[R-390] I got my R-390 working!!

[Flowertime01 at wmconnect.com]

Jim,

Some ideas to help with the remaining problems.
You can deal with them one at a time as you want.

New old stock MC KC knobs are @RARE@ but some nice 
reproductions are available. Real work cost real money.
But not like you see on E-Bay. Ask on the R390 mail when you 
are ready to buy a new knob.

The manufacturers tag was missing.

This is normal. The meters were hazard waste. You either pulled the tag and 
sold the receiver as unknown scrape. Or you pulled the meters and sold the 
receiver with no meters and a tag. Most preferred on tag. It come off easy. 
Reproduction tags are about 25  - 30 dollars from Fair radio in Ohio. Again real 
work cost real dollars.

 Xtals in the Xtal oscillator are more energetic than others,  but it's 
nothing I can't live
 with for now.

Again this is normal and do live with in. Think of finding the poorest band 
and then maybe replacing a couple crystals. No assurance the replacement will 
help. Some times its just a leaking trimmer cap in the IF deck. These come 
apart and can be cleaned. But its a real job to do the crystal deck. You may try 
it once in a life time and then do all of them. Just to see if it brings some 
of the weak bands up a bit.

I can turn the Kc knob roughly 10 degrees without any movement of the Veeder 
root.

This is a slip in the zero adjust clutch. The clutch could be dirty. Mostly 
its a zero adjust shaft that does not completely come free of the clutch pins 
and thus lets the clutch slip.

The are several gears between the KC shaft and the Veeder root. Some times 
the right angle bevel gears are not set up closely. This lets you have some lash 
in these gears. This can be adjusted out. Eye ball all the gears to make sure 
some of the anti lash springs are not missing. 

There seems to be a bit of backlash in the tuning.

A good gear train cleaning and lube may be in order. Some of the cams, gears 
and parts can have friction. The anti lash springs are weaker than the 
friction. One end or the gear trains move before the other end moves as the anti lash 
springs get exercised. The KC should move very easily. 

The ALC does not seem to be functioning properly. I can detect no  difference 
between the ALC position and the MGC position. The Function switch is working 
properly. Pin seven of V511 shorts to ground when the position switch is in 
the MGC position (like it should). Perhaps I'm missing something but shouldn't 
the AGC prevent distortion when listening to a very strong signal? It seems to 
me that I shouldn't have to ride the RF gain when the ALC is in.

You may need to pull the IF deck (easy) and the RF deck (hard) and determine 
if your decks have been recapped. We think the R390's had good caps while the 
R390/A were built with some big brown or black plastic caps that have over 
time failed in all sorts of ways.  Some of the R390 also had these bad caps.

The AGC circuit through the IF and RF deck has several of these decoupling 
caps. The caps are away from the AGC jumper on the back panel and have resistors 
in the circuit. So if one of these caps shorts at an IF or RF tube grid, the 
stage acts as if it is always in MGC. The resistance test at the function 
switch or AGC jumper looks good as you get a short and some resistance for MGC and 
AGC. 


The short may not be seen at a tube grid stage because of a resistor between 
the poor cap and the grid. The poor cap may pull several stages some and 
degrade AGC operation.

When you tune a strong station in AGC does the carrier level meter give you a 
strong meter reading. If the meter circuit is not acting well, then you need 
to look between the detector and the meter. Again lots of caps in here to 
provide problems.

When you are ready ask the Fellows here for some help in stepping through the 
AGC functions. The R390 and R390/A are alike. The part number change to 
confuse the bureaucrats but the circuits are essentially the same.

Roger AI4NI   </HTML>