Salas DCG3 preamp (line & headphone)

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Russellc

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Joined 2003
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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
 
Salas

Salas

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Joined 2002
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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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Russellc

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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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Russellc

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Think I found the problem....how I mixed this up I have no idea. The two transistors on the far left and far right, are marked IRF9610. How I mixed these up with the other two I don't know. Hopefully I didn't mess them up. Too tired to switch out now. Generally I would be up to the wee hours changing them out, but that is how I probably did this in the first place.

Russellc
 
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dewdrop

Member
Joined 2004
Russellc said:
Think I found the problem....how I mixed this up I have no idea. The two transistors on the far left and far right, are marked IRF9610. How I mixed these up with the other two I don't know. Hopefully I didn't mess them up. Too tired to switch out now. Generally I would be up to the wee hours changing them out, but that is how I probably did this in the first place.

Russellc
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Congratulations, at least you have identified the issue.
 
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Russellc

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Problem even sillier than I thought. Checking all my transistors not yet installed I have the two M3 DN2540 pieces, But no IRF9610! I have two Q3 MJE15030G, and I have two Q1 MJE15031G.

This means I put all 4 IRF9610 devices on the power supply board in the heat sinked positions. Why the + positions voltages are correct, I do not know! Is this even possible?

Now to remove all 4, (assuming the are all IRF9610) and replace with proper Q1 and Q3 transistors. If the two positive transistors are correct, then there must have been a mixup when the parts were being put into kits. I think the smart money is on me installing all four of the IRF 9610s on the power supply board in the place where Q3 and Q1 should have been.

Is it even possible the IRF9610 would work in the - section of the power supply? (In the Q1 position?)

Russellc
 
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