Bogner alchemist resistors

nunonaos · Post by **nunonaos** » 23 Mar 2019, 14:16

Hello,

Can anybody help me out
What is this brown thing covering the resistors? Could it be on purpose when assembling the amp or are the resistors starting to fail?
I've mesured them from the bottom of the board and they are ok, on the top of the board i don't get any readings.

I'm looking at these because my bogner alchemist is changing channels on it's own.
I've looked at a schematic and noticed that these resistors are in the path that gives 3.3v, witch is the voltage for the microcontroler that changes the cannels.

nunonaos · Post by **nunonaos** » 23 Mar 2019, 14:20

I realise this isn't a pedal but the real question is about the resistors

Intripped · Post by **Intripped** » 23 Mar 2019, 16:16

That brown thing looks like glue, put there to increase the stability of those standing resistors

alexradium · Post by **alexradium** » 24 Mar 2019, 08:17

over time the glue can become conductive and create problems,the only way to know is checking out the various power rail voltages.

Jered · Post by **Jered** » 22 May 2019, 04:03

If your Alchemist is changing channels on its own its time for new power tubes and they need to be matched and biased correctly. Service manual says bias test points at 350mV but this isnt entirely true, it depends on your tubes, You need to read your plate voltage and bias at 60% plate dissipation and your switching will be stable. I learned this the hard way

lead2203 · Post by **lead2203** » 22 May 2019, 05:45

The power tubes have nothing to do with the channel switching. Could be anything from dirty jacks to something wrong with the switching power supply....or a bad solder point somewhere. With the amp on ...poke around with a chopstick or something like that and see if you get anything to happen. There's a few things to check here ....but if you don't have enough experience it's probably best to take it to a good repair guy. There are some things you can really mess up if you don't know what you are doing, like the FX section...one wrong move and you could take that out ...so be careful. Good luck

Jered · Post by **Jered** » 23 May 2019, 06:20

Im no EE, but that was my thought exactly. Power tubes cant be the problem, but after replacing relays didnt help I replaced the main board. Still had the switching problem. I finally called Line 6 and they knew exactly what I was talking about, told me how to fix it, and I havent had the problem since. The folks at Line 6 were fantastic, very helpful. Bogner not so much, they dont even consider this to be a "Bogner" and offer no support for the Alchemist WTF? It says Bogner right on the front right?

lead2203 · Post by **lead2203** » 23 May 2019, 11:57

Well... this is more of a line 6 product. Line 6 asked Reinhold to design and also licence his name for the product but Bogner had nothing to do with building it or much else...so the guys at Bogner wouldn't really know about problems or repairs of it. But cool you got worked out!!
What was the fix for it. It would be cool if someone comes across this thread with the same problem has an answer and can help fix his .....

Jered · Post by **Jered** » 24 May 2019, 05:09

The fix was just as I said. New tubes biased at 60% plate dissapation. As per the folks at Line 6

lead2203 · Post by **lead2203** » 26 May 2019, 03:43

That's odd, doesn't even make any sense. Did they give you a reason for the power tubes causing this?? I don't see the relationship to the channel switching to the power tubes. Unless it's heat related maybe...it's just odd but cool it fixed it. It's actually a cool amp once you figure out how to dial it in. Reinhold had a video up of me demoing it at the amp show but I can't find that video anywhere. Got some cool Gary Moore type tones out of it.