# Bosch HMC80251UC microwave oven has dim display



## tmittelstaedt (Nov 7, 2018)

I've done this with a few video display panels and several computer motherboards. Sometimes it works sometimes it doesn't. The devil is in step #11 however. You have to order online and sometimes the caps come different sized and won't fit. And many places have minimum orders on these parts. Failing electrolytic caps are the bane of the computer industry and there seems no rhyme or reason to them - I've opened up 6 year old PC's exact same age same model and one inside had all bad caps and the other inside had all perfect ones.


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## NitrNate (May 27, 2010)

i've replaced quite a few capacitors on control boards to fix issues. i've replaced mosfets, switches, relays, bad solder joints, etc. as well. the trick is trying to figure out which component is causing the problem. capacitors often times swell so that's an easy visual indicator.

as far as getting the parts, you can get everything on ebay, typically shipped from china. i always buy extra since most of the stuff is so cheap. if you need one, get a 5 pack. i've broken stuff trying to re-solder on a board so it's always good to have extra.


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## waynezack (Oct 29, 2020)

latest problem in 80251. i 've replaced the main board twice. finally got the NEW midfied board. replaced the door switches many times. now a new problem this week the microwave stopped working and the turntable stopped at the *same time*.  convection works but no turntable. microwave sets timer and counts down , light bulb works and fan work but no heat. coincidence at the same time these two events happened ?? is the turntable controlled by the main control panel? i know microwave is controlled by main board could it be my control board again? any ideas?


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## ctc911ctc (Feb 13, 2021)

oberon148 said:


> I'm posting this problem and solution, in case it's useful to others. My Bosch microwave display was dim to the point where it was practically unreadable. This is apparently a known problem with this oven, and the usual solution is to replace the control board, which I understand is now no longer available. Elsewhere on the net, you will see suggestions about replacing capacitors on the display board to fix this. So that's what I did....but here's a step by step:
> 
> 1) turn off power! - the oven is built-in, so switch off the breakers
> 2) pull the oven from the wall - mine was attached to the matching wall oven as well as the wall cabinet, so I had to detach the wall oven to pull the stack out sufficiently to get at screws on the side of the microwave that hold it to the stack
> ...


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## ctc911ctc (Feb 13, 2021)

Hi,

Bosche HMC87151UC uWave 3 years old - dim display just as indicated here. 










I read this note and replaced a 470uF cap next to a small rectifier circuit that was damaged. I tested the diode and the transistor all seemed fine. 
I replaced the cap which was damaged (bubble top) and then cleaned up the burned varnish.










Put it all back together and there was a brighter display (I think) for a few seconds and then back to the dim screen. WIthout a schematic (I am past tracing components to make schematics) I reached my patience limit. I am going to find a new board or a replacement.

Many have opined that the heat from the oven is baking these caps. I beleive that there is a design flaw that is resulting in an over-current condition for a component and then resulting in heat/failure of the component. Though the cap was bubbled, it still tested correctly.......changed it anyway...........if I learn more I will post more


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## ctc911ctc (Feb 13, 2021)

DEFINITIVE - Fixing the Bosch Microwave Model HMC87151UC - Definitive 
Model - HMC87151UC
Year - 2015
Description - Cabinet installed Microwave and Convection Oven

Very common with this brand is the LED starts to dim and then Diminishes to a very low level. Many people posted that within this model it is the 5vdc supply. This is not correct. The LED panel is connected via a ribbon cable which carries 3 discrete voltages as well as a few digital interface connections. Starting with pin 1. we have

Pin 1 - F+ (this is a differential voltage that controls the brightness of the LED
Pin 2 - F- (the other part of the differential voltage that controls the brightness of the LED
Pin 3 - VH - (high voltage, nominally 40vdc, for the LED panel overall power)
Pin 4 - GND
Pin 5 - 5vdc ( this is the ttl power for the board)

With the LEDs very dim here are the voltages of the interface cable


PIN / brightness selection =>123 F+3.153.483.68 F- 1.752.032.24 VH40.440.240.2 GND--- 5vdc5.455.455.45


I then looked at the traces and determined that the problem must be with the components on the V+ or V- that are marked for some reason F+ and F-

What I found was a little 220uF cap in this circuit. 


























Here are a few views of this cap, once it was replaced here are the proper voltages:



PIN / brightness selection =>123 F+6.57.077.53 F- 2.162.753.25 VH40.440.240.2 GND--- 5vdc5.455.455.45


So, in closing the differential voltages controls the brightness of the LEDs. There is a cap that effects these voltages on the V- (called F-) trace next to the transformer. This cap is a

220uF 25V dc device


QED


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## ctc911ctc (Feb 13, 2021)

Continuing......................

The circuit in my opinion was pulled down by a shorted capacitor. The amount of current through this capacitor was so small that it never got hot enough to burn through and open up. Hence, the capacitor turned into a pull-down resistor for the differential voltage. This resulting in a dimmed display. All is well now.

I was re-energized to fix the board after I bought one on-line (From Sears of all places) which in the on-line picture showed the display, the panel and the *control board!* Yea! When I received it, it was used (dirty on the face of the keyboard interface) and there was *NO CONTROL BOARD!*. My guess is that the guy before me ordered the assembly and then returned the system he was replacing with the old stuff. Very evil people out there. The people at sears did not check (or know what to check for) before putting the returned assembly back into inventory. As you may imagine I was upset and determined not to be tricked, so I sent it back (sears paid for the shipping) for a full refund. I then, now energized, decided to put to use my old EE training to work and got it done. 

Thank you for reading and making the therapeutic experience of documenting all of this valuable for at least one person; you!


SEARCH ENGINE ENABLING ENTRIES

HMB5051/02 Bosch 00771183 Part Number: AP5953625 MFG Part Number: 00771183 Bosch HMC80251UC bosch dim display


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## Tsmm1 (Jun 26, 2021)

ctc911ctc said:


> DEFINITIVE - Fixing the Bosch Microwave Model HMC87151UC - Definitive
> Model - HMC87151UC
> Year - 2015
> Description - Cabinet installed Microwave and Convection Oven
> ...


Question on the CAP, you state the cap is 25v dc, yet your pic is a 16v device. Are you upgrading the voltage to prevent further burn outs?
I am on 2nd burnout, now I wish I had saved the first board.
thanks


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## pablotex (Jun 26, 2021)

Tsmm1 said:


> Question on the CAP, you state the cap is 25v dc, yet your pic is a 16v device. Are you upgrading the voltage to prevent further burn outs?
> I am on 2nd burnout, now I wish I had saved the first board.
> thanks


I have the same dim display issue, and also want to confirm in order to fix it, do we need to replace the CAP (circled out in the pic) from 16v to 25v ?

Thanks!


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## Tsmm1 (Jun 26, 2021)

pablotex said:


> I have the same dim display issue, and also want to confirm in order to fix it, do we need to replace the CAP (circled out in the pic) from 16v to 25v ?
> 
> Thanks!


Replace the 16v 220uf 105c with a 25v part. 
Mouser PN 710-860240475007.
Replace the 470uf 25v 105c with this part
Mouser PN 80-ESL 477MO25AH9AA, this is a 10k hour capacitor where the OEM cap is a 2k hour cap.
Replacing both of these should give us a few more years between brown outs. 
parts less than $10 including extras. Since I kept my original board I now have a spare for repair and wait for the next time. With luck something else will wear out before the display.


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## Marty10 (Sep 13, 2021)

Replaced the 220 and 470 on the board in our Bosch HMC87151UC with a successful outcome. This was after replacing the board about 2 years ago. Unfortunately, I'd disposed of the old board but very happy to have found this thread and replaced the capacitors as recommended, appreciate the effort that people went to in sharing this solution 👍.


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## bob22 (May 28, 2008)

Well done, more persistent than I might be. Is this an over the range unit or countertop?


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## twofirstnames (Sep 30, 2021)

ctc911ctc said:


> Here are a few views of this cap, once it was replaced here are the proper voltages:
> 
> 
> PIN / brightness selection =>123 F+6.57.077.53 F-2.162.753.25 VH40.440.240.2 GND--- 5vdc5.455.455.45
> ...



Thank you!!!


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## Bonsai Lumber (Nov 18, 2021)

Tsmm1 said:


> Replace the 16v 220uf 105c with a 25v part.
> Mouser PN 710-860240475007.
> Replace the 470uf 25v 105c with this part
> Mouser PN 80-ESL 477MO25AH9AA, this is a 10k hour capacitor where the OEM cap is a 2k hour cap.
> ...


This is great! Thank you so much. I now have the parts on order. I believe the second Mouser PN is 80-ESL477M025AH9AA. There may have been a Zero - Oh switch.
Is it possible to show which 470 cap needs to be replaced? It looks like only the 220 was circled in the picture.

Thank you


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## Bonsai Lumber (Nov 18, 2021)

Bonsai Lumber said:


> This is great! Thank you so much. I now have the parts on order. I believe the second Mouser PN is 80-ESL477M025AH9AA. There may have been a Zero - Oh switch.
> Is it possible to show which 470 cap needs to be replaced? It looks like only the 220 was circled in the picture.
> 
> Thank you


This is a great thread. I got the parts from Mouser and fixed the problem. 
I actually ordered an extra of each. If anyone is going to fix theirs, I'd be happy to send it on free of charge. Just send me your address.


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## daggerfs (Jan 4, 2022)

Thanks so much for the detailed info. I replaced the two capacitors on mine ( HMC80151UC , and I believe that HMC80251UC uses the same board) and the microwave bounced back to life.

For whoever is interested, the two capacitors needing replacement are circled out below:









The original 220uF capacitor is 16v on the board, but I replaced it with a 25v one just to be safe.


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## huesmann (Aug 18, 2011)

That 470 is obviously bulging (failed); hard to tell on the 220 due to photo angle.


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## daggerfs (Jan 4, 2022)

huesmann said:


> That 470 is obviously bulging (failed); hard to tell on the 220 due to photo angle.


Yep, hard to tell. I had to do a simple multimeter test and the capacitor showed a couple thousand ohms instead of going infinity (of course, this was in circuit and should not be definitive). My guess was that the capacitor was too small to show any physical changes. After desoldering it, multimeter confirmed that it went bad. I guess it might be a common issue on the board given ctc911ctc’s excellent analysis above.


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## gregmac (Mar 10, 2011)

I just did the same repair on mine: replacing the 220uF and 470uF capacitors. The 470 was bulging, and the bottom of the board looked very similar to the photos ctc911ctc posted. The numeric display was just barely visible in the dark, and the text line was always unusable.

After removing the old caps, the capacitance test on my multimeter fails to get a reading from either of them.

I replaced with 35V capacitors as that's what I had available. Even at brightness setting "3" the display is still a bit dimmer than the stove display, but it's fully usable now.

Thanks everyone, especially to ctc911ctc for the great analysis and daggerfs for pictures.


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## Steve in Denver (12 mo ago)

oberon148 said:


> I'm posting this problem and solution, in case it's useful to others. My Bosch microwave display was dim to the point where it was practically unreadable. This is apparently a known problem with this oven, and the usual solution is to replace the control board, which I understand is now no longer available. Elsewhere on the net, you will see suggestions about replacing capacitors on the display board to fix this. So that's what I did....but here's a step by step:
> 
> 1) turn off power! - the oven is built-in, so switch off the breakers
> 2) pull the oven from the wall - mine was attached to the matching wall oven as well as the wall cabinet, so I had to detach the wall oven to pull the stack out sufficiently to get at screws on the side of the microwave that hold it to the stack
> ...


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## Steve in Denver (12 mo ago)

Just to add, I upgraded all 25V caps to 50V rated, the 220uF 16v was upgraded to 220uF 25V. Display works great now. 2 bad capacitors.
Make sure you have a solder sucker....
Also, bought all my capacitors at MicroCenter. $1.39 each for the 470's. Thanks to all that posted!


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## Bnqishomedepot (10 mo ago)

Thanks for the write up. Been living with the dim screen problem for a few years, finally got around to fixing it with this guide. Ordered the Mouser parts listed above and replaced the two most suspect caps, as well as 1x other 220uF and 2x 470uF caps that were on the board since I was already in. Works a treat.


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## JerryCan (10 mo ago)

Chiming in as well. From Canada. Ordered the 2 caps from mouser (got 2 of each since it is so cheap). We bought ours in 2016 and it started dimming in 2018. Wasn't looking forward to the repair bill, but earlier this year, I found this page. Had to wait for the parts since they were back ordered. Did the swap just now and it works superfine. Happy wife, happy life... 

Thank you OP. You are Legend.

BTW, my caps weren't bulging, but the back of the PCB definitely showed some heat affected areas.


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## tutu_beater (4 mo ago)

Very grateful I found this thread as my Bosch microwave LED light has not been working for years but last week it finally died completely. I called up the Bosch service repair line and they said they'd send someone out today between 12-3 but the guy never showed up which is just as well because they were going to charge $300 for the service call that would go towards the cost of repair! I managed to get the control board after watching this youtube video: 




I ordered the replacement capacitor parts but while I was trying to put the outer cover back over the microwave, there was a spark when one of the wire clip contacts (I'm assuming it was the HOT line) contacted the surface of the oven so I was wondering if anyone would know what the replacement part for that plastic clip is called as it looks like it's melted enough I won't be able to reconnect the circuit board now.









After some searching it looks like the part is a wire-to-board connector but I'm not sure how to narrow the search down to the exact part.


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## clyde1 (4 mo ago)

Is the 152UC the same configuration? Thank you.


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## handyJL (2 mo ago)

Thank you guys for sharing your experiences here! I got a Bosch Built In Microwave and shortly after we got the place, the display dimmed to almost non-readable. After almost 4 years of enduring the dim light, I finally got up and started look into how to fix the problem. After reading the postings, I managed to take down the control board and sure enough, the two capacitors are bulging at the top. I'll take the board the the electronic store locally and see if they can offer me some advises besides getting the replacement capacitors. Thanks again!


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## handyJL (2 mo ago)

Hi guys, I changed the capacitors as both of the 470uf and 220uf are bulging. reconnected to power, the microwave display light are back to normal brightness, but right after 12:01, there is E - 01, the next line says call 1-800-944-2904. Anyone encountered this? Thanks!


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## handyJL (2 mo ago)

problem solved. The solder was not properly done. added some flux and formed the proper ball of solder, the error message disappeared.


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## Redcatfish (18 d ago)

I know this is an old subject but will post a of photo of my board to show the capacitors. One of them I think may have blown itself apart, not sure what to think.


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## Tsmm1 (Jun 26, 2021)

That is most definitely blown apart. Replace it and the one next to it, it is also bulging. You can see the domed top.
Order your parts from Mouser, they are listed in earlier posts. Circled parts in photos are what you want to replace. 
Don’t make the same mistake as one poster, ensure everything is unplugged prior to working on the unit and fully reassembled prior to plugging in again.
Good luck!


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