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Old 10-14-2019, 07:40 AM   #1
notallbad
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Default Tumble dryer 'Smart lamp' pcb

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.
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Last edited by notallbad; 10-14-2019 at 07:45 AM..
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Old 10-14-2019, 12:12 PM   #2
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Default Re: Tumble dryer 'Smart lamp' pcb

cracked solder joints on atleast one connector there
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Old 10-15-2019, 06:24 AM   #3
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Default Re: Tumble dryer 'Smart lamp' pcb

Reflowed joints but fault still persists.
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Old 10-15-2019, 02:00 PM   #4
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
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?

Last edited by R_J; 10-15-2019 at 02:04 PM..
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Old 10-15-2019, 02:10 PM   #5
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Default Re: Tumble dryer 'Smart lamp' pcb

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.
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Old 10-16-2019, 06:05 AM   #6
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by R_J View Post
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
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Last edited by notallbad; 10-16-2019 at 06:07 AM..
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Old 10-16-2019, 06:15 AM   #7
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by redwire View Post
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!
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Old 10-16-2019, 08:18 AM   #8
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by redwire View Post
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.

Last edited by notallbad; 10-16-2019 at 08:20 AM..
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Old 10-16-2019, 10:55 AM   #9
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Default Re: Tumble dryer 'Smart lamp' pcb

Can you read the number on U1 ? you may need to clean the top with alcohol to read the number.
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Old 10-16-2019, 11:17 AM   #10
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Default Re: Tumble dryer 'Smart lamp' pcb

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.
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Old 10-16-2019, 07:23 PM   #11
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by r_j View Post
can you read the number on u1 ? You may need to clean the top with alcohol to read the number.
u1 - mb95f582k
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Old 10-16-2019, 07:38 PM   #12
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Default Re: Tumble dryer 'Smart lamp' pcb

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.

Last edited by notallbad; 10-16-2019 at 07:47 PM..
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Old 10-16-2019, 09:40 PM   #13
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by notallbad View Post
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)

Last edited by R_J; 10-16-2019 at 09:46 PM..
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Old 10-17-2019, 02:07 AM   #14
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by R_J View Post
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
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Old 10-17-2019, 06:31 AM   #15
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Default Re: Tumble dryer 'Smart lamp' pcb

Quote:
Originally Posted by redwire View Post
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.

Last edited by notallbad; 10-17-2019 at 06:33 AM..
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Old 10-17-2019, 07:52 AM   #16
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Default Re: Tumble dryer 'Smart lamp' pcb

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'!
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Old 10-17-2019, 11:02 AM   #17
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Default Re: Tumble dryer 'Smart lamp' pcb

Where the heck is C4?
https://www.badcaps.net/forum/attach...1&d=1571056408
https://www.badcaps.net/forum/attach...2&d=1571056408
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Old 10-17-2019, 11:07 AM   #18
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Default Re: Tumble dryer 'Smart lamp' pcb

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.
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Old 10-17-2019, 11:21 AM   #19
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Default Re: Tumble dryer 'Smart lamp' pcb

It is kind of bad to have the replacement board with bad cap already.
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Old 10-17-2019, 01:59 PM   #20
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Default Re: Tumble dryer 'Smart lamp' pcb

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.
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