[Coco] CoCo 2 repair - Transformer?

[Chad H]

Actually I was going to consider that as an option "IF" I ever found a good service manual for the 26-3027/3127 models.  I know the unit needs both 12V/5V power supplies but I don't know if 12V+/5V+ is sufficient or if there are required 12V-, 5V-, etc. rails.  Heck I don't even know where I would even tie into the main board such a external power supply.   If I did, and it was a simple 12V+/5V+/GND source I would tack on a molex connector and hook in a Pico ATX power supply :)

-----Original Message-----
From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Louis Ciotti
Sent: Tuesday, December 23, 2014 7:25 PM
To: CoCoList for Color Computer Enthusiasts
Subject: Re: [Coco] CoCo 2 repair - Transformer?

Why are you looking at replacing the transformer, From your last posts it sould like you found the problem with a bad ground lead. If I were looking at doing anything with the CoCo power supply I would do a total gut and replace.  Been a while since I looked at it, but I seem to remember that it was not exactly the best power supply design, even for the time it was produced.

On Tue, Dec 23, 2014 at 8:11 PM, Michael Graham <mkgraham at gmx.com> wrote:

> 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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