<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta name=Generator content="Microsoft Word 15 (filtered medium)"><!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Aptos;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
font-size:12.0pt;
font-family:"Aptos",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
p.xmsonormal, li.xmsonormal, div.xmsonormal
{mso-style-name:x_msonormal;
margin:0cm;
font-size:12.0pt;
font-family:"Calibri",sans-serif;}
span.EmailStyle22
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;
mso-ligatures:none;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 90.0pt 72.0pt 90.0pt;}
div.WordSection1
{page:WordSection1;}
--></style></head><body lang=FR-CA link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span lang=EN-CA style='font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'>No. The transformer is soldered on a PCB so no way to change the primaries polarities.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=FR style='font-size:11.0pt;font-family:"Calibri",sans-serif'>De :</span></b><span lang=FR style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Mike Bryant <mbryant@futurehorizons.com> <br><b>Envoyé :</b> 19 février 2026 21:07<br><b>À :</b> synth-diy@synth-diy.org; jpdesroc@oricom.ca<br><b>Objet :</b> Re: [sdiy] Questioning on why both of this power transformer primary windings went almost short..<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal><span style='color:black'>Pure guess but has somebody already replaced the transformer once, and has JUST ONE of the primary windings reversed ? This would mean they would fight one another, and with larger fuses happily overheat and melt the insulation of the windings.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p></div><div class=MsoNormal align=center style='text-align:center'><hr size=2 width="98%" align=center></div><div id=divRplyFwdMsg><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:black'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:black'> Synth-diy <<a href="mailto:synth-diy-bounces@synth-diy.org">synth-diy-bounces@synth-diy.org</a>> on behalf of Jean-Pierre Desrochers via Synth-diy <<a href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a>><br><b>Sent:</b> 20 February 2026 01:20<br><b>To:</b> <a href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a> <<a href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a>><br><b>Subject:</b> [sdiy] Questioning on why both of this power transformer primary windings went almost short..</span> <o:p></o:p></p><div><p class=MsoNormal> <o:p></o:p></p></div></div><div><div><p class=xmsonormal><span lang=EN-CA>A customer brought me a guitar preamp that he said ‘blows its internal fuses..’</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>I checked the internals and found that both of the internal 315mA primary windings fuses were blown (F2 & F3).</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>The main 500mA fuse (F1) was ok.</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>So I connected my variac to <u>only one</u> of the primary windings (no fuses) to find that<br>reaching around 90VAC it started to drain around 1 AMP !</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>I checked the other primary winding alone and it behaved exactly the same,</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>1AMP at around 90VAC.</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>These measures were done with none of the secondaries connected (free wires).</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA> </span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>So my questioning is what the heck almost shorted each of these primary windings<br>exactly the same way..?</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>I connected external AC voltages to each of the secondaries bridge (one at the time)<br>and there were no shorts on each of them. The resulting DC voltages were as expected.</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>To create those shorts at each primaries it would have needed<br>that the 315mA fuses would have been replaced by much higher values<br>with some kind of shorts somewhere in the secondaries side.. ?</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>OR this is a manufacturing default that waited to awake ?</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>Anyway I ordered a new transformer replacement, but I don’t want<br>to fry it again because of something else that blew the first one..</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA> </span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA>What do you think ?</span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA> </span><o:p></o:p></p><p class=xmsonormal><span lang=EN-CA> </span><o:p></o:p></p><p class=xmsonormal><img border=0 width=802 height=301 style='width:8.3541in;height:3.1354in' id="x_Image_x0020_1" src="cid:image001.jpg@01DCA24D.C8871630"><o:p></o:p></p></div></div></div></body></html>