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From: Jeff Liebermann <jeffl@cruzio.com>
Newsgroups: sci.electronics.repair
Subject: Re: Altec Lansing ATP3 Speaker system transformer failed.
Date: Sun, 28 Apr 2024 19:57:51 -0700
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On Sun, 28 Apr 2024 16:08:57 -0700, Bob F <bobnospam@gmail.com> wrote:

>This speaker system I used on my main computer died yesterday - no power 
>at all.
>
>I traced the problem to the transformer, a 12.5V 2.5 A TP57U25F from Ten 
>Pad Industrial.

Check your typing.  The company is Ten Pao.
<https://www.google.com/search?q=ten+pao+transformer>
There is usually a part number on their transformers.  Find the number
and 

>Testing the transformer coils, neither the 117V input or 
>the 12.5 V secondary show conductivity - they are both open circuit. The 
>fuse for the primary circuit was not blown.

Conductivity?  Plug it in and measure the AC voltage produced at the
output of the transformer.  

>My question here is, if both coils are open circuit, does this suggest 
>that a major short on the PC board got the transformer too hot so it 
>tripped temp circuit cutoffs in both coils, so it is unlikely that 
>replacing or fixing the transformer will fix the speaker? Or, is this 
>kind of failure common for such transformers?

I've seen opens on commodity power transformers are when there is
mechanical or chemical damage to the wires.  More common are the
thermal fuses hidden under the tape covering the transformer windings.

>If I wanted to try a different transformer to test the board, what 
>should I want the transformers open circuit voltage to read on my 
>Greenlee DM-20 DVM.  Should that be 12.5V? I do have a variable voltage 
>variac I could use to adjust a slightly higher voltage transformer down 
>to 12.5 or whatever should be needed.

I can't answer that without knowning something about the type of power
supply.  Is the bridge full wave, full wave center tapped, or
something else?  Is the 12.5 V before or after the voltage regulator? 
Digging with Google:
<https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-audio-equipment/58859-system-dead-atp3-altec-lansing-computer-speak-system-with-subwoofer>
Looks like you're not the only one with a transformer problem in the
ATP3.  At least we now have the part number, but for the 230 VAC
version:
  TEN PAO Model no.:TG51219F0
  Input: AC 230V/50Hz
  Output: AC 12.5V/2.5A
I can't figure out the 117VAC version part number.





"Hacking an Altec-Lansing ATP3 Subwoofer for Stand-Alone Operation"
<http://www.kk4ice.com/?p=570>
This doesn't answer your question, but might be useful reading. Please
note the external on-off switch wiring.  One a different model speaker
system, I had a similar "no power" failure that was caused by me
kicking the sub-woofer enclosure and eventually breaking the on-off
switch.



-- 
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558