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<!DOCTYPE html>
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<title>fritzm.github.io - Sanyo VM4209</title>
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<h1>Sanyo VM4209</h1>
Sun 13 March 2022
by <a class="url fn" href="https://fritzm.github.io/author/fritz-mueller.html">Fritz Mueller</a>
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<div><p>Some time back I purchased a Sanyo VM4209 B&W video monitor on eBay. Sold as working, it arrived with
apparently working horizontal but no vertical deflection. The price had been right, however, so it was just
shelved into the repair queue.</p>
<p><br><img style="display:block; margin-left:auto; margin-right:auto" src="/images/micros/vm4209.png" title="VM4209 video monitor"/><br></p>
<p>I now have a few DEC VT series terminals to work on and would like to have a small video monitor available on
the bench for this, so I pulled down the VM4209 to give it a look. Given the lack of vertical deflection, the
first thing to check would be the vertical deflection power transistors, Q105 and Q106 here:</p>
<p><br><img style="display:block; margin-left:auto; margin-right:auto" src="/images/micros/vm4209-vert-schem.png" title="VM4209 vertical deflection"/><br></p>
<p>It turns out these transistors are quite well buried in the guts of the monitor on a small aluminum heat sink.
Took a while to work my way in to them, and required unsoldering a few leads and removing the CRT:</p>
<p><img src='/images/micros/vm4209-crt_thumbnail_tall.jpeg' title='VM4209: CRT' onclick='pswipe("micros",0);'/>
<img src='/images/micros/vm4209-chassis_thumbnail_tall.jpeg' title='VM4209: chassis with CRT removed' onclick='pswipe("micros",1);'/>
<img src='/images/micros/vm4209-bottom_thumbnail_tall.jpeg' title='VM4209: underside of main board' onclick='pswipe("micros",2);'/>
<img src='/images/micros/vm4209-vtrans_thumbnail_tall.jpeg' title='VM4209: vertical deflection heat sink, with Q106 replacement' onclick='pswipe("micros",3);'/></p>
<p>Sure enough, the lead connecting Q106 collector to ground had been broken, and the part tested bad. Q105
appeared healthy, and there were no other apparent signs of distress in the surrounding circuitry. Q106 is an
out of production 2SB474 germanium PNP in the less common TO66 package; I opted to replace it with the
"modern" equivalent NTE226. Re-assembled, and was greeted immediately with a functioning raster. Pulled out
an Apple II Plus to test with:</p>
<p><img src='/images/micros/vm4209-appleii_thumbnail_tall.jpeg' title='VM4209: repaired, with Apple II Plus' onclick='pswipe("micros",4);'/></p>
<p>This was quite fun for a short while, until a RIFA cap in the Apple II power supply let go, filling the dining
room with acrid smoke. So, expect an additional article on that one in the near future :-)</p></div>
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