#31
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As for the cap, I know I need one over 240V, but is there a particular value I should use? Also, should I parallel it with the current one or can I just find a 240V source and put the cap on it to ground? I've attached the section of the schematics with the C270 a 10uf 300V. The T207 is the Flyback.
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#32
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The waveform looks to be about 1.5 divisions peak to peak, so that could be either 7.5V or 75V, depending on whether or not the "5V/div" is taking the 10:1 probe into consideration.
75 vpp ripple on a 240V supply is a problem. 7.5V, not so much. The doubled waveforms might be caused by improper triggering. Make sure you are triggering on whatever channel the probe is connected to, and if your scope has a TVH trigger mode, use it. Try rocking the trigger level back and forth around zero, and see if that makes the trace clearer. I would start with the same value cap as you already have installed, and putting it right in parallel should be fine if it actually goes to ground. The attachment isn't showing up for me... |
#33
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The cap is connected the following way. There's a lead from the flyback to a leg of a diode, the other leg of the diode connects to a leg of a 150 ohm 2W, the other leg of the resistor goes to the positive side of the cap and a lead that connects the 240V around the chassis and finally the cap goes to ground. I'll have to find a local source for a 10uf 300V cap. The local Radio Shack doesn't have them in-store. Must be a place around here somewhere. Not looking forward to paying 7 bucks for shipping of a single cap.
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Pioneer SX-1080, Pioneer PL-115D, Pioneer CT-F9191, Pioneer RG-1, Wollensak 8050A, Akai 4000DS MkII, Pioneer CS-05 & Polk 1.2TL Denon 5803A, Pioneer DVL-700, Pioneer CT-W603RS, Toshiba HD-A3, D-Link DSM-520, Dish VIP-722, Polk 1.2TL, CSi5, LS/fx, RT-800 and PSW-650 Last edited by TinCanAlley; 09-28-2013 at 10:52 PM. |
#34
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Got any dud CFL bulbs? They usually have a 10uF 250-450V cap in the base...Though not exactly as likely to be good as a new cap.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#35
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But some scopes can automatically detect the probe setting, and adjust the vertical scale range to reflect the probe attenuation and prevent confusion. This requires both a scope and a probe that support this feature. Do yours?
If your scope is doing this, then the scale really is 5 volts/division. If your scope or your probe doesn't do this for you, then the scale is actually 50 volts/division. This makes all the difference in the world when trying to interpret the waveforms as ripple on a power supply rail. |
Audiokarma |
#36
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I've been thinking about the waveform. It's a 240V source, so the 5V/Div would be too low to show it and the 10x probe would make it 50V/Div and it would cover almost 5 divisions. What I got was way under that. I'm going to use the DMM to go all the way back to the boost diode and when I find the point it's 240V, I'm going to scope it. With a setting of 5V/Div and the probe in 10x, I should get a form that covers over 4 divisions, right?
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#37
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Thanks for the heads up. I have a crap load of new 26 and 13 watt CFLs from China and I don't mind gutting one or two. I'll let you know what I find.
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#38
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Typically, for checking ripple on a power supply, you would operate AC coupled, so you only see the AC component of the signal, and ignore the DC. If you are running DC coupled, the baseline should rise a bit less than 5 divisions (250V) from zero, with ripple superimposed on it. You can do a quick sanity check with a DMM, by measuring the 240V supply twice, both in DCV range (should show ~240V), and in ACV (should show close to zero if no significant ripple is present). From what you are telling us (5 V/div with a 10:1 probe and no auto priobe ranging), the scope is actually showing you 50V per division, or a waveform of ~75 Vpp. This is WAY too much noise on a supply rail, and would easily explain the jailbars. You really need to learn how to use a scope effectively in order to get useful information from it. Take a couple hours and watch this GREAT YouTube training session: http://www.youtube.com/watch?v=8ZKMrzTGxLQ |
#39
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Okay, just did a scope of the 240V line just after it comes off of the resistor into the main feed (where the capacitor is and the where the 240V gets distributed). I had the scope set to AC coupling, V/D set at .5, the T/D set to 20us and probe at 1x. The rippled waveform covered 1.75 divisions peak to peak. So that would make the AC less than a volt, correct?
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Pioneer SX-1080, Pioneer PL-115D, Pioneer CT-F9191, Pioneer RG-1, Wollensak 8050A, Akai 4000DS MkII, Pioneer CS-05 & Polk 1.2TL Denon 5803A, Pioneer DVL-700, Pioneer CT-W603RS, Toshiba HD-A3, D-Link DSM-520, Dish VIP-722, Polk 1.2TL, CSi5, LS/fx, RT-800 and PSW-650 Last edited by TinCanAlley; 09-29-2013 at 12:33 PM. |
#40
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.5 V/div and a 10:1 probe is 5 V/div. A signal 1.75 divisions high would be 1.75 x 5, or 8.75 Vpp.
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Audiokarma |
#41
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Sorry, forgot to mention it was in 1x setting on the probe.
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#42
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...
Last edited by andy; 12-05-2021 at 07:52 PM. |
#43
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I just about drove myself crazy wondering why I could see the ripple of AC on the DC lines, but couldn't see the DC. I thought I had all the settings correct, but still couldn't see a waveform. After realizing I wasn't going to figure it out on my own, I search the net. I figured out how to measure the voltage of DC, but still can't get a waveform. So does the DC on the B+ have a waveform? If so, how do I see it? What would be the settings other than DC coupling? Thanks
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#44
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Ideally, the B+ has no waveform at all, just a flat line of constant DC voltage. Practically, there will always be a small amount of time variation due to incomplete filtering out of the AC source (unless the device is battery powered). Even if the device is battery powered, there can be small variations due to varying load current drawn by the circuits that use the B+ supply.
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#45
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If I see ringing on the base of a transistor, do I look at the collector to see if the ringing has been amplified? Also, I seem to recall someone suggesting I ground the base of the ABL transistor to see if the jail bars go away. The voltage on the base is under 1V, so is it okay to ground it? Doing so won't short anything out?
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Audiokarma |
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