Sunn Beta Lead - Resistor melted out - Can't figure out problem

[johnskoolie]

Hey everyone, I am new to this forum. I posted to the general questions and someone redirected me to this section.

Original link: https://music-electronics-forum.com/...t-other-issues

I'd love to get this amp up and running. Thanks!

[loudthud]

Here is a link to a thread with the Beta series Service Manual: https://forum.sunnstillshines.online...36807#msg36807

From your description, I think you are talking about the +/- 15V regulators on the power amp board. This is the most common failure in the Beta series amps. The two transistors, Q1 and Q11 in the circuit really need heatsinks, they run pretty hot even when the amp is working correctly. One of them is probably shorted.

[johnskoolie]

Could you explain to me what "+/- 15v regulators" are please? Also, this morning I pulled Q1, Q11, C9, C10, C2, C3 (pieces right next to Q1 and Q11) and tested them all - no issues. Now I really don't know what to do.

[x-pro]

(Could you explain to me what "+/- 15v regulators" are please?)
This is the link "Original link: https://music-electronics-forum.com/...t-other-issues" in post # 3 the Tassieviking explains it.

[loudthud]

Could you explain to me what "+/- 15v regulators" are please?

See the Beta Power Amp Block Diagram on page 2 of the Service Manual that I linked above.

[johnskoolie]

See the Beta Power Amp Block Diagram on page 2 of the Service Manual that I linked above.

I have it and I'm trying to look at it but I don't really know what that means in terms of actually checking places. What do I put my multimeter on? I have a bunch of parts out of the board that I checked and they are all good. Should I put them all back in?

[x-pro]

Could you explain to me what "+/- 15v regulators" are please? ...... Now I really don't know what to do.

You may be good at something else.
But this is not a simple device. It's not a flashlight on a light bulb.
Take it to a specialist for repair.

[johnskoolie]

You may be good at something else.
But this is not a simple device. It's not a flashlight on a light bulb.
Take it to a specialist for repair.

I don't have the money for that to be honest. I have a 6month old and blowing money on another amp is just not possible right now. My goal is to learn from people willing to share their knowledge and get this amp working. I'm motivated and willing to read whatever, I just need some help getting the info.

[johnskoolie]

You may be good at something else.
But this is not a simple device. It's not a flashlight on a light bulb.
Take it to a specialist for repair.

I think its terminology that is confusing me. I checked the TIP30 transistor if thats what they mean by +-15v regulator

[x-pro]

They are properly called a voltage stabilizer: +15V & -15V

[x-pro]

1. Disconnect the speaker and check its resistance.
2. Turn on the amplifier (without the speaker!). Do not supply anything to the input of the amplifier. All controls on the front panel to the minimum position. Check the main supply voltages. This is +40V and -40V relative to the chassis. Then check the power supply of the preamp +15V and -15V. If you don't know how to measure bipolar power supply correctly, read the Internet or books.
3. Check the output DC voltage - this is the output of the amplifier. If the amplifier is in good working order, it should be 0.

[DrGonz78]

Just out curiosity how many components did you remove from board? Each one represents a newly introduced variable to diagnosing the failure in the amp circuit.

[x-pro]

...how many components did you remove from board? ..

No spare parts?
Then you shouldn't even turn it on!

[Helmholtz]

There are no regulator chips here.
+15V is regulated by Q1/CR1 and -15V by Q11/CR5 on the power amp board.

[DrGonz78]

Are there two threads open on this one amp? I mean come on man. Like Biden always clammers come on man!