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Keurig B60 slow flow problem & repair experience

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Keurig B60 slow flow problem & repair experience

Postby dweeezil » Sat Apr 20, 2013 8:32 pm

Hello,

I've got a several year old B60 that developed the dreaded "dribbly slow flow" problem. I don't have it repaired yet, but I think I'm on to the problem. I learned so much from the "B70 thread" on this site that I wanted to share a few things I've not seen mentioned before and also to ask if anybody has an idea what might be the problem with my machine.

As a bit of background, I had a very old B60 (single solenoid and the 120VAC pump) available to practice disassembly on and to use for parts. One of the things I learned rather quickly while disassembling my newer machine is how different it is from the older one. From my readings in this forum, I can see there are at least 3 different generations of B60 machines: The old ones have a 120VAC motor, a single solenoid and rather simple plumbing. Somewhat newer ones have 2 solenoids, a much quieter 12VDC pump (with a tube connected to its suctions side) and very complex plumbing overall. From the pictures I've seen on this board, there's a newer generation (the newest?) that I've never seen in person that has dual overflow tubes and much simpler routing of the aft solenoid's lower tube.

One thing that took me a bit to realize after reading the B70 thread is that the functions of the forward and aft solenoids are reversed between the B70 and the B60. The internal layout of the B60 seems much nicer in that the aft solenoid is the one that will leak and there's nothing major underneath it that will get damage when it does leak. The air pump is in an enclosed area and seems well protected. I'd be surprised to see a water damaged air pump in a B60.

The first obvious problem my machine had was, of course, the leaky aft solenoid. I understood that wasn't the cause of my slow flow problem. After removing and examining the solenoid, I figured it had been jammed up for a long time (years?) but wasn't really causing any problems. I got a couple of clean-looking replacements anyway (at sciplus.com's local store) and installed one of them.

At first, I figured the cause of my slow flow must have been a weak air pump. I swapped in the pump from my parts machine and it seemed to flow even a bit slower. After disassembling both air pumps and not finding anything wrong with them, I re-installed the original one. Strangely enough, the machine started working much better. My wife and I used it for a few days (I left the shroud off it) and, sure enough, it eventually slowed down.

Further reading and experimentation made me realize that the air pump is not driven at a constant speed or with constant torque. During my years of use, I didn't realize what I was hearing inside the machine but now I know that the air pump speeds up during the end of the brew cycle in order to force air through the K cup. Furthermore, it seems the system varies the power to the air pump to provide a constant brewing rate regardless of the amount of coffee in the K cup or the resistance it provides. I figured there was a clog in the air line to the pressure sensor or that the sensor was defective. I removed the upper board and gently cleaned the inlet of the pressure sensor and blew out the hose and after reassembling it, the machine worked great. I figured it had been fixed.

After another day or so, it slowed down again almost to the point of stopping.

After thinking about my repair, try, re-repair, try cycle, it dawned on me that the machine was working well when it had cooled down a bit and work more poorly the longer it remained powered on. For the record, we have always left the machine turned on 24/7 because we make coffee at all times of the day. I'll also note that the internals of the machine were almost totally scale-free. I've been using RO water for years and still de-scale regularly.

That brings me to the present: My current theory is that there's a faulty component on the power board. I've got it running now with the cover to the power board removed and have run a few cups of water through a used K cup and it's working great. I also took a few voltage readings: mainly the output of the 12VDC regulator which is just fine and also some AC & DC readings of the air pump output. I wanted to get some baseline measurements to compare against once it starts working poorly again.

My question for anyone that has taken the time to read this is whether you think I might be on the right track now and, if so, what component(s) on the power board are most likely to suffer thermally-induced failures. I can't simply swap in the board from my parts machine because it's totally different in that generation.

If I can reproduce this problem, I intend on trying to isolate the faulty part with some freeze spray. I'll post a follow up if I have any success on my own. Thanks for any assistance that anyone might be able to provide.
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Re: Keurig B60 slow flow problem & repair experience

Postby jbviau » Sat Apr 20, 2013 9:23 pm

Wish I could help! Just wanted to say welcome and compliment your "clear to even a less-than-handy guy" writing style. Best of luck.
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Re: Keurig B60 slow flow problem & repair experience

Postby dweeezil » Sat Apr 20, 2013 9:58 pm

Thanks. I figured I'd follow up on the state of my machine.

Since I submitted my original posting only an hour ago or so, my machine has reverted to "dribble mode". One other symptom of this mode I forgot to mention in my original post is that the system doesn't seem to be able to sense the end of the brewing cycle properly in this mode. I suppose that makes sense if the problem is caused by the failure to produce sufficient brewing pressure; if the brewing pressure is low, there won't be much of a drop in pressure when the air is being pushed through. I can fool the computer into terminating the brewing cycle by rotating the "offset" pot on the upper board counter-clockwise.

At this point, in order to minimize the variables at play, I've unplugged the machine and am going to let it sit until it cools to room temperature. In my experience, that may be an overnight wait; it keeps everything hot for a long time if the water isn't drained! If my hypothesis is correct, it will work just fine once it cools off.

I realize I forgot to mention one other thing in my original post: I did actually replace the pressure sensor from my parts machine, but it made no difference. I also tried the entire top board from the parts machine and that also made no difference. I've switched back to the original top (display) board. My newer machine's top board is labelled as revision "S" whereas my old parts machine's is labelled as revision "C". Clearly they've been making a LOT of tweaks to these machines over the years! I figured it made sense to stay with the newer hardware where possible.

Stay tuned... Oh yeah, and if anybody had any information regarding the adjustment of the "offset" and the "gain" pots on the upper board, I'd love to hear it.
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Re: Keurig B60 slow flow problem & repair experience

Postby EmmJayEff » Sun Apr 21, 2013 8:48 am

dweeezil,

Three quick questions:

1. How well does your B60 pump out just hot water with no K-Cup installed in the K-Cup Holder?

2. Have you taken a paper clip to the K-Cup Arm needle port and to the K-Cup Holder (after taking it apart) needle port?

3. Is there water in the tube leading up to the Pressure Sensor circuit board?


Here is the Air Pressure Sensor schematic for one of my B70 machines if it helps:

http://home.comcast.net/~michael.flynn3 ... 051712.pdf

One word of caution is that I am a little unsure of the value of the VR1 potentiometer. Mine was marked “105” which should equate to 1 Megohm, but that seems like it is orders of magnitude too large for the associated circuitry.

The duty cycle of the 12 V square wave applied to the Air Pump is varied to keep the voltage at J17-5 at or below 1.45 Vdc.
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Re: Keurig B60 slow flow problem & repair experience

Postby dweeezil » Sun Apr 21, 2013 6:41 pm

EmmJayEff,

Good questions, but first, I'll say that I'm kind of at my wit's end. I no longer think the problem has anything to do with the electronics driving the air pump. After the machine slowed down again, I let it cool down and it didn't work any better. I'm beginning to think that something I do when I disassemble the machine in-between tries is making it work properly for awhile. As to your questions:

It seems to pump just great during a brew cycle with no K-cup installed. That behaviour is what made me keen on looking into the pressure sensor and the tube leading to it.

One of the first things I did was to try cleaning the (3-port) needle that pierces the K-cup. I was a bit concerned about the forward pressure in the check valve above the needle but my parts machine's check valve seemed to have just as much resistance. Plus, it pumped just fine when no K-cup was installed.

There is no water in the tube leading to the pressure sensor and it appears there never has been any water in it.

I'm a bit concerned about water in some of the various tubes. In particular, there's usually a little water in the tube connected to the bottom of the front solenoid. In my machine, that tube connects to a 4-port tee which I don't think I've seen in anybody's diagrams yet. I'm fairly certain the latest version of the B60 doesn't have that tee. To that end, I've photographed it and labelled the source of each of the 4 tubes:
Image
The tube on the left that comes from the bottom of the front solenoid usually contains a small column of water. That little column of water seems to rock back-and-forth when the machine is idle. I suppose it's responding to subtle changes in pressure due to the heater cycling on and off.

In any case, I'm open to any other ideas.

- Tim
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Re: Keurig B60 slow flow problem & repair experience

Postby desulfator » Mon Apr 22, 2013 9:28 am

The air motor pressure/speed seems to be governed by an air pressure sensor on a separate board than the microprocessor that make the judgement. on how hard to drive the motor.

I would reseat the harness connectors involved that run between them. If those connectors are not gold plated, the contact surfaces may have been affected by heat/humidity/age.

I would also check the voltage supply to both sensor board and main board.

Good hunting
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Re: Keurig B60 slow flow problem & repair experience

Postby jbviau » Mon Apr 22, 2013 9:37 am

dweeezil wrote:...first, I'll say that I'm kind of at my wit's end...In any case, I'm open to any other ideas.

There's always the dump! :twisted:

Seriously, I have a lot of respect for you and others who know your way around inside these machines, but it seems pretty clear to me that they're designed to be disposable. Anyway...

dweeezil wrote:I no longer think the problem has anything to do with the electronics driving the air pump. After the machine slowed down again, I let it cool down and it didn't work any better. I'm beginning to think that something I do when I disassemble the machine in-between tries is making it work properly for awhile.

What do you think could be happening during disassembly? Some sort of jostling?
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Re: Keurig B60 slow flow problem & repair experience

Postby desulfator » Mon Apr 22, 2013 10:01 am

As a general rule, when I discover problems in connectors, I cut them out and solder the wires directly to the board.

Connectors are great for assembly lines, but in time they can be the bane for interconnectivity.
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Re: Keurig B60 slow flow problem & repair experience

Postby EmmJayEff » Tue Apr 23, 2013 8:10 am

dweeezil,

Check your Private Messages.
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Re: Keurig B60 slow flow problem & repair experience

Postby dweeezil » Tue Apr 23, 2013 8:25 am

desulfator wrote:The air motor pressure/speed seems to be governed by an air pressure sensor on a separate board than the microprocessor that make the judgement. on how hard to drive the
motor. I would reseat the harness connectors involved that run between them. If those connectors are not gold plated, the contact surfaces may have been affected by heat/humidity/age. I would also check the voltage supply to both sensor board and main board.


That's my understanding, too. As EmmJayEff noted, the pump is driven by a variable-duty 12V square wave to control the pressure. Clearly the feedback mechanism is the pressure sensor on the upper board but I've got no idea why kind of signal it sends to the lower (power) board which actually drives the pump. It could send some sort of analog signal, digital signal, digitally-encoded analog signal... who knows? Somehow or another, the result is the 12V square wave from the lower board. I must admit that I've not yet done a plug/unplug cycle of the connector on the lower board in my machine. Obviously, I've unplugged/plugged the connector on the upper board a bunch of times. The connectors appear to be simple tin-plated pins.

I've also not done any voltage probing of the upper board. I can see from EmmJayEff's schematic, it has a 12VDC feed to power the op-amp and to drive the sensor network circuit. I'll have to measure that.

jbviau wrote:What do you think could be happening during disassembly? Some sort of jostling?


That's the $64K question, isn't it? I've been letting it "just run" for the past day and the pressure has gotten pretty bad. I'm clearly due for another round of disassembly/testing this evening in order to probe the voltages near and around the pressure sensor network. As a reminder, during this exercise I've been running it with the outer shroud removed. Whenever I need to expose the upper board, I always drain the water before removing the top of the machine. That operation likely drains all the water from the entire plumbing system. I've had a hunch that somehow it's the draining part of the operation that causes it to work well for awhile.

dweeezil (me) wrote:It seems to pump just great during a brew cycle with no K-cup installed. That behaviour is what made me keen on looking into the pressure sensor and the tube leading to it.


After further observation, I must correct myself and say that "just great" is an overstatement. At this point, the flow without a K-cup installed, although it looks to be solid, is clearly slower and less forceful than it ought to be.

Thanks for the ideas. This gives me a bit more to go on this evening when I take off the top again and expose the upper board for probing. I'll likely do a seat/reseat cycle of the connector on the lower board. I do have an extra wiring harness from my parts machine so I can replace it completely if necessary.... I'm not giving up on it... yet :|

- Tim
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Re: Keurig B60 slow flow problem & repair experience

Postby dweeezil » Wed Apr 24, 2013 10:50 pm

Figured it was time for a followup...

I've been lazy the last few days and have simply left my machine unplugged when not using it. In general, it has worked pretty well. There's something about letting it cool off that is helping it. I've also proven that the air pump can generate a lot more pressure if necessary. As you all might realize, the pump is run at a higher speed during the end of the brewing cycle (the "air puff") to clean out the K-cup. I can simulate the end of the brewing cycle by pinching the host from the air pump to the boiler and releasing it. The computer thinks the pressure change is the end of the brewing cycle. If I do this when it's in "slow flow" mode, the resulting speed-up in the air pump greatly increases the flow through the K-cup which proves the pump is capable of supplying the required pressure if necessary.

I'm now, finally, going to disassemble it again and examine the connector on the lower (power) board. I'll also take a few more voltage measurements while I've got the cover over the lower board off. Since I've swapped out the upper (display) board and it made no difference in the machine's performance, I'm back to thinking there's some issue on the lower circuit board. Unfortunately, there a whole lot of stuff there... optical isolators, diodes, transistors, etc... and I don't have a replacement to try in its place.

Did I mention this is driving me krazy???? :evil: Aaaargh...

- Tim
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Re: Keurig B60 slow flow problem & repair experience

Postby EmmJayEff » Thu Apr 25, 2013 8:41 am

dweeezil,

The fact that your B60 performance improves after letting it cool off (I assume that this also entails un-plugging it from the AC outlet) points to a leaky Forward Pneumatic Solenoid Valve. When the machine is plugged into the AC outlet, both solenoids are powered with 12 Vdc and the valves are open for 99% of the time. This allows the valve seats to collect contaminants (mostly rust). When the brewing process is initiated, the valves are "closed" by the removal of the 12 Vdc signal which allows a very wimpy spring to try and push a plunger into the contaminated seat. Leakage should be expected.

Here is a Tube Routing diagram for my B60 machine if it helps:

http://home.comcast.net/~michael.flynn3 ... 111712.pdf


When your Air Pump starts running, try pinching off the tube labeled "Bottom of Front solenoid" in your picture above. This should allow all of the air pressure generated by the Air Pump to enter the Water Heater (assuming you have no leakage out of the Air Pressure Sensor).
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Re: Keurig B60 slow flow problem & repair experience

Postby dweeezil » Sun Apr 28, 2013 9:24 am

EmmJayEff wrote:dweeezil,

When your Air Pump starts running, try pinching off the tube labeled "Bottom of Front solenoid" in your picture above. This should allow all of the air pressure generated by the Air Pump to enter the Water Heater (assuming you have no leakage out of the Air Pressure Sensor).


I'll give that a try. I did a few "try to blow through it" tests but it seemed that the front one sealed up pretty well when it was closed. I do have a couple of spare solenoids I could try, too. Maybe the solenoid loses its capability to block the air once it warms up.

I'll be trying these tests later this evening. Thanks for the idea!
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Re: Keurig B60 slow flow problem & repair experience

Postby GetSet » Wed May 01, 2013 7:37 am

Sounds like pinching off that tube is an idea worth pursuing. I was also wondering though - even when the brewing cycle is running slowly, when it eventually completes, does it yield a cup of coffee that is the correct size that you selected, or is it smaller?
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Re: Keurig B60 slow flow problem & repair experience

Postby dweeezil » Sun May 05, 2013 9:34 am

GetSet wrote:Sounds like pinching off that tube is an idea worth pursuing. I was also wondering though - even when the brewing cycle is running slowly, when it eventually completes, does it yield a cup of coffee that is the correct size that you selected, or is it smaller?


Regardless of show slow it was brewing, the final cup size was always just fine, however, when it really slowed down, the controller didn't realize that the brewing cycle was finished. There must not have been enough pressure differential for it to detect the end of the cycle.

With that said, however, I'm glad to report that my machine appears to have been fixed by replacing the front solenoid. I feel rather foolish for not realizing what was happening earlier but here's the rationale:

I did "test" the front solenoid early on in my diagnosis of the problem. My test, however, consisted of removing the solenoid and blowing through it (by mouth) to see whether it appeared to be sealing correctly. As others have pointed out in the various repair threads, it takes a lot of pressure to force the water through the K-cup. In fact, it's difficult to blow enough air into the tube (by mouth) to simply force the water, by itself, through the exit needle.

Furthermore, during my testing of the front solenoid, I never removed it. It looked to be in very good shape with no obvious signs of corrosion. When I finally removed it, however, there were obvious signs of minimal corrosion that weren't visible while it was installed.

When I got the suggestion by (re)check the front solenoid, I initially thought it wasn't the problem. The reason is that my testing consisted of pinching off the tube on the front solenoid's exit side (the bottom of the solenoid). I figured, after all, if the solenoid was leaky, what did it matter which side I pinched off. The reason I tested by pinching off the exit side was because the tube connecting the front solenoid to the tee connected to the rest of the pressure circuit was so short that there was no room to pinch it.

I finally decided to disconnect the front solenoid completely and manually operate the tube with a small clamp during the brew cycle by letting it open during the topping-off phase and then by pinching it during the brewing phase. Eureka! It brewed just fine. The front solenoid must have had an internal leak (inside its body) rather than simply letting some pressure leak past the internal seal. I think this is a very important failure mode to consider when repairing a machine.

As I said, I feel rather stupid for not catching this earlier; even if only accidentally. I had gotten 2 replacement solenoids but only replaced the aft one (which doesn't really even matter much for the proper operation of the machine) and ignored the front one because it showed no obvious defects. My original intent was to simply replace both of them, regardless, but I got lazy and skipped the front one because it looked so clean.

The lesson here is that the solenoids can leak internally into their body and that can't be detected by pinching off the output side.

I've been using the machine for about a week or so since I posted my last followup to this thread because I wanted to make sure the problem was solved and it clearly is.

That said, however, you knew there had to be a "but" :) , there's one other thing about its operation that concerns me. Although I didn't mention it earlier, I've been using the EZ-Cup product lately (a pretty good product, by the way, and I may post a review of it) and it seems that brewing through an EZ-Cup requires pretty much the maximum amount of pressure the air pump can muster. I'd say it requires even more oomph than most Extra Bold K-cups. When brewing with a properly fully-packed EZ-Cup, in some cases, after starting the brewing cycle, the air pump is clearly being cycled completely on-and-off. It does, however, maintain sufficient pressure to complete the brewing cycle in a reasonable amount of time. When brewing with a medium-strength K-Cup or one of the stronger Marley's "Real Cups", the brewing flow seems to be a bit more consistent and I've not noticed the cycling on-and-off of the air pump.

My question is whether this cycling of the air pump is a normal part of its operation during brewing cycles which require maximum air pressure?

Finally, I'd like to thank the other participants in this forum for all the great information; particularly the original "B70 Thread" and all the great information contained there. I think I'm ready to put my machine back together!

- Tim
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