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Altec 1592B Mixer Amplifier Rebuild, Pt. 2: Power Amplifier Main Board

In the last post, I had started the rebuild of the main, aka Power Amplifier board, on the Altec 1592B. Now it's finished.

Here's the top view.

You can see the pink (!) Takman REX resistors. I replaced all of the old signal resistors with these. The important power supply resistors (those going to transistor collectors) were replaced with Takman REY metal films (those are blue).

Here's the pcb from a different angle. The bypass caps were replaced with Nichicon FGs, and the signal caps are now Elna Silmic IIs.

Now on to the tone control board.

The board is held on with the low frequency (LF) and high frequency (HF) pots.

First we take the control knobs off.

Then undo the 1/2 inch nuts holding the pots on.

This is the easy part.

With the pots undone, the pcb drops away from the front panel.

There are eight soldered connection at the bottom - the connection are on two 4-pin plastic connectors you can see at the bottom of the board.

I taped each group of wires together and labelled them before desoldering them from the connectors.

I also made a diagram of the wire colors and connections.

I do this all the time for anything like this that has to be disconnected. I have legal pads on the workbench filled with nothing but these diagrams! Sometimes I look at them and think "what the heck is this?"! Now I title them so I know what the diagram is for.

Here's where using solder wick to desolder is invaluable. These are fairly delicate connections and I want to get them off cleanly.

Here's the left side after desoldering. The wires kept their shape, so it will be easy to slip them back over the connectors and solder them after the board is ready to be reinstalled.

See the melted insulation where the iron touched it on the black and brown leads? I was a bit clumsy in those tight quarters and paid more attention on the other side. This won't affect anything, it just annoys me.

After the board is disconnected, I put in the pc board stand.

But all is not well. The heat from the iron made one of the connector pins come loose from the connector.

Fortunately, it's an easy fix.  I squeezed the pin down into the connector block with pliers and heated it with the iron at the same time, and it went right back down. And it has continuity, so score one for me.

(I couldn't hold the iron and the camera at the same time, so you have to imagine the iron heating the pin.  It was either the iron or the camera and I chose the camera).

Next we'll rebuild this board and then the main chassis.

Altec 1592B Rebuild Project
Part 1: Overview and Initial Dissassembly
Part 2: Power Amplifier/Main Board (This page)
Part 3: Tone Control Board
Part 4: Filter Capacitor Replacement
Part 5: Reassembly


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