[Coco] CoCo 2 repair - Transformer?

[Chad H]

10-4 on the first part.  I went back and looked at parallel secondary with single primary as it seems to be that type.

Not sure about the 17.5v part, I just tested that with my spare 26-3136 for comparison and here's what I found....

Keep in mind these tests were done at the secondary output connectors directly without a load..

26-3136:

---------- 17.6vac -------

--  8.74 -------   8.74 --

T  ------    C    ------  T

*********************************

26-3127:

---------- 21.3vac -------

--  10.6 -------   10.6 --

T  ------    C    ------  T


There is definitely a difference.  Either it's differently rated supplies, or one is out of specification.  I could not find a 17.5vac power supply on Digikey, but they do have series 16V and series 18V which would be close to the 26-3136 readings.  They have series 20v which would be close to what I showed for the 26-3127.   Wish I could find a 26-3027/3127 manual that would show the specs for that supply but it doesn't seem to exist.  Also I'm not sure what the tolerances are on the board's power circuit.  If I were to replace the transformer, hypothetically, I would try to find one with the closes output voltage to what it's previous supply was putting out to be safe as possible.

-----Original Message-----
From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Michael Graham
Sent: Tuesday, December 23, 2014 7:11 PM
To: CoCoList for Color Computer Enthusiasts
Subject: Re: [Coco] CoCo 2 repair - Transformer?

Hi!

I think you're looking at the specs on the transformer in the wrong way.  You're measuring 10.8V on each side of the tap, but that wouldn't make it a 10.8V transformer, that would make it a 21.6V transformer.

It probably is actually a 17.5V center-tapped transformer, but you're measuring 10.8V instead of 8.75V on either side of the tap because the CoCo isn't drawing the full amount of current for which the transformer is rated.

--Michael


On 12/23/2014 6:52 PM, Chad H wrote:
> In trying to identify potential replacement sources for power supply 
> parts I've yet to pin down one for the power transformer in my primary 
> CoCo 2.  It seems to be the same one in the 26-3027 as in the 26-3127 
> but there is no label on the transformer itself.  The technical 
> reference I found for the
> 26-3136 talks about a 17.5vac transformer but when I measured my 
> 26-3027 secondaries I got approximately 10.8vac on each point to 
> center.  I tested with the unit on and with it off, not much 
> difference.  I was wondering if the following might be a possible candidate.
>
>   
>
> http://tinyurl.com/lcwp2hp
>
>   
>
>   
>
>    Can someone tell me if I'm on the right track?  Thanks!
>
>   
>
> -          Chad
>
>


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