Help diagnosing a coffee maker PCB

[oneplustwo]

Hi there,

I have an 15 year old coffee maker (KitchenAid Proline KPCM050PM0.)

It intermittently works but seems to have now bit the bullet. I believe the relay is bad as it seems to try to turn on as indicated by the LED when I turn the momentary rotary knob but I don't hear the relay latch and then the light goes off. (Normal behavior is the light goes on, I hear the relay switch, and then everything proceeds as you would expect.)

Here are some photos of the PCB. The PCB is obsolete or I would just replace the whole thing. Instead, I'm looking to replace the most likely faulty part and go from there. Any other advice to trouble shoot? The relay doesn't seem to be readily available either but someone is selling lots of 10 on ebay. I've asked if they'll just sell me one or two.

Thanks!

 

[sagor1]

It could be one of several things. First, I'd check the transformer, input voltage and output voltage. Some of those transformers have a thermal fuse under the "blue tape" winding on the primary side. Those sometimes fail and you get no secondary voltage.
Then, check the DC voltage around the regulator (probably the TO-220 transistor looking device), hard to tell from the photos. There should be a 5VDC voltage somewhere around there.
That voltage is then switched "somewhere" to turn on the relay. If you have an external 5V supply, try to test the relay directly and check its contacts to see if they operate. It is possible the contacts are burned out. It is also possible the device driving the relay is blown, but that could be off-board somewhere else.

Good luck

 

[ramondo]

Not an expert!! I would check the two capacitors that are tilted slightly (unless you moved them yourself) because they do not always bulge on the top. I believe caps are like batteries,,(they will go bad), other parts are like windshields (not likely to go bad but can be broken).

 

[oneplustwo]

It does look like there is a thermal fuse on the xformer so that could be the issue. And the TO-220 transistor thing is indeed a 7805CT 5VDC regulator.

I like the analogy of the batteries and windshields though. Caps are easy to find replacements for as well.

I also noticed the back side of the PCB has some SMD components (and the quality of the soldering isn't great.). One of the pins came loose when I removed one of the spade connectors for example. So I may reflow some of the joints if I'm going to remove the caps.

Or... I may just buy a new coffee maker. I really like this one though. It's built like a tank... except for the PCB.

 

[rjenkinsgb]

The relay seems fairly easy to get, if you do need one - eg. this is the same make:

Relay coil 5VDC, contact 120VAC/15A 1x switching RAS-05-15 | GM electronic COM

www.gmelectronic.com

Or this seems to be an exact Omron replacement from Digikey:

G5LE-1-E DC5 Omron Electronics Inc-EMC Div | Relays | DigiKey

Order today, ships today. G5LE-1-E DC5 – General Purpose Relay SPDT (1 Form C) 5VDC Coil Through Hole from Omron Electronics Inc-EMC Div. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.co.uk

Do replace the electrolytics; they may not all need doing, but it's cheap an eliminates a very common problem.

 

[Diver300]

As far as I can tell from the specifications of the coffee maker, the heater is rated at 1350 W, so that it taking around 12 A. That is within the rating of the relay, but not by a lot. The relay is rated up to 85 % humidity, so it probably isn't a sealed relay, and it's on a coffee maker that works by generating steam.

It wouldn't surprise me at all if the relay contacts have degraded.

 

[sagor1]

If it is the thermal fuse, they can be replaced, though difficult at times. Part numbers are usually written on them. They are usually low values, like 1A or 2A. I had one generator battery charger that had this issue but I simply bridged the broken fuse with an external fuse. There was no thermal failure (no heated areas), just "aging" that caused the failure or a faulty component. Since the unit is outside, I have no worries about any overheating of the transformer, if it gets too hot, it is drawing too much current and the external fuse will blow.

 

[oneplustwo]

Thanks for all the input. That Omron direct replacement is a good fine. Any chance there's a direct drop in that is higher rated? There's probably an easy way to figure that out that I'm ignorant of?

 

[rjenkinsgb]

Any chance there's a direct drop in that is higher rated?

These appear to be compatible, 20A rated but "Form A" contact rather than "Form C" - in other words, a normally open contact rather than a changeover contact. If the normally closed one is not used in the machine, it could work.
(The changeover one in the same series is rated 17A, presumably as there is less space for contact material when three contacts are required.

HF152FD/5-1HTF(335) | Hongfa Europe GMBH PCB Mount Power Relay, 5V dc Coil, 20A Switching Current, SPNO | RS Components

uk.rs-online.com

 

[oneplustwo]

I might as well just stick to the old one to make sure it works. It lasted for 15 years so I figure it can't be that terribly underrated. I also dug into the old parts bin from when I was doing a lot of DIY audio stuff and found some Nichicon gold caps that should be fine replacements although not exactly direct drop-ins. This is going to be the best sounding coffee machine ever! =)

Unfortunately, I couldn't find any 10uF 50V ones amongst the spare parts bin. Closest I have is 100uF which might be fine although I might as well just buy some new ones if I'm going to order the relay anyway. Parts cost will be less than shipping but oh well. Such is the price of DIY.

 

[rjenkinsgb]

I just realised from looking at the PCB underside, that the original relay is a Form A type - only four pins.

The 20A should be fine in that case, or of you use a five pin type (Form C) you will have to cut off the redundant pin, as there is no provision for it in the PCB.

 

[oneplustwo]

Ah, good catch. I already ordered the parts though but thanks for educating me on that! Shipping was more than the parts! Too bad amazon doesn't have a great selection of these things.

 

[Nigel Goodwin]

Ah, good catch. I already ordered the parts though but thanks for educating me on that! Shipping was more than the parts! Too bad amazon doesn't have a great selection of these things.

Amazon isn't the place you buy components, but there are plenty of specific component suppliers out there - all over the world.

 

[oneplustwo]

Yup. I prefer Mouser typically. Parts arrive Thursday so hopefully I'll be good to go after a few solder joints. Will report back.

 

[oneplustwo]

Well, good news is the parts arrived and I got them installed without issue. Although the relay did have that extra pin that @rkenkinsgb mentioned for the Form C relay.

Bad news is that I get the same behavior. I should have ordered the 5V voltage regulator and replaced that at the same time. The other area mentioned was the thermal fuse at the transformer. Is there a way to test that? Any other ideas for next steps?

 

[Nigel Goodwin]

Well, good news is the parts arrived and I got them installed without issue. Although the relay did have that extra pin that @rkenkinsgb mentioned for the Form C relay.

Bad news is that I get the same behavior. I should have ordered the 5V voltage regulator and replaced that at the same time. The other area mentioned was the thermal fuse at the transformer. Is there a way to test that? Any other ideas for next steps?

A thermal fuse can simply be tested by reading it with a multimeter set to ohms - it should be near zero ohms - it's just a type of fuse.

 

[augustinetez]

I'd more inclined to look for faulty joints rather than just using the shotgun approach of replacing bits.

Looking at the bottom side photo in Post #4, I can see at least 4 candidates that could be causing problems:

Set of three joints next to the R35/C15 combo

Right hand joint above R30.

I would also check where every connector is mounted on the pcb.

And that's even assuming the fault is on this board.

 

[ramondo]

Is the rotary knob a switch AND a rheostat? Switch ok but resistor might be open? Also open or shorted heating unit may be at fault,, have you ruled these out?

 

[oneplustwo]

Thanks for the ideas. I believe the rotary knob is just a momentary switch. I haven't taken that section apart so perhaps one more thing to delve into. I had not thought about the heating unit being at fault. Assuming I can identify those wires, what should I expect it to read? Just not zero or open?