Sanyo VM4209

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.

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:

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:

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:

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 :-)