tell from visual inspection). Any suggestions on how to proceed? Best regards, Theo van der Merwe |
#2
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Voltage converter circuit - Bosch / Siemens washing machine
wrote in message ups.com... I need your help repairing the voltage conversion circuit of the Bosch WFL2061BY washing machine. I have the following questions: 1) No operating lights etc. are on. Visual inspection shows a damaged resistor (first two bands brown and black, next band difficult to tell - possibly brown, gold or even yellow). As far as I can tell no fuse is fitted - is this normal? A fuse seems to be essential to protect against possible overcurrent conditions. 2) The damaged resistor is directly connected to the mains in series with a transformer (which I suspect is used to derive the low voltage for driving the relays). I have experimented with a 100R resistor (1/4 Watt) connected to 220V, but it is immediately burned out. Four (1/4 Watt) resistors of 10k in parallel also got hot in a few seconds. My initial guess would be that the damaged resistor provides current limiting? 3) If the damaged resistor provides current limiting, why is it placed on the high voltage (220V) side? 4) A number of diodes (likely 1N4001) also seems to be connected to the high voltage side, before the transformer. If they form a half- wave or full-wave rectifier, why do they connect the diodes before the transformer (on the high voltage side)? 5) It is possible that some other components also got damaged. From visual inspection I cannot confirm damage to other components. In circuit measurements of the diodes show about 4.5k in one direction and infinity in the other. An 8 pin IC TP209P is found close to the (small) transformer. The voltage regulator is a BT916 (or BTB16 - difficult to tell from visual inspection). Any suggestions on how to proceed? Best regards, Theo van der Merwe There's certainly a shorted component which burned up the resistor. Resistors don't just burn up on their own. |
#3
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Voltage converter circuit - Bosch / Siemens washing machine
On Jun 4, 8:21 pm, "James Sweet" wrote:
wrote in message ups.com... I need your help repairing the voltage conversion circuit of the Bosch WFL2061BY washing machine. I have the following questions: 1) No operating lights etc. are on. Visual inspection shows a damaged resistor (first two bands brown and black, next band difficult to tell - possibly brown, gold or even yellow). As far as I can tell no fuse is fitted - is this normal? A fuse seems to be essential to protect against possible overcurrent conditions. 2) The damaged resistor is directly connected to the mains in series with a transformer (which I suspect is used to derive the low voltage for driving the relays). I have experimented with a 100R resistor (1/4 Watt) connected to 220V, but it is immediately burned out. Four (1/4 Watt) resistors of 10k in parallel also got hot in a few seconds. My initial guess would be that the damaged resistor provides current limiting? 3) If the damaged resistor provides current limiting, why is it placed on the high voltage (220V) side? 4) A number of diodes (likely 1N4001) also seems to be connected to the high voltage side, before the transformer. If they form a half- wave or full-wave rectifier, why do they connect the diodes before the transformer (on the high voltage side)? 5) It is possible that some other components also got damaged. From visual inspection I cannot confirm damage to other components. In circuit measurements of the diodes show about 4.5k in one direction and infinity in the other. An 8 pin IC TP209P is found close to the (small) transformer. The voltage regulator is a BT916 (or BTB16 - difficult to tell from visual inspection). Any suggestions on how to proceed? Best regards, Theo van der Merwe 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 |
#4
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Voltage converter circuit - Bosch / Siemens washing machine
wrote in message oups.com... On Jun 4, 8:21 pm, "James Sweet" wrote: wrote in message ups.com... I need your help repairing the voltage conversion circuit of the Bosch WFL2061BY washing machine. I have the following questions: 1) No operating lights etc. are on. Visual inspection shows a damaged resistor (first two bands brown and black, next band difficult to tell - possibly brown, gold or even yellow). As far as I can tell no fuse is fitted - is this normal? A fuse seems to be essential to protect against possible overcurrent conditions. 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. 2) The damaged resistor is directly connected to the mains in series with a transformer (which I suspect is used to derive the low voltage for driving the relays). I have experimented with a 100R resistor (1/4 Watt) connected to 220V, but it is immediately burned out. Four (1/4 Watt) resistors of 10k in parallel also got hot in a few seconds. My initial guess would be that the damaged resistor provides current limiting? Something's shorted and drawing too much current. A metal film resistor tends to be a pretty good fuse in many cases. 3) If the damaged resistor provides current limiting, why is it placed on the high voltage (220V) side? Less current, smaller resistor, cheaper. Also, it ensures that the transformer is not hot in the event of a fault. 4) A number of diodes (likely 1N4001) also seems to be connected to the high voltage side, before the transformer. If they form a half- wave or full-wave rectifier, why do they connect the diodes before the transformer (on the high voltage side)? 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). 5) It is possible that some other components also got damaged. From visual inspection I cannot confirm damage to other components. In circuit measurements of the diodes show about 4.5k in one direction and infinity in the other. An 8 pin IC TP209P is found close to the (small) transformer. The voltage regulator is a BT916 (or BTB16 - difficult to tell from visual inspection). Any suggestions on how to proceed? 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 15VDC out, 50mA rating... Dave Best regards, Theo van der Merwe 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 |
#5
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Voltage converter circuit - Bosch / Siemens washing machine
On Jun 5, 8:43 pm, "Dave" wrote:
wrote in message oups.com... On Jun 4, 8:21 pm, "James Sweet" wrote: wrote in message roups.com... I need your help repairing the voltage conversion circuit of the Bosch WFL2061BY washing machine. I have the following questions: 1) No operating lights etc. are on. Visual inspection shows a damaged resistor (first two bands brown and black, next band difficult to tell - possibly brown, gold or even yellow). As far as I can tell no fuse is fitted - is this normal? A fuse seems to be essential to protect against possible overcurrent conditions. 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. Thanks for the feedback, now I understand better. 2) The damaged resistor is directly connected to the mains in series with a transformer (which I suspect is used to derive the low voltage for driving the relays). I have experimented with a 100R resistor (1/4 Watt) connected to 220V, but it is immediately burned out. Four (1/4 Watt) resistors of 10k in parallel also got hot in a few seconds. My initial guess would be that the damaged resistor provides current limiting? Something's shorted and drawing too much current. A metal film resistor tends to be a pretty good fuse in many cases. 3) If the damaged resistor provides current limiting, why is it placed on the high voltage (220V) side? Less current, smaller resistor, cheaper. Also, it ensures that the transformer is not hot in the event of a fault. Thanks for the feedback, now I understand better. 4) A number of diodes (likely 1N4001) also seems to be connected to the high voltage side, before the transformer. If they form a half- wave or full-wave rectifier, why do they connect the diodes before the transformer (on the high voltage side)? 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). I can send you a JPEG of the circuit board if it can help, but below is a brief description of the connections: From mains to multipole switch (selecting program) to resistor R1 (the damaged resistor of unknown value, probably 2W from the size) From mains to multipole switch (selecting program) to capacitor C1 (and R1). C1 is a large 0.22uF 275V AC From mains to multipole switch (selecting program) to resistor R2 (Red 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). From mains to multipole switch (selecting program) to connector (could be pump/motor). From resistor R1 (other end) to diode D1 (Anode) From diode D1 (Cathode) to D2 (Cathode) From diode D1 (Cathode) to C2 (large 400V 10uF). The other end of C2 is marked -, so it could be polarised capacitor (looks like an electrolytic capacitor). From diode D1 to transformer terminal 1 From mains live (other connection) to multipole switch to capacitor C1 (other end) From mains live (other connection) to relay From mains live (other connection) to blue component with 2 connections marked S10 K275 0013 From mains live (other connection) to transformer terminal 2 From mains live (other connection) to pins 1,2,3,7,8 of IC 1 (TOP92P) From mains live (other connection) to pin 1 of IC2 (BTB16T) From mains live (other connection) to many other components (e.g. small components looking like surface mount capacitors) From transformer terminal 3 to diode D3 (Cathode) From transformer terminal 3 to pin 5 IC1 (TOP92P) From transformer terminal 4 to diode D4 (Anode) From diode D4 (Cathode) to capacitor C3 with thick trace (presumably positive, other end marked - . Looks like electrolytic capacitor 16V 100uF). From diode D4 (Cathode) to small diode D5 (Anode). D5 looks like 1N4148?? From diode D4 (Cathode) to Relay R1 (on the circuit board a plus sign is found next to the connection to the relay). From relay R1 to connector (motor/pump?) 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. 5) It is possible that some other components also got damaged. From visual inspection I cannot confirm damage to other components. In circuit measurements of the diodes show about 4.5k in one direction and infinity in the other. An 8 pin IC TP209P is found close to the (small) transformer. The voltage regulator is a BT916 (or BTB16 - difficult to tell from visual inspection). Any suggestions on how to proceed? 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. Thanks for the feedback. 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. Yes, at present I have disconnected all connectors (motor, pump etc.) from the circuit board. 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. 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 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 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? 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? 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. 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 15VDC out, 50mA rating... 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 Dave Best regards, Theo van der Merwe 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 |
#6
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Voltage converter circuit - Bosch / Siemens washing machine
wrote in message ups.com... I can send you a JPEG of the circuit board if it can help, but below is a brief description of the connections: A picture is worth a thousand words... just remove the word "delete" from my email address. If so, I can't quite understand why it is rectified prior to the transformer. Nor can I. The transformer would only produce the other half of the wave on the secondaries. This can't be right. 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. 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. If the triac fail shorted it could explain the excessive current drain? 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. The triac is connected to the circuit board via a large heatsink, so it seems difficult to remove (hence test for shorts). Any suggestions? Confirm that the wash/spin motor works and that it's controlled by the large triac and move on. 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? 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. 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. Sorry, it is actually TOP209P. At the top is written K021 and at bottom 1067 1B, 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 12VDC to operate the relay. A schematic would be really helpful here. Thanks for all your kind help. Best regards, Theo Dave Best regards, Theo van der Merwe 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 |
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