[R-390] Some trouble shooting thoughts

[Perry Sandeen]

List,
There have been several posts asking for help with trouble shooting so here are a few tips of mine.
1.  The modern digital VOM's have a high enough impedance for trouble shooting.  The requirement for a VTVM came at a time when they were analog causing a noticeable voltage drop on high impedance circuits.
2.  R390's are not a tinker toy receiver.  They require some investment in test equipment to be able to service them.
A. Everyone should have a spare set of good new or used spare tubes. This because tube tester are usually a fortune if one can find the. Tubes are a high failure rate item

B. I find the most helpful tool is a O'scope. I have a Tek 2445 that I bought at a hamfest for $180 ten or so years ago. There are a gizzilion scope models available. Tek scopes seem to be the best quality and are often found at hamfests for reasonable prices. All one needs is a 2 channel 50 MHz bandwidth. Usually more common are the 100MHz bandwidth units.

Looking on Epay one can find Tek 22XX series for $200 delivered.  Large choices of used probes are available as well.
C.  Get  large (2 ft by 3 ft) print out of "The almost ultimate R390A upgrade schematic" parts one and 2.  There is a ton of practical advice from a number of Guru's to help you. It is large enough for one to take notes (in pencil) of your various reading.  Some people just print out a specific section on there home printers.  This works well.  Some have used a laptop to go through the ski's. I personally don't think this is a good idea. You can't annotate your readings.
D. Good RF signal generators are big, heavy and still fairly expensive. It's hard to invest in one if you have only one or two radios.  BUT there is a $30 signal source that's usually advertised in QST magazine that plugs into the antenna input and provides some calibrated signals.  (I couldn't find the ad in my QST - maybe a list member can help)
HTH
Perry KM6FQV