Blomberg electric dryer - Need a replacement relay

[steves7839]

A neighbors Blomberg electric dryer has been tumbling OK but refused to heat. The heater coil and sensors test OK.
The control board relays are pictured. Only one of the four cannot be activated with current to the relay coil terminals from a 9V battery.

What brand/manufacturer is this relay? I've tried searching the numbers on the Digikey website to no avail.

[redwire]

It's a cube relay rated resistive load 10A 125/277VAC, 12VDC coil.
Panasonic JS1a-B-12V-FT but obsolete now.
Consider Omron G5LE-1A-DC12 or the high capacity or sealed versions would work as well. Note there is a safety spec on the original relay for "Flame resistance and tracking resistance meet EN60335-1" as the "T" option that I don't specifically see for the Omron.

[steves7839]

Originally Posted by redwire

Consider Omron G5LE-1A-DC12.

Looks the same. I just ordered three from Digikey. Thanks!

[steves7839]

I replaced both relays that power the heater coils. Perfect fit. To my surprise nothing changed on the control board. The R5 relay would not switch when activating the coil terminals with 9Vdc through a resistor. I also found (or melted) and replaced the diode that shorted when I tried to activate the R5 coil.

Tomorrow, I plan to test the reworked control board in the dryer but am not optimistic.

Does anyone know of a schematic for a Blomberg control board?

[DennisH]

October 18, 2022 - The OEM relay (or a clone of it) appears to be for sale on eBay right now in case you're interested.

To see it, go to eBay.com and put "134100464686" in the search box (without the quotes) - then click Search.

[stj]

10A @120v is only about 1.2KW
is the relay overloaded or does the dryer have a crap heater?

in europe our dryers are 2KW+, at 120v that would be 16A

[steves7839]

Thank you for that ID!
The heater coils are rated 600W and 1400W and can be run separately or simultaneously, thus separate relays. To my surprise, the stuck relay powers the lower-wattage coil.

[eccerr0r]

USA dryers are also 2KW+, but usually run across both phases for 240V so we don't have 16A circuits...

[petehall347]

did you test it in circuit ? if so the flyback diode might be shorted or you connected battery wrong way .

[redwire]

Blomberg don't seem to offer any service manuals, I kinda regret buying their dishwasher now

Appliance control board relays fail mostly due to contact arcing - manufacturers refuse to add a RC snubber or MOV to mitigate this and give longer life. Load current doesn't matter much - any heater, motor, solenoid etc. can generate contact arcing. The relays can also fail due to contact heat as the contacts wear- they can melt their housing.
There have been many appliance board fires/recalls due to cracked/bad solder joints on the PC boards as well, always do a visual and touch ups with the soldering iron.

The JS 12V coil pull-in minimum is around 8.4V/30mA so a 9V battery should do it, unless the surrounding circuitry is in the way or polarity is wrong. A "click" doesn't always say much, as far as bad contacts. The real test is to pull a relay off the board and use a bench power supply to move the coil, as well as pass good current through the contacts like a car tail light bulb load. An ohmmeter reading is no good across closed-contacts due to oxides, carbon etc. giving what look like good readings that fizzle out under load. You have to run at least an 0.5-1amp through the contacts to test them.

Another option is Songle SRD-12VDC-SL-C cheap and easy to find, or Song Chuan 215H-1AH-F-C-12VDC {Mouser}. Although the Japanese brands are best quality, only Omron seems to still be making these size sugar cube relays.

[redwire]

I guess no Blomberg appliance service manuals exist on the Internet
If you provide clear pictures of the board (both sides) we can figure out a few things.
There can be a safety-interlock, such as a door switch, fan airflow, overtemp etc. that could be in the way preventing the heater relay from engaging in the first place. A few (front loading) appliances have kooky door locks as well, using a PTC heater/latch, because children apparently climb in there for a wash or dry.

[steves7839]

I ordered a replacement control board. My primary concern is whether the moisture sensor could be open. It consists of two metal plates fixed inside the drum. Naturally it ohms in megohms from the control board connection. But the transformer that “senses” changes in moisture level also reads very high ohms. I suspected a dry reading might cause the heater to disable. So I added wet laundry but it made no difference.

Any technique for testing or bypassing that moisture sense circuit?

[sam_sam_sam]

Originally Posted by redwire

because children apparently climb in there for a wash or dry.

They are not supposed to do things like that

[redwire]

We don't have a model number, no pictures- you're making this too difficult to help.
The "humidity sensor" is two metal electrodes that conductivity is monitored. If moist clothes touch the sensors, it registers a blip as "still wet".
The electrodes can get a buildup of fabric softener wax or mineral deposits on them which would give high resistance (=dry clothes). Even if the humidity sensor wrongly reads dry, it should run for minimum of a couple minutes before shutting off.
You could spoof wet clothes with maybe a 1MEG resistor or wet noodle across the electrodes. I don't know what "transformer" you are talking about, they don't use that for a moisture sensor.

[steves7839]

Originally Posted by redwire

We don't have a model number, no pictures- you're making this too difficult to help.

Not intentionally, but here is the fix. Model is Blomberg DV16540. I'm posting pics of the schematic included with the dryer, and the main board. Very little detail of the main board circuitry was provided.
The connection to the moisture sensor plates is at the upper right of the main board, labelled KN5 on the schematic but screen printed KN1 on the main board.

[stj]

check the drive transistor for the relay coil

[redwire]

RLY5 driver transistor Q32 would be the same type as Q31. I can't see if the Q32 base leading from R109 goes to Q31 or anything (some safety interlocks etc) other than right to the MCU, pic is too blurry to follow the relay power as well.
For functional safety, there can be a master power switch (transistor) for the heater relay coil power, as well as the individual on/off transistor for each heater.

Back-EMF diode D26 is missing, MELF package like LL4148 or LL/DL4002 etc. It would get blown if the 9V battery was connected backwards I think. You still need a diode there.
A q-tip and IPA can clean off the extra flux.

[steves7839]

Originally Posted by redwire

RLY5 driver transistor Q32 would be the same type as Q31.
For functional safety, there can be a master power switch (transistor) for the heater relay coil power, as well as the individual on/off transistor for each heater.

Q32 and Q31 do not appear to be interconnected. With a multimeter in ohms and diode check modes they appear to be normal and resemble the drivers of the motor relay coils.

Originally Posted by redwire

Back-EMF diode D26 is missing, MELF package like LL4148 or LL/DL4002 etc. It would get blown if the 9V battery was connected backwards I think. You still need a diode there.

I installed a larger diode for D26, a 1N4004, after this pic was taken. Yes, I must have forward biased D26, since the solder melted.

[ajshoe]

your swaping parts without testing. first thing I would do is monitor voltage out of heat relays. turn on dryer with heat. If your getting voltage (110V for each relay - has 2 elements so the control bd controls the amount of heat in the drum) - problem is down the line - sensors, wiring, heater. if not - next take out relays and bench test them. If relays all test good and no voltage -- test caps on control board for proper ESR. not a good idea testing relays in circuit board. I repair these boards occasionally - unfortunately some dryer boards have a proprietary chip on them that sometimes is the cause of failure (whirlpool is famous for this). doesn't look like this one does. worked on a lot of dryers but never seen a blomberg !

[redwire]

If the heater relay transistors are independent, then it's either the switch circuit for the relay coil or the MCU is refusing to turn on high heat.
Have you checked the heater temp sensor? 19.5kΩ at 25°C. To see if the board thinks the heater temperature doesn't warrant high heat on.
(same as the door NTC apparently but I think it gets heated to lock).