Tumble dryer 'Smart lamp' pcb

[notallbad]

This operates the drum lamp on a tumble dryer when the door is opened.
The lamp does come on but is strobing at a constant rate.

The triac is Z3M and the uc is a MB95F582K.

Is it likely the uc is stuck in reset?

Resistors, diodes and cap C1 all appear ok.

KN1 connections as follows:
N.C
RST
DBG
Vcc
Gnd

Any ideas please.

[stj]

cracked solder joints on atleast one connector there

[notallbad]

Reflowed joints but fault still persists.

[R_J]

Resistors, diodes and cap C1 all appear ok.

How did you check the cap? What connects to KN1? does it connect to the main controller board of the dryer? or just the door switch?

[redwire]

I would also check the large square blue film cap, part of a capacitive dropper for MCU power. Careful it has no discharge resistor, so first use a multimeter to read volts and ensure it has no stray charge.
Resolder connector pins KN3, KN2 and somebody is resoldering but not using enough heat, in the pics. Just need to keep the iron there for a second or two longer.

The MCU seems to turn on the triac TR1 for an incandescent 15W lamp. Why does it use an MCU to turn on a light bulb?

I would expect 5V at zener D5 or Z1 as MCU power.

[notallbad]

Originally Posted by R_J

How did you check the cap? What connects to KN1? does it connect to the main controller board of the dryer? or just the door switch?

Replaced cap C1.

KN1 not connected to anything.

KN3 - Lamp
KN2 - Door switch 'Live', live and neutral

My diagram was wrong - had 'N' and 'L' reversed

[stj]

Originally Posted by redwire

Why does it use an MCU to turn on a light bulb?

you dont understand marketing, if you dont put a chip somewhere you cant write "smart" in the name / product description!

[notallbad]

Originally Posted by redwire

I would expect 5V at zener D5 or Z1 as MCU power.

Across C1 neg and D5 reading 0.9v
and
acrosd C1 neg and Z1 reading 2.6v

These readings are the same on both boards, I have 2 of them, both faulty with the same symptoms i.e flashing/strobing.

[R_J]

Can you read the number on U1 ? you may need to clean the top with alcohol to read the number.

[budm]

Both boards are doing the same thing, mmm.
The lamp is just a incandescent lamp?
What happen if you bypass the TRIAC?
Door switch contacts are good and not intermittent?
I wonder if the door switch can handle 15W load since the dryer does not need this stupid smart lamp function so the board can be bypassed.
You can bypass the board and use the door switch to light up LED bulb instead too.

[notallbad]

Originally Posted by r_j

can you read the number on u1 ? You may need to clean the top with alcohol to read the number.

u1 - mb95f582k

[notallbad]

I think the problem lies with never or rarely being maintained, as with all the machines I acquire first port of call is giving them a thorough clean inside and out.

I always recommend that after EVERY use that the water tray is emptied, the fluff filter cleaned, filter housing and door seal and inner door face wiped and EVERY 3 months that the condenser is flushed through with water / wiped over and its housing cleaned.
Following these simple guidelines which never really takes long to do can prolong the life of the machine as well as continuing its efficient operation.

To be honest the problem here I believe is due to the lamp cover inside the drum cracking and breaking away which then leads to humidity reaching the Smart lamp board which has no other means of protection other than a plastic housing and of course can also damage the main control board which leads to other problems.

[R_J]

Originally Posted by notallbad

u1 - mb95f582k

The ic needs +5 volts on it's VCC pin to operate. There is a small chip cap, C3 check the voltage across it, it goes between pin3 (ground) and pin6 (VCC)

[notallbad]

Originally Posted by R_J

The ic needs +5 volts on it's VCC pin to operate. There is a small chip cap, C3 check the voltage across it, it goes between pin3 (ground) and pin6 (VCC)

U1 - pin 3 to pin 6 - 2.6v

[notallbad]

Originally Posted by redwire

I would also check the large square blue film cap, part of a capacitive dropper for MCU power. Careful it has no discharge resistor, so first use a multimeter to read volts and ensure it has no stray charge.
Resolder connector pins KN3, KN2 and somebody is resoldering but not using enough heat, in the pics. Just need to keep the iron there for a second or two longer.

The MCU seems to turn on the triac TR1 for an incandescent 15W lamp. Why does it use an MCU to turn on a light bulb?

I would expect 5V at zener D5 or Z1 as MCU power.

Thanks, swapped out C4 - 100nf cap on both boards and all working again!

Thanks very much.

[notallbad]

Well actually, it was a 150nf X2 cap but I only have 100nf but working again.

There is a timer function that switches the lamp off after 2 1/2 minutes or 15 secs after the door is closed, now isn't that 'Smart'!

[budm]

Where the heck is C4?
https://www.badcaps.net/forum/attach...1&d=1571056408
https://www.badcaps.net/forum/attach...2&d=1571056408

[R_J]

Good to here its working, C4 is used to isolate and couple the a/c to the D1/D2 diodes, C1 is the filter and Z1 should be the regulator for 5 volts that supplies the voltage for the ic, I suspect the voltage across pins 3 & 6 is closer to 5v now.

[budm]

It is kind of bad to have the replacement board with bad cap already.

[redwire]

Glad it's working, these appliance boards can be priced crazy high.
Can you post the dryer model number or board p/n for others who might end up here.

I see more and more film capacitors failing in capacitive dropper use. It seems to be the metalization is cracking and flaking inside. Epcos parts are not lasting.