I have a Precision 642 tube tester that is completely dead. I am Getting juice to the tester from the line cord,fuse is good, changed all resistors and capacitors,no pilot light, checked all wiring. The only thing left is the transformer, and don't known how to check it. What do you think?<P>------------------<BR>

Hi Joey<P> Check continuity of the AC input circuit. An ohm meter will help you find what is open.<P> If the transformer burned out you should be able to tell by smell.. <P>------------------<BR>Norm

The Transformer looks in good shape, does not smell burnt and the 5Y3 tube is O.K.<P>------------------<BR>

Does the 5Y3 filament light? Can you trace the AC line wires? They might go through a line adjust control. If so be sure it's turned up. Sometime line adjust pots are electrically open on one end. This acts as an on-off switch.<P>------------------<BR>Norm

Do you have a schematic? I have a 612 also and the schematic and can help walk you through it perhaps. Go through Norm's ideas first of course.<P>------------------<BR>

If "642" is a typo and you do,indeeed, have a 612,then most of the resistors are used only in the battery test function.<BR>When you have a classic open circuit like this,don't waste time replacing components in a "shotgun" servicing approach.<BR>Determine that continuity exists on the primary side of the trannny,and if it does,there is then a simple matter of tracing the juice coming from the secondary and finding the spot at which it no longer flows from point "a" to point "b".In an open series circuit,maximum possible voltage drop appears across the open component itself.<BR>Only a few things can cause an open;poor solder joint,incorrect wiring,poor switch contact,poor internal contact in one of the controls,open resistor,open coil in pot,rheostat,.etc.<BR>When is the last time this tester was refurbished and recalibrated?It may be time for a complete "physical" on this old workhorse,anyway.<BR>Malcolm<P>------------------<BR>

Hi, It was the line control pot. Does anyone known where I can get one. the schematic reads 300 ohms, but no wattage. Thanks Joey.<P>------------------<BR>

Hi Joey<P> Probably need a 25 watt rated pot. Here is a list to look through if your eyes don't wear out first. There are 2000 items. <BR> <A HREF="http://www.oldradioparts.com/2a22fil.txt" TARGET=_blank>http://www.oldradioparts.com/2a22fil.txt</A> <P> Some of us may have a replacement but have to check first....<P>------------------<BR>Norm