Pro Audio Design Forum

My feeling is that the solenoid is good and that it's me. When I move the solenoid piston the stroke is smooth. There are other solenoids so I can measure the voltage there and see if this one matches. I thought solenoids were current operated though. I know the one in the Neumann cutter head suspension is a constant 12 VDC with variable current driving the solenoid.

Well if its constant 12V and the coil resistance is fixed I'm not sure how you vary the current other than using pulse width modulation.

Most simple solenoid circuits have a higher current for pull-in then reduce the current after a delay to lower heat.

You also may be way past the optimum mechanical adjustment and increasing it somehow makes it less.

Picture (and schematic) worth a thousand words...

One of my 'scope probe center conductors opened probably mid-cable.
I was able to get both ends apart.
The center conductor is a single strand smaller than wire-wrap wire. Tiny.
With my luck the break is probably in the middle.

This one is about 10 years old so I guess its time to order another.

JR. wrote: ↑Fri Feb 23, 2018 2:44 pm Received my replacement control board for the coffee roaster, so replaced it and just did a new roast. The hardest thing about this repair was paying for the new control board ($200+) but a new roaster is $1600, and I roast a batch every 5 days.. I did one roast blind, but seeing what is going on is better.

I didn't look into replacing the cooling tray fan yet... that requires a complete tear down and doesn't really affect the roast quality (something else for my to-do later list).

JR

Today I swapped out the fan.... It has been several years since I opened up the roaster and there was some interesting looking detritus inside (it wasn't growing but almost looked like it was). The replacement fan had the wires coming out at the wrong angle for the notch in the base, but no problem, that's why we have wire cutters that can cut plastic.

Coffee is now cooling promptly after the roast.

I cleaned the window on the roaster front cover and could see inside for the first time in years...

JR

mediatechnology wrote: ↑Tue Mar 20, 2018 4:28 pm Picture (and schematic) worth a thousand words...

Maybe more like 250 words. This is it. I think it has some more info on the solenoids somewhere but below is basically it.

How old is the pinch roller?
Is it hard?

If it was on a Studer I’d say it’s done. It has a shiny band where the tape contact is. But the capstan is chrome plated. Smooth and shiny unlike a Studer. The pinch roller looks about the same as it did when I got the machine.


I’m not measuring enough pressure on the spring scale when the solenoid engages. Right now the pinch roller isn’t even making contact with the tape. It’s way off and I’m not sure why.

I am corresponding with someone who knows these machines. I asked about the pinch roller condition.

Well it didn't take long for my next repair project to reveal itself.

My slick peltier based dehumidifier, I bought hoping a solid state dehumidifier might be quiet enough to run in my bedroom at night but nooooooo. The minute I plugged it in I knew the fan would be the weakest link, and not silent.

Well this morning the fan started making bad fan noise and when I shut it down it refused to restart properly making a squealing noise.

Time for a better replacement fan... More info after I tear it apart.

JR

PS: Coincidentally I just replaced the bean cooling fan in my coffee roaster, fans suck. Last century when I designed a fixed install amp for PV with fan cooling, I upgraded the 2 speed fan, adding a third speed (off), to extend MTBF service life....

I heard back from my M15 guy. He says the pinch roller looks fine and the surrounding mechanical assemblies look good too. It looks like it's all the adjustments. Back to banging my head against the wall.