[R-390] R-390A IF Module Layout

[Craig C. Heaton]

Capacitors Part 2

I use a Dremel tool to work on several of the caps. The two cans on the power supple module; I cut the rolled edge off of the cans. Then use a small torch to heat the cans to loosen the black uckumpucky and pull the guts out of the cans. New electrolytic caps go inside. 

The bathtub cap on the inside of the back panel; once again use the Dremel tool with a cutoff wheel, on the bottom slit three sides and open like a sardine can. Insert a new electrolytic cap. Bend the flap back in place, add a dab or two of solder on the corners. 

The "cap that rots" on the audio board is a wet tantalum, expensive! A solid dry tantalum is cheaper, works good, lasts long time. Mouser has them and orange drops,etc. 

The 2uF oil paper cap on the IF module, no PCB's. Once again the NTE will either fit inside or on the bottom of the chassis. Dremel tool once again to cut the square metal can open and stuff in a new cap. 

The R-390/A (s) that I've rebuilt: BBOD's were shot! On my Sprague TO-6A capacitor analyzer, BBOD's tested bad for value & insulation resistance. Electrolytic caps were leaky! 

I try to use the R-390/A (s) just about every day, and they work.

Caps that will drive you crazy! The silver micas have given me the most problems. The cap analyzer shows they are good, but circuit doesn't work. Resistors are close to listed values, tubes are fine, replaced with new tubes, circuit still doesn't work. In this case, check the parts list and if there is a silver mica in there, shotgun it. Replace everyone in that circuit.

Places where silver micas have failed me: RF cans, when peaking the RF cans and the slug adjustment peaks just before the slug falls out of the rack, good chance one or more of the silver micas are bad in that coil assemble. Note the amount of signal needed to peak that rack compared to the other racks. If the RF cans are in good conditions, each rack should use just about the same amount of drive from the signal generator.

And last, a couple months ago the silver micas in the 200KC crystal calibrator drove me up the wall. Had to replace all of them, a couple of resistors, and the darned Amelco wanted the 200KC crystal from my Motorola..#$^%^&^& The Motorola was happy with any 200KC crystal.  


Are we having fun yet?

wd8kdg
Craig

 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Richard W. Solomon
Sent: Thursday, December 11, 2008 5:26 PM
To: r-390 at mailman.qth.net
Subject: [R-390] R-390A IF Module Layout

Is there available a picture or pictograph showing the component
layout (position) of the under-side of the IF Module ?
After getting mine out I see that it is infested with BBOD's.

It would help me make a list of Orange Drops I need to order.

Side note: Too bad the Audiophools have latched on to OD's.
The price on e-Pay is absurd and assortments (at a reasonable
price) are hard to come by.

73, Dick, W1KSZ
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