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FIXED HBL8451UC/01 Bosch wall oven, third board, still random events

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
Model Number
HBL8451
Brand
Bosch
Age
1-5 years
I have a Bosch HBL8451UC/01 30" wall oven. It was a direct replacement for a previous 800 series model we put in when we remodeled the kitchen 3 years ago. We went with all Bosch appliances...regretting that decision...but for now, I'll just focus on the wall oven.

After 2 years of usual performance, the oven starting acting strange. It would randomly shut down during preheats...sometime shut down during regular baking. Other times it would work just fine. Oven mode didn't make a difference. At other times, it would act as though someone just hit the "conv bake" button, flashing 325...waiting for you to press enter to initiate preheat (even though no one is in the oven).

So...I figured this was something bad happening with the control board...pretty much all there is to this unit.

I ordered a replacement board from Bosch, about $175 and installed the board. For a week or so it appeared to function just fine...however, at some point the oven would no longer engage heating (just the 2 tone this isn't working sound) unless the lights were turned on...either by opening the door or my a button press...then, you can bake, broil, whatever you want. Then about 4 weeks ago, the display panel went dark. Buttons would make the 2 tone sound, but nothing would turn on. It required 2x cycles at the breaker, and it would light back up and it would work...again with the "light on" caveat. It happened again 2 weeks ago, so I called Bosch and asked to RMA the board.

Got a new board. Working well day 1. No more "light on" necessary. Next day, tried to preheat to 350, display indicated preheating, however, never heard a relay click and nothing happened...no heating. Lights also would not work at all. Power cycled, came back to normal function. About and hour later, the phantom button presses started.

Never seen an error code, even in service mode.

So...I think I have a ghost.

But I'm up for any other suggestions. The 3 "bosch" guys in our area have horrible reviews, and its never fun when you can't recreate the event.

Thanks for the read!
-NitDawg
 

rickgburton

Appliance Tech - Moderator
Staff member
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Messages
44,788
Location
Murray, Utah 84107, United States
What is the part number of the board you just replaced? Bosch is not a popular brand in my area. Thermador/Bosch/Gaggenau has made it very difficult to get any service information on their appliances. Do you still have the tech sheet and wiring diagram?
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
11020741 is the p/n

Here is the info under the hood...it's still just trying to turn itself on.
 

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NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
Each board had a slightly newer eeprom, but all with weird random issues... So if it's not the board, I'm not sure what to check...line voltage was fine at initial install, I can't imagine that causing these issues.
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
Ok, I couldn't wait until the AM.

2 keytails on this control board...one was maybe not fully seated...I reseated both and I'll see what happens!
 

rickgburton

Appliance Tech - Moderator
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If the ends look discolored try using a pencil eraser to clean the ends.
 

rickgburton

Appliance Tech - Moderator
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Any chance I can get you to take another picture of the wire diagram and post it here. Parts of the other one are just too blurry for these old eyes. Thanks.
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
Here's the link to the PDF (https://www.amazon.com/clouddrive/share/lpmmvSyh0fJaeUISHIJmcJ4TTQUW5EtogsLFNvNs69g) so you can zoom in on the different areas...if you need more, let me know!

Here's a JPG:
20180730_212314.jpg

I think this applies to another thread where you asked them for the wiring:
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
So the phantom presses are gone. However, baking this morning I heard relays cycling, with momentary loss of fan and heating. Display never flashed nor did the oven power cycle...simply stayed the course.

This evening, I went to preheat... And like I described before, I could set a temp, however lights would not turn on, nor would the oven heat. After a reset via entering the service mode and exiting, oven function returned... But again, I get the relay/turning off/back to normal thing again...video here:

https://www.amazon.com/clouddrive/share/s82yC19VzEYp4jFzcb3rvAloEJW3B92EF7HKmYrdSZT

So bizzare.
 

rickgburton

Appliance Tech - Moderator
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I read your first post again trying to get a timeline on the boards but it wasn't that clear. It's been my experience replacing a PC board will not fix a problem with another pc board even temporarily. This is what you said in your first post:
NitDawg said:
For a week or so it appeared to function just fine........Then about 4 weeks ago, the display panel went dark.
OK here's where I'm confused. Is that suppose to say "For a month or so....." ? If the board worked for a month then had the exact same symptoms as the first board, the board is bad again. If you replaced the board and got the same symptoms again, the new board is bad.

When replacing the boards a lot of wires get moved. Look for a pinched or almost broken wire. Make sure none of the pins in the connectors are starting to back out of the connectors and not making a good contact.
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
Board 1: Oven installed Jun 2015. Worked just fine until beginning of 2017. Issues were with oven shutting off (like pressing the cancel button, not a power loss) and the phantom touches.

Board 2: Ordered July 2017, not sure when I installed it...probably Aug/Sep. Board 2 worked fine, except in order to engage any cooking feature the lights needed to be turned on...either through the button, or opening the door. Otherwise, the oven behaved until May/June. LED panel would go completely dark...not a power issue since the buttons would still respond to presses with a double beep. 2x power cycle the oven would come back to life and work until it decided to go blank again (this happened maybe 3 times?)

Board 3: Ordered July 2018, installed July 2018. The "need your lights on" requirement went away. However, oven now will on occasion heat up with random events of relay clicking and heating turning off, but not losing power. Also, inconsistently, the oven will accept a preheat temp, however the lights will not turn on, nor will the oven or fan engage. This is fixed with a reset. Also, in this mode (no oven light, not heating, etc.) the relays are no gos in the service menu...a reset and you can then cycle the relays.

I have all 3 boards. Its possible that the Board 1 was ok and it was the keytail that was the source of the issue. Board 2...the oven light thing was very strange. Board 3...well, its different in its own right, lol.

I find it odd that I have 3 bad boards. And the work wine sometimes but not other times drives me insane...its very hard to duplicate certain things. Here's the wired board. There's not much to it, but I can certainly inspect all the wires and connectors. I had to use new stand-offs on the new boards (the originals were not removable) but that's the only thing that is different.

20180106_110548.jpg

There is an Option Code in the service menu, although the limited service info doesn't say if that needs to be set...on some of the previous models you did set this based on your model...but again, doesn't explain the working sometimes but not other...
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
20180804_104712.jpg

20180804_104722.jpg

Great idea! I've never had to touch these with the new boards, but I noticed the ring connectors coming off the red and black posts were very loose. Both red and black wires are damaged...I think this explains the intermittent power...it was losing 110... I'm heading out of town, but I'm going to replace these and tighten them down. Stay tuned.
 

rickgburton

Appliance Tech - Moderator
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OK, keep in mind that it is extremely rare for more than one part to fail at a time unless there's a direct short or power surge. Here's what I see; The second board only fixed part of the problem and the problem that wasn't fixed by the second board (lights) was fixed by the third board. That tells me the problem is still with the board. After looking at the pictures of the terminal block wires, especially the black wires, I'm wondering if you have three good boards. Is there a ground wire on the center post with the white wires?
 

NitDawg

Premium Member
Joined
Jul 30, 2018
Messages
13
Location
North Carolina
Yeah, both of the load lines have some damage close to the post. The black wire is brittle and you can see the debris from the wire. The lines coming in are nice and tight, under a star washer and nut, then 2 ring terminals that go out to the oven... With a star washer and nut on top of that ...those are incredibly loose. The neutral post just has the neutral line in and 4 going out. The ground is secure. Well, I have all 3 boards...so I will replace these wires, tighten up, and see.

20180804_193342.jpg
 
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