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