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Re: A-4 Repair [message #26539 is a reply to message #26502]

Fri, 09 February 2018 15:39

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Is the cap on the output 1uF or a 0.1uF? Typical Zobel networks will use 0.1uf and a 22 ohm resistor. Have you tried the amp with a different speaker?

To measure the voltages, set your meter to read dc voltage. The highest voltage that you will see is about 45 volts, so set your meter to the range that will cover that amount of voltage.

Set the amp up on a well lighted bench top and plug the amp into the wall socket and turn it on. If you have a light bulb limiter use it for now. Connect the black lead of your voltmeter to the metal chassis. Carefully touch the red meter lead to the different points in the circuit and see what voltages you get compared to the voltages listed on the schematic.

For example, the two large filter caps each have two screw terminal on the top of the cans. Touch the red lead to where the red wires connect to the cap and read the voltage. You should get about +45 volts dc. Next check where the green wires connect to the other filter cap, you should read -45 volts dc.

The readings that you get will not match the schematic exactly, but what you look for is something that is completely wrong. Be very careful when probing, because if you accidentally short two points together with the tip of your meter lead, you can cause problems, like shorted transistors, etc.

Watch out for the 4 metal heat sinked transistors on the power amp pc board, because the metal cases are connected to the circuit and have high voltages on them.

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[Message index]

		A-4 Repair By: Jonomega3 on Sat, 27 January 2018 08:20
		Re: A-4 Repair By: chicagobill on Sat, 27 January 2018 12:26
		Re: A-4 Repair By: Jonomega3 on Sun, 28 January 2018 00:28
		Re: A-4 Repair By: chicagobill on Sun, 28 January 2018 14:13
		Re: A-4 Repair By: Jonomega3 on Sun, 28 January 2018 15:44
		Re: A-4 Repair By: stevem on Mon, 29 January 2018 08:18
		Re: A-4 Repair By: Jonomega3 on Mon, 29 January 2018 21:16
		Re: A-4 Repair By: chicagobill on Mon, 29 January 2018 23:48
		Re: A-4 Repair By: stevem on Tue, 30 January 2018 12:07
		Re: A-4 Repair By: Jonomega3 on Tue, 30 January 2018 13:24
		Re: A-4 Repair By: stevem on Tue, 30 January 2018 15:24
		Re: A-4 Repair By: Jonomega3 on Wed, 31 January 2018 12:47
		Re: A-4 Repair By: stevem on Thu, 01 February 2018 08:23
		Re: A-4 Repair By: Jonomega3 on Thu, 01 February 2018 11:13
		Re: A-4 Repair By: Jonomega3 on Thu, 08 February 2018 15:12
		Re: A-4 Repair By: stevem on Fri, 09 February 2018 08:32
		Re: A-4 Repair By: Jonomega3 on Fri, 09 February 2018 12:54
		Re: A-4 Repair By: chicagobill on Fri, 09 February 2018 15:39
		Re: A-4 Repair By: Jonomega3 on Fri, 09 February 2018 17:07
		Re: A-4 Repair By: Jonomega3 on Fri, 09 February 2018 18:30
		Re: A-4 Repair By: chicagobill on Fri, 09 February 2018 23:46
		Re: A-4 Repair By: Jonomega3 on Sat, 10 February 2018 12:00
		Re: A-4 Repair By: chicagobill on Sat, 10 February 2018 23:54
		Re: A-4 Repair By: Jonomega3 on Sun, 11 February 2018 00:27
		Re: A-4 Repair By: stevem on Sun, 11 February 2018 06:24
		Re: A-4 Repair By: Jonomega3 on Sun, 11 February 2018 10:58
		Re: A-4 Repair By: chicagobill on Sun, 11 February 2018 15:41
		Re: A-4 Repair By: Jonomega3 on Sun, 11 February 2018 21:05
		Re: A-4 Repair By: Jonomega3 on Mon, 12 February 2018 10:10
		Re: A-4 Repair By: stevem on Mon, 12 February 2018 07:29
		Re: A-4 Repair By: Jonomega3 on Mon, 12 February 2018 09:04
		Re: A-4 Repair By: stevem on Mon, 12 February 2018 10:18
		Re: A-4 Repair By: Jonomega3 on Mon, 12 February 2018 10:41
		Re: A-4 Repair By: chicagobill on Mon, 12 February 2018 12:47
		Re: A-4 Repair By: Jonomega3 on Mon, 12 February 2018 13:25
		Re: A-4 Repair By: chicagobill on Mon, 12 February 2018 14:25
		Re: A-4 Repair By: Jonomega3 on Mon, 12 February 2018 16:07
		Re: A-4 Repair By: chicagobill on Mon, 12 February 2018 18:08
		Re: A-4 Repair By: stevem on Tue, 13 February 2018 07:39
		Re: A-4 Repair By: Jonomega3 on Tue, 13 February 2018 11:04
		Re: A-4 Repair By: chicagobill on Tue, 13 February 2018 16:40
		Re: A-4 Repair By: Jonomega3 on Thu, 26 July 2018 12:43
		Re: A-4 Repair By: chicagobill on Fri, 27 July 2018 00:02
		Re: A-4 Repair By: Jonomega3 on Sat, 28 July 2018 14:31
		Re: A-4 Repair By: stevem on Sun, 29 July 2018 06:06
		Re: A-4 Repair By: Jonomega3 on Sun, 29 July 2018 14:10
		Re: A-4 Repair By: Jonomega3 on Thu, 16 August 2018 11:45
		Re: A-4 Repair By: stevem on Thu, 16 August 2018 12:40
		Re: A-4 Repair By: Jonomega3 on Thu, 16 August 2018 13:14
		Re: A-4 Repair By: Jonomega3 on Thu, 16 August 2018 18:51
		Re: A-4 Repair By: stevem on Fri, 17 August 2018 06:51
		Re: A-4 Repair By: Jonomega3 on Fri, 17 August 2018 06:58
		Re: A-4 Repair By: stevem on Sun, 19 August 2018 06:15
		Re: A-4 Repair By: Jonomega3 on Mon, 20 August 2018 12:18
		Re: A-4 Repair By: stevem on Mon, 20 August 2018 12:27
		Re: A-4 Repair By: Jonomega3 on Fri, 24 August 2018 18:22
		Re: A-4 Repair By: chicagobill on Sat, 25 August 2018 00:15
		Re: A-4 Repair By: Jonomega3 on Sat, 25 August 2018 07:58
		Re: A-4 Repair By: Jonomega3 on Sat, 25 August 2018 11:43
		Re: A-4 Repair By: chicagobill on Sat, 25 August 2018 12:41

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