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Subject: Re: +8/-6.5 PSU Replacement

From: "Mike" <mborish_2000@...>
Date: 2011-03-28

Here's what you need to do:

1.) Don't worry about the ground.

2.) Take pictures of the thing before you take it apart. Make sure that all component orientation is legible and that you can identify all of the components with their respective places.

3.) As a general rule, avoid NTE subs.

4.) Take note that the whole thing is interconnected. +15 and -15 are referenced in the +8.5 and -6.5 If a +15 or -15 is down, your PSU won't work.

5.) Make sure that you use jumpers for the sense circuits if you are powering up the PSU unloaded.

6.) Pull out Tr710, Tr711, Tr712, Tr714 and D712 - use the multimeter diode test to determine if they are not dead. Check Diode D715 with the power on because it is a Zener; it should read about 15 volts across the anode and cathode. Also check D713; it should read about 6v (guess) when everything else is working.

7.) Replace the OP AMP

8.) Check to make sure that the fuses have continuity.

9.) Check the 1k resistors that are going from the Emitters of TR711 and TR712 to ground. Check the .47 ohm resistors from Tr709 to Tr714.

10.) Check Tr709 and Tr714 like you did with the small signal transistors. These are located on a different panel of the PSU under the fuses in the middle and can be easily overlooked.


If you need help crossing the transistors, or have any questions, let me know.

-Mike





--- In yamahacs80@yahoogroups.com, "B. Cooper Sloan" <mistercooper@...> wrote:
>
> I wish I were certain, ramcur was kind enough to send me an assortment of
> pulls to swap out, I feel like I must have already replaced most of the
> transistors and diodes, I suppose its possible one got zapped in the
> process. I'm poking about with my meter now.
>
> Cooper
>
>
> [Non-text portions of this message have been removed]
>