advice for new toy *ahem* tool HP1220A oscilloscope

[NTkiller7000]

Hi folks, I just picked up an oscilloscope on the cheap, a HP 1220A. Guy advertised it as dead ("Won't power on") and I took a chance. Got it out of the box, and plugged it in. Mind you, I've never personally messed with a scope before, so I had no idea on how to operate it. Turned it on, and nothing. I then popped the cover for a look, and it was really clean inside, with no obvious damage. turned it back on, and I saw the CRT cathode light up. "This thing can't be dead" I said to myself, so time to RTFM! OK, Online manual says set up scope as shown in picture and turn on, but the picture is unreadable (craptastic scanners!). Anyway, I ended up using some educated guessing to set up the scope, turned it on, and pressed the beam finder button. Huzzah, it worked! I guess the guy responsible for testing the scope didn't know how to run it either. After putting the lid back on, I proceeded to send a signal to it for testing, using a multimeter lead in between one input and the scope's test point on the front. Got a nice square wave going on the face after playing with some settings. I'm currently waiting for a pair of probes to show up in the mail. Is there anything I need to be aware of about this scope? I'm going to use it for working on a CRT TV motherboard, so no digital signals to speak of. How come when I feed it a square wave it doesn't draw the lined between the crest and trough of each wave? And does anyone know where I can find a high quality scan of the manual? Thanks!

[stj]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

consider a x100 probe for tv work, the x10 probes usually arent rated over 300v

[R_J]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

You might want to find an isolation transformer also, a lot of crt chassis are hot, not isolated from the a/c line

[NTkiller7000]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

I picked up tp6100 probes off ebay, hopefully they'll be good enough for what I want. I'm not going to be poking around high voltage, so it should be fine. An isolation transformer should not be necessary for this particular TV, since it has proper line isolation on the board.

[eccerr0r]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

Sometimes the rise/fall slopes don't show up very well when the signal's edge rate is extremely fast. If you bump up the horizontal sweep (or, namely, reduce time per division on "modern" 'scopes) you should get to a point where you should be able to see the up/down edges, unless that edge transition rate far far exceeds the bandwidth of the 'scope.

[NTkiller7000]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

Sometimes the rise/fall slopes don't show up very well when the signal's edge rate is extremely fast. If you bump up the horizontal sweep (or, namely, reduce time per division on "modern" 'scopes) you should get to a point where you should be able to see the up/down edges, unless that edge transition rate far far exceeds the bandwidth of the 'scope.

I set the time division to where the scope showed 2 waves on the screen, and the only way to see the edges was to turn intensity WAY up (don't do this for more than a split second, screen burn hazard!) when connected to the 2KHz square wave reference on the front of the scope. Maybe the transitions are too fast for the scope to pick up, or it's the fact I'm not using a proper scope probe (waiting for the probes to show up in the mail)

[eccerr0r]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

Actually an improper probe will slow down or otherwise distort the slope, making it more likely to be seen. It's more of the former. But you shouldn't be concerned about it, you can fill in the blank in your head.

Also don't worry about seeing the full wave if that's not what you want to see, likely it's near the transitions that's the "interesting" stuff and if you just show the transition, it can show more of what you need.

[NTkiller7000]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

Gotta dumb question: can I turn down the cathode heater to prolong the CRT life? I remember when I had the cover off, I saw the cathode was getting orange hot. Is that too hot, or normal? The reason I'm asking is I've never seen a CRT TV or monitor get their cathodes as hot as this thing does.

[eccerr0r]

Re: advice for new toy *ahem* tool HP1220A oscilloscope

All vacuum tubes should somewhat glow when heated, even VFDs. So it's normal it's orange. It should NOT be white however, but it's hard to gauge what is normal for a particular tube as different tubes have different amounts of the filament exposed, and have different normal operating temperatures.

Usually you can't change the voltage without affecting the secondary anode voltage anyway, as both tend to use the same transformer. A resistor in series may work.

Actually, heater failure is the least of your concern. Gas diffusion from a leak and cathode emulsion loss can't really be helped are the 'wear' that happens to CRTs over time, other than phosphor burn. As you said earlier, keep the intensity reasonable. Turn the 'scope off at nights, weekends, long periods of disuse, etc., and it will last a long, long time. I have several old CRT oscilloscopes and they still work just fine.