Fender Auto bias circuit

[loudthud]

Well, the internal combustion engine is all the same from the beginning but they keep adding all kind of electronics around it and I don't see anyone to object their new cars so maybe we'll have to live with it.
I was wondering if anyone could kindly save the software from the uCU (if it's readable and not locked)?

It's not an issue yet, but when one of those little computers in your car fails, you might not be able to get a new or rebuilt one from the manufacturer. Even if you could find one at a wrecking yard, it won't work in your car until it gets programmed at a dealer so that the other computers in your car recognize it's serial number. Otherwise, you probably won't be able to drive your car or even get it started.

In the case of one of these amps, it will probably need to be modified to run without the bias board, or just scrapped.

[Leo_Gnardo]

Well, the internal combustion engine is all the same from the beginning but they keep adding all kind of electronics around it and I don't see anyone to object their new cars so maybe we'll have to live with it.

Don't see anyone? YouseTube star Scotty Kilmer speaks for us who don't appreciate the so called "evolution" of cars that are more computer than car. "They're bound to turn into endless money pits." New Mercedes have no fewer than 75 computers. Not a typo. 75 computers, in one car, to make it work. Same is happening with farm equipment. When it won't work without all the computers happy & in sync with each other there's no choice but to have the dealer work on it. Expensive, time consuming, and did I mention extremely inconvenient. If your dealer doesn't have the part, or isn't hip to the latest kink in the software & how to fix it, you're up the creek. Car owners, yeh maybe you can get a rental or maybe if you're lucky a loaner from the dealer. But if you're a soybean farmer stuck with 1200 acres to harvest, and your dealer's 200 miles away, and doesn't know f@^#-all about how to deal with your John Deere's computers & software, well brother you just lost the farm. The days of fixing it with bailing wire & chewing gum are over. Why a simple item like a bass amp must be subject to the same nonsense is beyond my understanding. Keep It Simple Stupid!

[Enzo]

I think it is simple. You can still buy a used Deere A and keep it running. We have people thinking they have to adjust their bias every few minutes or the world will end, and people cry when some amp comes out without an adjustment. So they put in an automatic bias feature. Don't like that? Fine, buy a used old Bassman head and a cab. No one says we HAVE to buy the latest high tech thingy.

[Leo_Gnardo]

I think it is simple. You can still buy a used Deere A and keep it running. We have people thinking they have to adjust their bias every few minutes or the world will end, and people cry when some amp comes out without an adjustment. So they put in an automatic bias feature. Don't like that? Fine, buy a used old Bassman head and a cab. No one says we HAVE to buy the latest high tech thingy.

That may be true with vintage amps. Today's youngsters are less and less interested in them. Unless you have a smash-bang "collector's item" like a Vibroverb just like the one Stevie Ray played through, the general run of oldie but goodie amps are losing value. When young Guitar Johnnie can plug his guitar into his computer and generate sounds to his liking, what need does he have for vintage. Fender's newest all solid state Twin replacement looks like it's taking the world by storm. Surely smaller & more portable versions will appear soon.

With cars & farm equipment & similar items, it's a different story. The supply of good used equipment is dwindling due to the usual action of rust, accidents, and other attributes of entropy. I was lucky to find a well-maintaned 2001 Jeep Cherokee a couple years ago to replace the '96 version that had served me well for 14 years. But how many other people are going to be content driving a 20 year old car? In farm gear, there are some astonishing improvements that can maximize production through applications involving GPS. But all that takes - computers. Modern gear involves a ton of computers just like those new Mercedes cars. Those who can afford it, of course they'll take advantage of it and prosper. Except when it breaks down - Mean Time Before Failure tells us, the more complex the system the more likely it is to break down. If you don't have a couple of spare harvesters in your barn, and your neighbors are all busy with theirs, you're up the creek. Call the bank, tell 'em to take the farm, move to the city & live under a bridge, there's your future Mr Farmer.

[GainFreak]

With cars & farm equipment & similar items, it's a different story.

You're right. We're talking only one uCU here and even if it's obsolete and you can't find it you can always throw the bias board and make a regular bias board. Not so with a car.
However if the bias board uCU is baked you can always replace it but without the software it's useless. That's why I suggested to save it if possible (although Fender must have taken appropriate measures) in case you need it in the future.

[nickb]

We can only speculate at the reasons for Fender having this board. I would guess it's attractive to the user to know that if a tube fails he'll know which one to replace and also that he'll be able to do it himself. So they're here to stay so might as well have a strategy to deal with them rather look at it in horror. Here are a few ideas that spring to mind to get the ball rolling so feel free to add or amend.

Reseating and cleaning relevant connectors is always a good starting point. Especially as these rely on accurately sensing a few mV. A bad ground will wreak havoc.

Try swapping the tubes around to see if the problem follows the tube, or just try known good ones. Don't forget about potential bad contacts or dry joints on the sockets.

Simplify. It's pretty easy to disconnect the board and lash up a conventional bias arrangement to see if things are stable without the board. I heard of a case where an intermittent speaker cable caused the board to misbehave and this would show up more easily with the board out of the picture.

Check the sensed voltages on the inputs to the board and then the processor. Get some super fine needle tipped probes for your meter. They are a god send. If those are wrong there's no hope for the poor little micro.

Look and see what is happening with bias voltage outputs. If any are off look to see if it's correct coming from the micro. This is often a pulse width modulated signal but some e.g. Bugera use a multi channel DAC. If the micro is dead you'll need to replace the board unless you have a copy of the binary and have a programmer and can replace just the processor.

Micros seldom misbehave of themselves, they just react to the inputs and that includes the power rails so check them too. Bad decoupler caps can cause unpredictable behavior. Bad micros are most often completely dead.