Those numbers just don't make any sense.??? I pulled all the transistors AGAIN, desoldered and cleaned.? Tested them all with a meter, repopulate.??? Back to 23.5v....???
On Fri, Aug 30, 2024, 6:22?PM Bill Berzinskas via <bberzinskas= [email protected]> wrote: Replaced Q9, powered on and blew the fuse.? ?Replaced Fuse?+ Q9 again?+ pass transistor and no fuse pop.? ? Not sure if better, worse or just different :-)? Q9..? C = 22v B = 54v?!? (was 23.5v)
E = -17v.?
Q10..
C = 54v..? (was 23.5v)
b = 0.58v (up from 0)? E = 0v
Q11..?
C= 54.7 (was 23.5v)
B = -.64
E = 0
On Fri, Aug 30, 2024 at 5:48?PM Michael Bafaro via <m.bafaro= [email protected]> wrote: Bill, ? OK it seems that Q 9 has a base-emitter voltage of 38.5V which says that the base-emitter junction is open because a good NPN silicon transistor can only have a forward base-emitter voltage of 1V under extreme conditions.? Normally the Vbe is in the order of 0.7V. If the emitter or base connection of Q9 were open the emitter voltage will be dragged negative by R41.? That is not good for the pass transistor Q4 to see that much negative voltage because that will exceed the Vebo rating of the pass device which may degrade the Beta of the pass device.? Basically it will Zener the base emitter junction with that much reverse bias.? Typical Vebo is in the order of <10V which is in the absolute maximum ratings of the part.? A 2N3053 should work OK as the driver Q9.? Let me know how it goes. ? Mike ? ? That does make sense,?thank you for that explanation..? I do believe I've stated it backwards.? ? 22v appears on a 2n3053 that I've replaced at pin 3, which is actually the collector..? :facepalm:..? Remeasure / restate Q9..? ? On Fri, Aug 30, 2024 at 3:02?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? Lets back up a minute¡ If there is +22V at the emitter of the driver Q9 then there must be +22V at the base of the series regulator Q4 and you say that there is less than 1V ?at the emitter of the pass transistor Q4 and also no voltage at the top of R42 (the current sense resistor) then there is 22V across the base emitter junction of? Q4 and that can only be a failed device or some bad wiring or even a cracked runner on the board. A good NPN transistor has no more than 1V Vbe.? ??Does that make sense to you?? Or is the voltage at the emitter of the driver Q9 a negative 22V?? If the voltage at the emitter of Q9 is negative then what is the voltage at the base of Q9? ? Mike ? ? Ok..? I had a few bad transistors in the mix, but the one that was in the unit checks out ok.? ? ?I tossed a small handful to alleviate future issues.? ?
I spent a little time simulating this and from what I'm seeing this almost has to be a problem w/ the voltage divider / potentiometer.? ?I can do a lot of "shady" things in the sim and none of them give me issues like I'm seeing.? ?Removing R43 in the sim, or the pullup R45 seem to skew the voltages like I'm seeing.? ? ?The sim shows that the trimpot is kind of what "kicks things off", and the fact that I'm only getting about -1v here seems to further hint towards R43.? ? I don't have a 22.1k or even a 22k on hand, so I'll probably get creative to see what happens.? ?Resistance measurements on the pot itself look ok, i'm really hoping to not have to yank that thing.?? ? On Fri, Aug 30, 2024 at 11:58?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: I'll check these over lunch.? ?Interestingly, two of the original transistors in that spot cause the 3a fuse to blow.? ?Now sure if thats indicative of something else going on w/ a good transistor in the seat..? ? tbd.?? ? On Fri, Aug 30, 2024 at 11:43?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? 22V on the emitter of the driver is very strange.? It seems that the pass transistor Q2 has an open base ¨C emitter junction and a shorted collector base junction to come up with those voltages.? That would explain the ¡°on output¡± situation.?? An Ohm meter should be sufficient to check the status of Q2.? If your meter has a diode scale, that would give you a quick indication of the status of Q2.? ? I am thinking ?of designing an over voltage crowbar circuit to protect the -12.6 V supply from damaging sensitive circuits down stream of this supply if the regulator goes to an over voltage condition.? Some of the plugins appear to have a crowbar in just such a condition.? The filament of the flood gun is run from the -12.6V and in my case it went over voltage and it burned out the flood gun filament. ? ? Mike ? ? Thanks Michael,?
here's a recap what i'm seeing around the -12.6v line currently:?
?.65v at base of q11 sensor amp, .275v on collector.?? Driver has 22v on emitter, .27v on base and -.27v collector.????? Not much happening on the current limiter.?? 0v base.? ? On Fri, Aug 30, 2024 at 11:15?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK so you have the early version of the supply.? If you give me the voltages at the base of the driver transistors I can perhaps give you some more pointers. ? Mike ? ? correction, it did have the LAMP..? ?? ? My unit is 1615a prefix, it did have the zener and it was measuring closer to 100v instead of the expected 83 or whatever.? It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more permanent?solution as I've read about.? ?I can check that again this evening!? ?I stopped thinking about it after I got the?+100v supply up! ? On Thu, Aug 29, 2024 at 4:50?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? There are 2 versions of this supply.? There is an early version that has a neon tube as the reference for the +100V supply and a later version that uses a 9V temp compensated Zener that is floating.? That is the reference Zener is connected from the +100V rail and the base of Q4.? It may help to know which version you have.? From my schematic the +100 V is the master and the other supplies are referenced from it.?? The one I have has a serial number prefix 2101A and it appears to be made in the late 1981 or early 1982 time frame. This one has the floating 9V Zener. ? Mike ? ? Finished that up.? ?On the -100 I can adjust up to 96v, a little low but it is adjustable so I think I should come back to that later.??
On 248v I'm currently seeing 290v, and -12v I'm seeing -1.5v.? ? ?I reckon I could go after either of them given the dependencies.? ? Will grab some measurements in between or after work today.? ? ? On Thu, Aug 29, 2024 at 10:52?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Well, this is awkward.? ? I had replaced both Diff Amp transistors with the same part number.??
I just found that this package is actually reverse from what i removed!? ?using a dorky little? heathkit transistor tester, i found the pinout to be CBE when looking at it from the flat side.??
The center leg was bent towards the rear of the part, while the original part was bent toward the front.??
I reversed both transistors, and got -106 which i was able to adjust appropriately!? ? ??
Strange, but makes sense.? ?I have a few more of these buggers in the supply, so it sounds like I'll be sorting through that today.? ? Will report back in a bit.??
Thanks for the help ya'll!? ? On Thu, Aug 29, 2024 at 10:45?AM Frank Mashockie via <fmashockie=[email protected]> wrote: Also, don't forget about Gianni's HP e-book.? If I remember correctly, he goes into great detail about the 141T.? Here's the link.? They can be slow to download and I forget which section includes the 141T. ?
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