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Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 24th November 2018, 05:42 PM   #3261
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by Russellc View Post
Oh, RY/J resistors are 1 ohm also if that info is needed.

Russellc
Yes, we checked that. See if the mV drop across R2 indicates about 5mA (ILeds=mVR2/33Ω). If yes, it means no problem in J2 or in the targeted Led bar VF.
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Old 24th November 2018, 06:04 PM   #3262
Russellc is online now Russellc  United States
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Ok, all my resistors are in correct location. I have made a chart to label all the transistors and there correct position. If no problem there will proceed with tests you specify.

Question: If led strips light up fine, can they still be damaged? Is it possible If I reversed positions of J2 and Q4 to have this effect?

Let me ascertain correct positions and I will return with your measurements. I have disconnected the power to examine board.

One more question: To test power up, I joined All the red primary leads together and all the black primary leads on both transformers. These two bundles were each attached to terminal block and power cord to that. Power cord then plugged into variac.

Hope this isnt something stupid...

Russellc
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Old 24th November 2018, 06:17 PM   #3263
Salas is offline Salas  Greece
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No they can't be damaged if they light up fine, especially when they look as bright and in same hue as in the positive reg sides that output correct voltages.

The primary wires should be alright. Else you would not have expected secondary AC voltages.
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Old 24th November 2018, 06:19 PM   #3264
Hikari1 is offline Hikari1  United States
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Pretty easy to accidentally put a bc550 instead of bc560 in the negative rail. Iam 40 years old and can barely read the type on those small bipolars. Did you check that?
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Old 24th November 2018, 06:31 PM   #3265
Russellc is online now Russellc  United States
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Getting ready to. I got about 22 years on you! @Salas, I just measured across R2 and got 150mV.....maybe I swapped the two small pieces...I hope.

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Old 24th November 2018, 06:33 PM   #3266
Russellc is online now Russellc  United States
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G-r-r-r-r-r-r...oh well. Lets have a look at the tiny bits.

Russellc
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Old 24th November 2018, 06:37 PM   #3267
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150mV/33Ω=4.54mA i.e. pretty close to our 5mA Led bars feed rough target. Thus your J2 CCS & Leds Vref system works fine
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Old 24th November 2018, 06:50 PM   #3268
Russellc is online now Russellc  United States
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Well thats good, does that mean I dont have a J2-Q4 mix up? I guess I better check the heat sinked devices for proper positioning? If they were in wrong place, then + side would have to be messed up. What's left, deadQ3? How could I have killed both? Hate to install new ones just to kill them. This board is just sitting on top of a styrofoam box to fire it for test...can't imagine that would make difference over being on standoffs in chassis...

Next advice? order new Q3 devices? any Q3 killers I should check for?

Thanks, glad at least led and J2 are good. Is it possible J2 switched with Q4 and still R2 measurement correct? I will double check positioning.

Thanks in advance,

Russellc
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Old 24th November 2018, 07:00 PM   #3269
Hikari1 is offline Hikari1  United States
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You need to make sure q3/q4 are the correct devices and oriented correctly. If correct, test vbe like Salas said (just turn over the boards and test from pins on bottom). Vbe indicates the transistor is working...
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Old 24th November 2018, 07:01 PM   #3270
Salas is offline Salas  Greece
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It's not possible you put a BC-560C instead of a PF5102 in J2 position and you got CCS not to mention reading proper mA. Static can kill semis sometimes.
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