Repairing BOSCH B20CS30SNS/01 fridge

[jcdammeyer]

The more I think about this and the more I read, the more I think the reference to frequency as a control input is incorrect (by my definition but ok by someone else's definition). I think it is simply feedback of the real speed from the motor back to the VFD so the VFD can adjust the output frequency to compensate for slip.

The two pin connector is an input from the controller and is not in any way connected to the motor. The only connection to the motor is via 3 pins and frame.

1. Encoder feedback is a frequency.
2. Most VFDs can be set to use motor feedback from an encoder.

This should not be thought of as "Most VFDs" and there is no encoder feedback.

3. VFDs that drive Pumps commonly use encoder feedback to adjust for slip.

In the commercial world maybe but the two I have (in an earlier photo) do not have encoder feedback. They might well detect back EMF from the driven current to detect slipping. I doubt this compressor Single Phase to Three phase driver is that sophisticated.

It just seems too coincidental to conclude otherwise.

Unless you disagree with this assessment, my curiosity is sufficiently satisfied.

This is as far as I have gone with the reverse engineering. I can't easily remove the board from the plastic box as the heat conductive glue under the driver transistors and input diodes used for the voltage step up circuit are encased in this glue and stuck onto a metal plate which in turn is clipped onto the plastic box. So I can't trace from the bottom of the board.

Contrast that again with the full metal heatsink on the red Baldor VFDs or even the STMBL in the earlier photos.

Note here that the control input could conceivably be simple ON/OFF optically isolated or a frequency request in or even PWM in.

It's when I put the scope ground onto the ground side of the 100R resistor that it went up in smoke. After replacing that resistor the system no longer behaves as before so I broke something else too.

When the module was still in the fridge I measured the AC voltage across CN05B at 2.5VAC (RMS).

The power input terminals are marked N and P. There is infinite resistance between the N and the Ground pin. There is 10 MegOhm between the P and the ground pin. But the AC coupling may be a lot lower and I should have either isolated the scope ground or used an isolation transformer to so the scope would float and not conduct current through the ground pin. A rookie mistake. Or an old fart mistake in this case.

I'm sorry John, I can't think of anything to try beyond what you have done. Unless you can get better service info it may well be that your only option is part swapping (which I hate). I'd guess that swapping out the compressor is impractical though - certainly beyond what I would tackle. So that leaves you with the other boards and components. Almost like Russian roulette.

The single phase to 3 phase motor control modules are known to fail. Bosch part diagram #D608. I have one in a shopping cart at $492.86 at PartSelect.ca and can ship today if I order in the next 4 hours. Don't know what shipping would cost.

Not sure if I will do this or just get a new fridge.

 

[Susquatch]

The two pin connector is an input from the controller and is not in any way connected to the motor. The only connection to the motor is via 3 pins and frame.

Well that settles that! LOL!

Don't be so hard on yourself. You do WAAAAY better than most.

Ya, $500 plus shipping is a LOT to gamble. If it was under 200 I'd be a player but prolly not at 500 plus. Any chance it could it be returned?

I vote to cut your losses at this point too. You gave it a great shot.

 

[jcdammeyer]

The new replacement single phase to three phase compressor driver now has a Purolator tracking number. Appears to be coming from Calgary so will be here on Thursday.

This was the easiest decision assuming it fixes things. Why? Because any other fridge we want has at least a two week delivery.

I tested the opto isolator and sure enough it still works. Using my IR temperature probe the two power supply chips sit about 6C above ambient. However the processor also rises to 8C above ambient. I'm pretty sure that flash of burning resistor due to the high AC voltage coupled through the scope ground also fried a part or all of the processor. No holes. But still dead I suspect.

For my own stuff when I get a unit back with fried processor I just remove it, solder in a new one and install new firmware. Probably not that hard to get a replacement processor but firmware not so much.

Now fingers crossed that it was only the compressor driver that was defective.

 

[Susquatch]

The new replacement single phase to three phase compressor driver now has a Purolator tracking number. Appears to be coming from Calgary so will be here on Thursday.

This was the easiest decision assuming it fixes things. Why? Because any other fridge we want has at least a two week delivery.

I tested the opto isolator and sure enough it still works. Using my IR temperature probe the two power supply chips sit about 6C above ambient. However the processor also rises to 8C above ambient. I'm pretty sure that flash of burning resistor due to the high AC voltage coupled through the scope ground also fried a part or all of the processor. No holes. But still dead I suspect.

For my own stuff when I get a unit back with fried processor I just remove it, solder in a new one and install new firmware. Probably not that hard to get a replacement processor but firmware not so much.

Now fingers crossed that it was only the compressor driver that was defective.

Now we all wait. I'm praying with you.

 

[jcdammeyer]

Purolator arrived just after 2:30PM. Took a few hours after replacement and powering up the fridge in Super Cold mode to reach this temperature. But the fridge has been repaired.

 

[PaulL]

Most chillingly excellent!

 

[jcdammeyer]

Most chillingly excellent!

Thanks. Just sad that I toasted the original board which I think I could have repaired.
The replaced board was made in 2017. The original in 2008. The fuse is different but for the model and version number is the same. Made in China. With COTS type drivers and ICs. A perfect candidate for "Right to Repair".

If I step back a few years (OK, more than a few) I've run into this sort of thing before. I took Electronics 10..30 in High School. We learned basic electronics and these new things called semiconductors. Since I was in the Radio Broadcasting club doing both announcing and the electronics maintenance it wasn't surprising that my career after high school was a disk jockey job at a very small radio station; CJOI 1440 AM.

They had an automation system. Tapes, cartridges (like 8 tracks but pinch roller was in the machine, not the cart) and two big long tapes with even and odd time of day announcements. The reel to reel held the music, the carts the commercials. The selection of items was done with... get this... punch cards.

The IGM system (International Good Music) would read the first 3 columns of the card and preselect the device. Rotate the cartridge carousel to the right spot and load the cart read to play. Read the proper reel to reel.

Now if it was a Time Card with T00 in the first 3 columns it knew that a time announcement (even or odd) was next and once per minute the system incremented the cart with the time announcements to the next minute. But these were short. Often shorter than the time to sequence a carousel to the correct position and load a cart.

The system would read the card, eject it and read the next card's 3 columns and queue up that device. Then when the current song or commercial was done, the time would play and then the queued cartridge. No delay.

The system was broken. It would read the time card. Kick it out as expected. And then kick out the entire deck. All the commercials and music. Once the reader was empty it would default to the reel to reel player and just do music. Until the tape ran out...

Long story shortened is the system came with schematics and standard RTL logic devices. My education and hobby experience helped to solve the problem. During the evenings for the first 2.25 hours of my shift I had to play religious tapes. So I spent some time trouble shooting the machine that might cost me my job.

After finding a temperature sensitive RTL chip in the card reader logic section and replacing it the card reader went from reading the first 3 columns with a tick tick tick sequence to burp sequence easily 10x as fast. When the tick tick tick took too long the timer expired and ejected the cards to the end of the deck.

Fixed! But I didn't lose my job. They no longer wanted the automation system. The secretary claimed the Model 735 computer driven IBM Selectric Typewriter as her own typewriter and the Automation system was abandoned.

Without schematics and standard RTL devices it would have been very expensive to repair if at all.

 

[Susquatch]

Purolator arrived just after 2:30PM. Took a few hours after replacement and powering up the fridge in Super Cold mode to reach this temperature. But the fridge has been repaired.

Absolutely awesome news John! I have been holding my breath on this end hoping for that outcome! I feared the worst so this is a great outcome if you ask me!

 

[jcdammeyer]

The sad thing is this motor driver module is made in China. Other than where the fuse sits it's pretty well identical to the first one with even the same barcode ID for control type. Made in 2017 instead of 2008. There is no way it should cost $500. Lots of people along the way getting their cut.

Especially when it was possible to build up something like this which has two boards, two processors, fan, heatsink and more connectors for about $120. This is the STMBL and runs a 3 phase servo motor with encoder and either step/dir or serial protocol etc. The key to it was the transistor driver array which is now discontinued. I don't know if a replacement was found.

More on this in a CNC thread I'll start soon.

 

[jcdammeyer]

The STMBL motor driver in the photo presented in the previous post was developed and the code etc. is available in this new thread.

STMBL motor driver -- Electronics and Software.

This thread will be about the STMBL drive which is open source for both hardware and software. However it's poorly documented and now 6 years or so old. https://github.com/rene-dev/stmbl A link for getting started is here...

canadianhobbymetalworkers.com

 

[Tecnico]

Absolutely awesome news John! I have been holding my breath on this end hoping for that outcome! I feared the worst so this is a great outcome if you ask me!

+1

Been crossing my fingers for a good outcome, congratulations!

D

 

[jcdammeyer]

My Capacitor ESR tester arrived today. Checked a bunch of random caps in my junk box. They all appear to be good. Next step. Dig out the original 3 phase motor controller and check the caps and compare them with the new ones that came from Mouser. If any are off I'll replace them, power up the board and see if that 4.9V supply jumps up to what I read somewhere is supposed to be more like 6.8V.
Not that this will fix the board since I likely blew up the processor but it will create some closure.

 

[Susquatch]

My Capacitor ESR tester arrived today.

Which one did you get? Do you like it so far? Would you buy it again?

 

[jcdammeyer]

Which one did you get? Do you like it so far? Would you buy it again?

I didn't get mine from Amazon. My label isn't covered up like the amazon one and I got two sets of probes with mine. Price with shipping was about the same.

ESR Capacitance Meter, MESR-100 Auto Ranging in Circuit Tester for TV, LCD and Audio Board : Amazon.ca: Tools & Home Improvement

ESR Capacitance Meter, MESR-100 Auto Ranging in Circuit Tester for TV, LCD and Audio Board : Amazon.ca: Tools & Home Improvement

www.amazon.ca

To be honest I have no experience with ESR testers. The chart was crooked on the front but then I don't always get the sticky's down square either. Zeroing with the leads shorted does not result in 0 but in 0.002 or so. Not sure that's a real issue. The auto range and manual range appear to work.

I measured a brand new 220uF 35V which worst case, the label says is 0.170 Ohms. I measured it at half that. The data sheet for the device states 0.16 Ohm impedance. So I'd say this brand new one is pretty good. I'll measure the one in the power supply and report back.

 

[Susquatch]

I didn't get mine from Amazon. My label isn't covered up like the amazon one and I got two sets of probes with mine. Price with shipping was about the same.

ESR Capacitance Meter, MESR-100 Auto Ranging in Circuit Tester for TV, LCD and Audio Board : Amazon.ca: Tools & Home Improvement

ESR Capacitance Meter, MESR-100 Auto Ranging in Circuit Tester for TV, LCD and Audio Board : Amazon.ca: Tools & Home Improvement

www.amazon.ca

View attachment 28270
To be honest I have no experience with ESR testers. The chart was crooked on the front but then I don't always get the sticky's down square either. Zeroing with the leads shorted does not result in 0 but in 0.002 or so. Not sure that's a real issue. The auto range and manual range appear to work.

I measured a brand new 220uF 35V which worst case, the label says is 0.170 Ohms. I measured it at half that. The data sheet for the device states 0.16 Ohm impedance. So I'd say this brand new one is pretty good. I'll measure the one in the power supply and report back.

Thanks John.

 

[jcdammeyer]

So I pulled out the big one. It's within spec. Then a couple of the smaller 33uF 25V. Holy S%$t.
New one has an ESR of about 0.65 Ohms. The two I pulled are 16 and 18 Ohms. Since low ESR is important in switching power supplies it's not a surprise that these two (which are for the two low voltage supplies) resulted in what was probably a low voltage reading..
Had I waited one day and then just arbitrarily replaced the caps it's likely the compressor drive would have worked. As long as I didn't put the scope ground on the wrong pin.

Now I'd love to get one of the installed Lions Gate Bridge Lights back into my shop so I can measure the cap in that one and compare it to one that has maybe 10 hours.

 

[jcdammeyer]

Here's my last posting on this subject. Finally got around to installing the new capacitors in the defunct 3 phase driver. Connected it to the motor and of course it still doesn't work since I toasted the processor.

But. Now instead of seeing about 6.5 V across one of the 33 uF 25V caps I now measured 16V which is more in keeping with the drive requirements of the transistors used to make the 3 phase power for the fridge compressor.

So had I waited and installed the replacements that arrived the next day and not pulled out the scope I'd have had a successful repair.

Up side? There's always an up side. I now own a Capacitor ESR meter.

 

[jcdammeyer]

Hey, great to hear an update on your BOSCH fridge repair journey! It sounds like you've made some progress, even though there were a few hiccups along the way. That's the thing with DIY repairs, sometimes it's a trial and error process, but you learn and acquire new tools and skills along the road

And the fridge is still working...