Yep the Tek prereg SMPS is pretty well behaved except when it isn't.
IIRC didn't you and I discuss MOSFET gate Miller capacitance some while back which is the trap when repairing the Tek prereg as often what looks like a compatible MOSFET for their repair has too much gate capacitance and the switching is troublesome as the driver hasn't sufficient grunt to overcome the gate capacitance.
I do believe we did. Another one of the infernal constraints of the universe come to bugger up our engineering attempts.
The killer was if you don't drive it hard enough and quick enough, then it exceeds the SOA while temporarily in the linear region resulting in what sounds like it firing a shotgun at you. I have ear protectors and safety glasses when dealing with SMPS now
I think on the 22xx supplies it's not actually sourcing electrons into the gate that was the problem though which came from the TL494, it was getting rid of them afterwards hence the 2n2907 sitting in front of it...
This is of course why it blew the 2n2907, the diode and the MOSFET during the failure cycle
No not that one but a Tek repair thread Vince did where member Per Hansson gave us lessons about Miller capacitance:
https://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/msg1824401/#msg1824401
Well worth a read.
Unfortunately also the thread where helpful member oldway crossed swords with Simon and despite it being a private slanging match oldway is with us no more.
Oh yeah I remember IOldway... what a jerk he was when he posted on that 2215 topic to complain about my long posts. I wish him a long and painful death.
I am still waiting for the replacement brass collet you said you would turn on a lathe with your friend Dubbie, to fix the broken one on the time base know ! Kiwis are all show and no go, promise just promises !
Been 4 years now so I gave up on it
But that's fine, because I gave on the scope altogether, it's hopeless. This erratic auto-brightness feature I could never figure out how to fix despite great efforts. That alternate sweep daughter board is not meant to be desoldered, butchered it. Tried to fix t.. butchered it even more... Can't socket it to work on it as the connectors with the proper pitch just don't exist.
I apid 40 Euros for it, no power. These days with the shit economy old analog scopes or worse nothing and right now there is a WORKING 2215A for... 40 Euros, what I paid ofr my broken one.
There is routinely 2000 seires Tek scopes in excellent cosmetic and working condition, showing traces on the screen, for 50 Euros.
I t makes absolutely zero financial sense for me to keep trying to fix it. Much easier and valuable and useful to me as ... as parts mule. For one, it will donate a few of its knobs to fix the broken ones on my 2232. The small ones for vertical and horizontal position control, that kind. They break, shatter like glass when you try to remove them...