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Test Equipment Anonymous (TEA) group therapy thread

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Vince:

--- Quote from: tautech on May 23, 2022, 10:26:56 am ---
--- Quote from: bd139 on May 23, 2022, 09:48:01 am ---
--- Quote from: tautech on May 23, 2022, 09:37:02 am ---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.

--- End quote ---

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  :-DD

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  :-DD

--- End quote ---
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.  :(

--- End quote ---

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 ! :-DD

Been 4 years now so I gave up on it  >:D 

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...

Neper:

--- Quote from: Cerebus on May 23, 2022, 11:23:23 am ---"There's food poisoning and then there's M&S food poisoning."*

* For those not exposed to UK media: Parody of M&S's current ad campaign slogan.

--- End quote ---

From an article in Belgian newspaper La Meuse: "If you have eaten these sausages and suffered from fever, stomach cramps and diarrhea within the following 48 hours, take them back to the store for a refund."

https://lameuse.sudinfo.be/896896/article/2022-01-21/attention-si-vous-avez-mange-ces-saucisses-le-produit-ete-retire-de-la-vente?from_direct=true

Haven't seen anyone approaching an Aldi store with a bucket, though.  :-DD

med6753:
Holy crap. I sleep late today and the thread has exploded. I'm struggling to catch up.  :o

One comment then I need coffee. Unique food consumption. George Carlin once said: Americans will eat anything. If you served sauteed raccoon's asshole on a stick they would eat it. Especially dipped in butter.

Carry on.....need more caffeine then I gotta check my blood sugar and take my shot.  ;D

dl6lr:

--- Quote from: Neper on May 23, 2022, 12:12:44 pm ---
--- Quote from: Cerebus on May 23, 2022, 11:23:23 am ---"There's food poisoning and then there's M&S food poisoning."*

* For those not exposed to UK media: Parody of M&S's current ad campaign slogan.

--- End quote ---

From an article in Belgian newspaper La Meuse: "If you have eaten these sausages and suffered from fever, stomach cramps and diarrhea within the following 48 hours, take them back to the store for a refund."

https://lameuse.sudinfo.be/896896/article/2022-01-21/attention-si-vous-avez-mange-ces-saucisses-le-produit-ete-retire-de-la-vente?from_direct=true

Haven't seen anyone approaching an Aldi store with a bucket, though.  :-DD

--- End quote ---

Similar to one experience with a local market here. We bought frozen trouts just before weekend and found out that they where probably off, so we discarded them immediately. And mentioned it to the market on Monday. Reply was we had to bring them in to get a refund   :wtf: :-// Needless to say we were not there to get a refund, but to warn for possible food poisoning. And we promised to bring in any rotten fish the next time it would occur...

mnementh:

--- Quote from: bd139 on May 23, 2022, 09:48:01 am ---
--- Quote from: tautech on May 23, 2022, 09:37:02 am ---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.

--- End quote ---

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  :-DD

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  :-DD
--- End quote ---
EDITED TO CLARIFY

That's the FET in the prereg bolted to the side of the chassis, with the legs plugged directly into a MOLEX connector, right?

I over that one on my 2230 after rebuilding the HV multiplier section when I first got it; replaced it with exact same part, new from either SPHERE or NIP ECG/NTE with the same part number on the transistor off eBay. About every 3rd power-up, it would go into tic-tic failure mode; noodling around in one of the Tek groups yielded advice to replace with STF9NM60N (specifically plastic package TO-220, not the regular tab) and cut the legs short & solder/shrinkwrap the wires. Scope worked perfectly for nigh on a decade after that.

That was when I decided to go back to tinkering on my old analog schizz... between that circle-jerk and the unobtanium pot the thing used for menu navigation, I decided there was just too much fucking voodoo in digital scopes of that era. :-DD

mnem

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