HP Unobtainium IC revisited (1725a)

am kinda back where I started becasue two scopes are better than one.

it. Beside my eyesight going to the bats (not dogs), I was totally unfamil iar with the unit and the modification was under the aluminum plate on whic h the vertical output amp lives.

tion 101 on the parts donor. Don't look it up, 034 is the multimeter on top and 101 is an interface for a data acquisition unit.

here would be the least amount of alignment needed that way, plus who knows what else they did to it, it worked, but not quite fine. Here's what chann el A looked like on the internal calibrator with a 1X probe :

n the plate capacity be that damn different ? Nope, this is channel B :

r with the vertical preamp instead of what had been changed. I am a mad mod ifier from way back so I know better. I also know what DC coupling is, unli ke that guy, who came up with this :

ode where you could see a haze of a waveform when you adjust the position. Not quite the accuracy I was looking for...

cation thus :

built, and it saves components. So I used it on specimen number two. Of cou rse it was supposed to be this :

laying around. Looked like pretty low capacitance so I took them.

half the time and the sweep time knob takes a pipe wrench to turn, the ampl itude is low. About 33% low. It is the same on both channels. I am pretty s ure I can adjust it there, but I would rather get the gain where it is supp osed to be, especially since the position controls just barely take the tra ce off screen. It should have a bit more range than that.

z square wave, even though I can't get it to lock right now, appears to hav e a hell of alot of ringing in it. Also in chop mode, you can see a bit too much that you are not supposed to see.

thing is a toy. What I am thinking at this point is to change the 1,000 ohm resistors to about 1,500. Or should I go higher ?

edback obviously. I find it hard to believe the gain is lower using that MO SFET. I do realize that it takes more voltage to turn it on, but that doesn 't necessarily cause that.

te voltages were too low. I tied it to the original land for the IC pin on the amp board and it is alot closer. The print calls for 40 volts and I got 38 and change. Of course I tried jumping out the resistor but as expected it did nothing for the differential gain, just lowered both plate voltages some.

y ideas. I'll find the right resistors sometime later and see about getting that gain up. Then I want to do something about the ringing but first mayb I'll get it to trigger. I suspect that as I've read on a bunch of these un its, the switches are just dirty. I'll give them a good bath of course. Hop efully that does it.

ith these units. I have my little board under the aluminum, which is right where part of option 101 goes. I have no room for both. I could try to make the thing smaller so it can go on the top, but since the original was on t he heatsink, I figure the modification should be as well. It would be damn tough to get these parts to fit down there.

and have the thing still work ? It would do nothing without it connected. N ot just not a trace, not even a dot at the left side of the screen.

'll just go back on my meds - Budweiser. (probably do that anyway...)

Sometimes you can't beat going back to basics. Lenny

Let's not take that too far th0ugh. I meant to ask you about thart cassette deal. Any moves on that ? Did you consider the 1 Khz square wave method I said ?

Anyway, I finally gave this HP a bath. It's like a new nmachine. Now rememb er there is the good one, and ?I thought it was all f***ed up, but not I se e that we had shitty probes. Long story, but these babiers are working bett er thaan I thought. I had a shitload of pictures of 1Mhz square waves and s hit, but the camera f***ed up and they are lost. I willget more.

I decided fukit, see if I can get the gain right. No good, the end of the r ange of the vcontrol is not even close. I see how they design, and I do not like it. The gain seems like they are shunting the signal, it is all one s ided. I could design better than that. Of course that is all over the place . My assocoiate just got stumped checking bias and shit on an old vintage u nit, what it was it that the bias control had too much range, and it don't go below zero. Of course that is why I am here.

I have stuck the thing to the aluminum for now. In fact now that...

Oh. I have solved the option 101 problem. I disconnected all kinds of thigs and now know what must remain connected. I have the board off to the side now and it won't be bothering anyone. However I now know that I must increa se the values of those resistors, and I THINK I should bump them from 1,000 to 1,500 ohms. Now that I see how this thing is, I am thinking of going ev en a bit higher. Extra gain is usually easier to handke than the lack there of.

I did do something though. I got this buzzbox welder, or I did. I loaned it to a buddy of mine and he still has it, I don't care. But the rollaround s tand fits this HP really nice so now I got that, the Fluke 8050A on top of it (option 035 ?) and the Wavetek 111 on the shelf underneath (option ZZZ).

It's looking pretty good actualy. And my dude brung me the 422.

/sending befroe this becomes the new bible

am kinda back where I started becasue two scopes are better than one.

it. Beside my eyesight going to the bats (not dogs), I was totally unfamil iar with the unit and the modification was under the aluminum plate on whic h the vertical output amp lives.

tion 101 on the parts donor. Don't look it up, 034 is the multimeter on top and 101 is an interface for a data acquisition unit.

here would be the least amount of alignment needed that way, plus who knows what else they did to it, it worked, but not quite fine. Here's what chann el A looked like on the internal calibrator with a 1X probe :

n the plate capacity be that damn different ? Nope, this is channel B :

r with the vertical preamp instead of what had been changed. I am a mad mod ifier from way back so I know better. I also know what DC coupling is, unli ke that guy, who came up with this :

ode where you could see a haze of a waveform when you adjust the position. Not quite the accuracy I was looking for...

cation thus :

built, and it saves components. So I used it on specimen number two. Of cou rse it was supposed to be this :

laying around. Looked like pretty low capacitance so I took them.

half the time and the sweep time knob takes a pipe wrench to turn, the ampl itude is low. About 33% low. It is the same on both channels. I am pretty s ure I can adjust it there, but I would rather get the gain where it is supp osed to be, especially since the position controls just barely take the tra ce off screen. It should have a bit more range than that.

z square wave, even though I can't get it to lock right now, appears to hav e a hell of alot of ringing in it. Also in chop mode, you can see a bit too much that you are not supposed to see.

thing is a toy. What I am thinking at this point is to change the 1,000 ohm resistors to about 1,500. Or should I go higher ?

edback obviously. I find it hard to believe the gain is lower using that MO SFET. I do realize that it takes more voltage to turn it on, but that doesn 't necessarily cause that.

te voltages were too low. I tied it to the original land for the IC pin on the amp board and it is alot closer. The print calls for 40 volts and I got 38 and change. Of course I tried jumping out the resistor but as expected it did nothing for the differential gain, just lowered both plate voltages some.

y ideas. I'll find the right resistors sometime later and see about getting that gain up. Then I want to do something about the ringing but first mayb I'll get it to trigger. I suspect that as I've read on a bunch of these un its, the switches are just dirty. I'll give them a good bath of course. Hop efully that does it.

ith these units. I have my little board under the aluminum, which is right where part of option 101 goes. I have no room for both. I could try to make the thing smaller so it can go on the top, but since the original was on t he heatsink, I figure the modification should be as well. It would be damn tough to get these parts to fit down there.

and have the thing still work ? It would do nothing without it connected. N ot just not a trace, not even a dot at the left side of the screen.

'll just go back on my meds - Budweiser. (probably do that anyway...)

I did like the square wave idea and was thinking about trying it but sudden ly work got very busy, so as long as duty calls I have to leave this for a Saturday afternoon. Lenny.

The HP is backburnered for now. Actually my associate says he might find a third, if so and it doesn't need the same thing, fine.

I modified it by adding 680 ohms to tha 1 Ks. I saw those 680s and said "sE lf, those are perfect". Problem is that when I fired it up then it owuldn't trigger. I DID give the thing a nice bath in LPS2 and it did seem to impro vr things. I was going to say OK, I'll just set the gain and be done with i t for now, but the gain onb the preamp wouldn't go high enough. I wasn't to o crazy about doing it thart wqay anyway.

I had a bunch of pivcutre sI thought but the card got corrpupted somehow. I had a fairly decent 1Mhz square wavw on it, one I wiggled and juggled enou gh to get all the old comnections connectioning.

The other "good" HP ike this might need some help. ZSeems like I get better response on this one than on that one. Next time I am going to hok it up w ith clip leads, screw the probes. I have to look see about that Wavetek 111 I got, how it reacts to a 50 ohm load, and align it with that. Maybe put t he whole damn front end from this is there, because as much as I tried, the thing just didn't seem to come out right. ringing and all this,. even in t he 1Khz square wave.

I got an old 422 on a lend/lease type of deal, a Hameg and a B&K. They all work. And now we might be getting a 7633. Not sure about that though.

Anyway, got ta get a few things out of here myself. the profit potential in the HP is not great really. I know it is among the fastest analogs out the re, but so what. I don't need to carefully exmine the eye pattern on a CD p layer or whatever, hell even scoping the Ysus in a plasma is no problem for the old 422, or even the B&K which no matter how shitty it is, still works . When it didn't it was some bad connections in the vertical output. Didn't need a single component.

More later. I am not co,mpletely throwing it out, butit is getting on my ne rves. Why the hell would it stop triggering ?