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Old 07-09-2010, 12:39 AM
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Leader LCG-400 NTSC Pattern Generator

I picked this up cheap recently. The packing job was ridiculous - 6 or 7 tightly nested boxes. Kinda like a "blooming onion".


I've never used one before, but it looks like a very cool device.


Unfortunately, I detected the nasty stink of burnt electronics shortly after powering it up. I popped it open and discovered a fried tantalum capacitor.
So far gone I can't read the value





Anyone know what the correct value is for C824 in one of these ? The one right next to it is 4.7uF @ 25v so I figure that's a good guess.

-
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Last edited by bandersen; 07-19-2010 at 08:53 PM.
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Old 07-09-2010, 11:12 AM
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I've got one of these here at work. It's been sitting on the junk pile out in the garage for a while now. I'll grab it and check the value of the cap for ya.
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Old 07-09-2010, 11:18 AM
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You are correct. Both caps are 4.7 @ 25.
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Old 07-09-2010, 11:41 AM
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Thanks! I popped a new one in and no luck
I do have a clean +5 VDC going to all the logic ICs and the clock oscillator is running, but I'm not finding any signal beyond the stuff right around the clock.

When you say it's sitting on the junk pile, do you mean it's going to be thrown out ?
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Old 07-09-2010, 01:23 PM
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Quote:
Originally Posted by bandersen View Post
When you say it's sitting on the junk pile, do you mean it's going to be thrown out ?
No we hung onto it as a rainy day project. It's full of bad caps. I'll look around and see if I can find the service manual. If I find it I'll copy the schematic for ya.
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Old 07-09-2010, 01:29 PM
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Thanks!
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Old 07-11-2010, 11:10 PM
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IIRC, Leader used ICP's as fuses in some of their instruments. I've got a Leader Audio Generator and FM-Multiplex unit that both use ICPs. I was surprised to see them - ICP-N35 in one unit, not sure what the ultiplex unit uses. Hitachi also uses them in their Oscopes - my V1050 has two.

You might check to see if you have a bad ICP - it looks like a two legged plastic transistor and will only have the suffix marked on it. Other than tha, check for your analog voltages - +/- 12 or 15 Volts typically.

Leader makes great stuff - Stereo manufacturers required Leader equipment in their warranty stations - that's how I got mine, form a closed Panasonic/Technics dealer. You'll also like the availability of parts - others put custom stuff in their equipment, but leader used standard stuff, unlike Tek and HP.

CHeers,
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Old 07-12-2010, 02:42 PM
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Thanks for the advice. I just picked up the service manual today and will start checking out the power supply first. I suspect that shorted out capacitor took out something else like an ICP.
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Old 07-13-2010, 01:19 AM
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I've got pretty much 0 on the +15 and -15 volt rails. I disconnected all the leads to the power supply and it rose up to +/- 15.
I threw 250 mA dummy loads on the PS board and it's putting out a clean +/- 15 volts. Nuts Now I have to go digging through the other boards!
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Last edited by bandersen; 07-13-2010 at 01:31 AM.
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Old 07-13-2010, 10:31 PM
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While testing the boards, I had two more tantalum caps pop So out they all have to go - all 81 of them
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Old 07-14-2010, 10:08 PM
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If you go back with Tantalums, up the voltage rating, and go with Kemet brand caps - the only ones I've found to be consistently reliable. 50V tants are cheaper these days - used to be big bucks for tantalums above 35 Volts or 22uF.

If you go with electrolytics, go with a low-ESR, low impedance cap - Nichicon PJ series (Mouser has 'em) have worked well for me in Tek O'scopes. 4.7uF @ 50V will set you back about a quarter each. 81? ...only 16 cents each.

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Old 07-14-2010, 10:17 PM
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You know, looking at your pix of the innards, it looks a lot like my Kikusui equipment - right down to the zero ohm jumpers and markings. I wonder if Kikusui and Leader were ever one in the same? If so, you'll find it easy to work with and troubleshoot.

Heck, even the knob (Variable Composite output) looks like my Kikusui O'scopes position knobs!

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Old 07-14-2010, 10:56 PM
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Thanks for the tips - I ordered some Kemet brand tantalums from Mouser. I hope to have them by the weekend.

It's certainly easy to work with. Few, if any, proprietary parts, and it's all clearly labeled. Also, it uses single sided boards.
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Old 07-19-2010, 09:02 PM
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I finally finished replacing all those nasty tantalum caps and it works



A few of the patterns are off a little, but the calibration procedures show how to fix them up. The circle should be centered better in this case.




This is what the optional multi-burst module puts out. I'm guessing it's used to test bandwidth ?


These is an RF output on ch 5/6 in addition to the composite output but it seems a little weak. There's another version that does channels 3/4 which I'd rather have. We still have a local analog broadcast on channel 6 that interferes with the test pattern if I go through the antenna terminals. Perhaps I'd be better off feeding the composite into a Blonder Tongue modulator and then into the set

Here it is on an Admiral chassis tuned to channel 5. Now, I can clearly see that the horizontal linearity is way off



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Old 07-21-2010, 12:21 AM
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That's a nice generator. More bells & whistles than my Leader LCG-396.

That multi-burst pattern looks similar to the "multiburst bar sweep" pattern from my Sencore VA62A, which just came up in the color forum. I hadn't tried that before (the VA62A is sick), but here's what the manual says about the pattern:

"The multiburst bar sweep pattern is used for troubleshooting or aligning the luminance circuits in a TV receiver or VCR. The pattern's main use is to isolate video problems related to frequency response. This pattern also provides a reliable method to align the video IF stages of a receiver for the best video frequency response with minimum picture distortion."

Just flipping around other sections, the manual also describes how to use that pattern when adjusting traps, setting purity & convergence, setting the color oscillator, adjusting color killer, probably more.

The pattern looks similar to yours, but not identical.

Phil
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