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Tektronix 2235 repair thread

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mnementh:
Yeah, well... my problem is not go/no-go, but one of noise, which I blame for a RAM error in the POST (Tek 2230, not 2235). I want to bypass the prereg entirely so I can determine if it is the source or just a victim of oscillation further down the line. So yeah, I wanna get pretty close to right on. ;)

mnem
*poit!*

mnementh:

--- Quote from: bd139 on December 10, 2018, 07:52:27 am --- :-DD

Trick is you don’t need exactly 43V. Anything around that but less than the trip voltage works nicely :)

In fact it seems to run around 35V fine.
--- End quote ---

I see what you guys are saying... at first I thought David's post was contradicting yours, now I realize he wasn't talking about the prereg and you're both coming to the same point by different routes. LiPo Storage charge is 3.7-3.8V/cell; With the three 4S packs I have handy that's 44-45.6V. Or I could do similar with 2 of my 24V drill packs. Should be good through a dim bulb tester I'd think. Now I need to drag it out and actually DO it instead of just thinking about it.


Yeah, yeah... I know. I should treat myself to a nice old Lambda CC/CV supply that can do it just by twisting a knob; what kind of TEA addict am I.  :palm:

mnem
*ZZZzzzzZZZzzz...*

David Hess:
They are contradictory.  The inverter will run on 35 volts but the outputs will not be regulated.

mnementh:
Well fine then... guess I need to read up on the "Principles of Operation" part of the service manual I bought so many years ago.  ;D

mnem
"Electrons may be very, very tiny; but when they gang up on you they ALWAYS win." ~me

David Hess:
On the 2213/2215 which have an earlier version of this power supply, operation is more explicit.  There are two adjustments; one controls the regulated output voltage and the other controls the headroom which is the voltage across the inverter transistors which keeps them operating in their linear region.  On the 2235, the headroom voltage is fixed by the switching preregulator.

The 4-channel 22xx oscilloscopes extended this design with a separate transistor used as the linear pass element and the inverter transistors run in saturation.  I suspect matching of the two transistors operating in linear mode in the 2235 design caused problems with transformer balance although that does not seem possible with a two transformer saturable inverter; the parts list does seem to indicate that they were used in matched pairs.

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