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 It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more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. ?
