I've been trying to trace a fault on my miele tumble dryer (T491, approx. 10 years old).
the problem is no heater comes on no matter the programme, timed or auto. So far I've checked the following:
1) Heater coils are perfect (no breaks)
2) Thermal switch has zero resistance so ok.
3) Temp sensor has room temp resistance 103k (its new)
4) The other temp sensor (NTC) in the fan housing at the front has room temp resistance 10k, dropping to about 3k in hot water.
5) Heater relay (K1) is working [tested out the machine] with a 9V battery. Switching voltage to it though in the machine is only 0.7V, as supplied from the EL423 so it doesn't activate.
6) On the EL423 i checked each of the 3 relays (again with 9v battery) and confirm they switch on/off while measuring the resistance on the output terminals. all seem to work.
7) Still on the EL423 i have measured the input voltages from the main controlling PCB (via solder tabs on EL423 with the 17 pin plug connected). using pin9 for ground.
- pin10 5.0v measures spot on
- pin11 30.0v measures at 31.1V
- pin13 K1 measures 5.99V matching the K1 relay 6V specs (i presume this is correct) This +6v DC passes correctly on the PCB to the tab for the K1 plug. Problem is when you measure voltage across both tabs only 0.7 volts is present so the relay never gets switched on.
From all this I guess that somehow the ground on the K1 tab isn't really ground, but more like +5.3v. net result being only 0.7V making it to the relay.
So my questions are:
- Do my findings above tell me all is OK with sensors, heaters etc?
- i see a 6.3A fuse mentioned in other posts related to no heating but cant seem to find one on my PCB - is there one?
Because the dryer works fine apart from the heating, could i safely repair it bypassing the PCB for the K1 relay? Solder a cable to the pin 13 (6v) and GND (pin 9) and send directly to the K1 heater relay?
long winded first post, but i'm desperate to fix it and avoid having to buy a new board (200 euros +) and/or a miele tech to visit (100 euros+)
any help/advice will be much appreciated.
cheers
Andy
the problem is no heater comes on no matter the programme, timed or auto. So far I've checked the following:
1) Heater coils are perfect (no breaks)
2) Thermal switch has zero resistance so ok.
3) Temp sensor has room temp resistance 103k (its new)
4) The other temp sensor (NTC) in the fan housing at the front has room temp resistance 10k, dropping to about 3k in hot water.
5) Heater relay (K1) is working [tested out the machine] with a 9V battery. Switching voltage to it though in the machine is only 0.7V, as supplied from the EL423 so it doesn't activate.
6) On the EL423 i checked each of the 3 relays (again with 9v battery) and confirm they switch on/off while measuring the resistance on the output terminals. all seem to work.
7) Still on the EL423 i have measured the input voltages from the main controlling PCB (via solder tabs on EL423 with the 17 pin plug connected). using pin9 for ground.
- pin10 5.0v measures spot on
- pin11 30.0v measures at 31.1V
- pin13 K1 measures 5.99V matching the K1 relay 6V specs (i presume this is correct) This +6v DC passes correctly on the PCB to the tab for the K1 plug. Problem is when you measure voltage across both tabs only 0.7 volts is present so the relay never gets switched on.
From all this I guess that somehow the ground on the K1 tab isn't really ground, but more like +5.3v. net result being only 0.7V making it to the relay.
So my questions are:
- Do my findings above tell me all is OK with sensors, heaters etc?
- i see a 6.3A fuse mentioned in other posts related to no heating but cant seem to find one on my PCB - is there one?
Because the dryer works fine apart from the heating, could i safely repair it bypassing the PCB for the K1 relay? Solder a cable to the pin 13 (6v) and GND (pin 9) and send directly to the K1 heater relay?
long winded first post, but i'm desperate to fix it and avoid having to buy a new board (200 euros +) and/or a miele tech to visit (100 euros+)
any help/advice will be much appreciated.
cheers
Andy
