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Metallion

Schematics for kustom Lead Amp top?

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Looking for Schematics for a Kustom Lead III guitar Amplifier top

The out signal to the Speaker doesn't work.
Line seems ok.

The repair shop cant find any schematics from the maker, and they cant do anything more until they have schematics.
Voltage varies from 0.5 to 20 V without explanation.

Have looked on the net but found no Kustom schematics specifically for the III Lead top.

Anyone got them as PDF or knows where to find them?

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Looks like I got the right plans, for some "pc506..." board.

Now it's about + 0.7 V DC out, for the speaker out port.
He says that value is ok, But it varies, and he can't figure out why.

When he cools the two "Differential steps", (called Q1 and Q2: "2122" or 4249?) one gets to plus + 2-3V, the other to minus - 2-3V.
It's some kind of balancing coupling.
The repairman cant figure out if it should be a difference on the two steps like that.
, if he should keep looking for a fault or stop there, since what should happen in the amp, with it's values etc, is not clear.
If someone knew?

He gets a 25V + DC at times
It's a -71-78 make amplifier module

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Is it the Kustom PC5065? There's a link to it here (third post down). It also has steady-state voltage measurements  marked on it.

 

19 hours ago, Metallion said:

When he cools the two "Differential steps", (called Q1 and Q2: "2122" or 4249?) one gets to plus + 2-3V, the other to minus - 2-3V.
It's some kind of balancing coupling.
The repairman cant figure out if it should be a difference on the two steps like that.

Where is this measurement being taken from? The two transistors configured in that way is what's called a long tail pair. Under normal circumstances they will behave equally and oppositely as you describe. Ie, if one transistor is driven to push its output  voltage down, the other will want to pull its voltage up.

 

On 9/4/2017 at 2:24 AM, Metallion said:

Voltage varies from 0.5 to 20 V without explanation.

It's possible that the output is merely following the change occurring at the input. If the voltage at the input changes, then you're going to see a matching (bigger) change at the output as well. If cooling the input transistors results in an unexpected voltage change at the output, then I'd be focusing on checking if Q1 or Q2 have become thermally unstable. I'd also be looking at any nearby components that may have an impact on the stability of Q1 and Q2. Capacitors can go leaky with age, so C2, C3, C7 and C8 would be prime suspects too.

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