This is an archive of failures which I have experienced and were shared by others VIA the R390A Reflector.   Simply click on the highlighted topics to display the information.  If you have something to contribute, please E-Mail it to me.

Failure was an R390A which had low audio output until the limiter control was turned on.

The failure cause was that C-549, a 300V Sprague "Vitamin Q" had turned leaky about 2 Megohms.  This leakage was swinging the bias on the first audio amplifier, V-601A high causing the degreased audio output.  Because it is passing audio frequencies, I replaced the faulty capacitor with a 600V, .01ufd polypropylene media Orangedrop.

C-549 is easy to find, it's located on a small vertical board on an internal IF shielding partition near the the tube socket of V-507.   It has about 80V on one side and might not be a bad candidate to always replace along with C-553.

I have seen many R390A's which, for some reason, have varying degrees of audio output which I had chalked up to aging.  It may be that this cap is a habitual leaker and had biased off the audio amplifier as above in small amounts.

Talking about sticking slugs in the RF deck?

That is most likely NOT a lubrication problem.  The slugs bind from physical misalignment in the coil forms causing the racks to hang.  You can grease the rack slides until you are blue in the face and perhaps still not fix it.

First, check to see if there is hard grease on the slug rack sides or guide areas, take all that off with some WD 40.  When you have nice clean metal, about 5 drops of Mobil-1 gear oil (NOT GREASE) between the side of the RF deck and movable slide will insure its free movement.

If the above does not correct the problem, here is how to proceed and fix the slug binding:

Locate which slug is sticking.  Using the tuning and band change controls, cause that slug rack supporting to drop and insert the slug as far into the coil form that it will go.  Take a #1 Phillips screwdriver and carefully loosen the two screws holding the slug bracket to the slug rack and let the slug/spring center the bracket so the slug is free in the coil form.  Tighten the bracket screws being careful NOT to allow the bracket to move on the slug rack.

Again, using the tuning and/or band change controls, cause the offending rack to move and see if it still binds.  Repeat the above as necessary on that or other racks which might be binding up.

DO NOT under ANY circumstances lubricate the actual powdered iron core with anything but a dry lubricant such as talcum powder.  Depending on the slug coating/binder, the oil in the grease can leach into the core and change its density, attack the coil form, etc.....    As soon as the receiver gets more dirt into it (And it will, ever see a totally clean R390(A) RF deck??) it will stick to the grease and the binding in the form will be back, this time in a whole new
dimension.

It also makes an incredible MESS.

With regard to GREASE, I end up using just a very tiny amount on any R390A restoration and only on slow moving parts like the antenna trimmer worm gear.  Most lubricating is done with 90W oil.

-Chuck Rippel-

A quick analysis showed the output of the first xtal oscillator as measured at P-221 to be approximately 3/4 volt P-P  instead of the usual 5.2V P-P or so.  Additionally, when performing the variable IF alignment, T-207 would only show a peak at the very bottom of the
slug travel.

The problem turned out to be C-327, located across the primary of T-207 had changed value.  Once replaced, the proper injection levels to the mixer were restored.

-Chuck Rippel-

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My R-390A,Stewart Warner S/N1831 had very week reception below 8Mhz, signals were 20+ DB down. It turns out the mixer, V202s 17Mhz oscillator input level I measured early on, was way too low for proper operation. The reading was less than a volt P-P instead of the later 16 volts P-P after the repair.

C327 in the 1st oscillator circuit was bad. T207 would peak but with the very low output. I have found many other mica caps in B+ circuits of 74A4, and 51J4 receivers to be the problem also. With this trouble shooting I got to know this receiver. It is a fine machine and a joy working with the MILL SPEC parts. I hope my experience will help others in repair of their R-390A.

73, RON K1VYU          WESTBOOK CT USA

They also have split aluminum and stainless steel clamp type split shaft collars from 1/8" to 1" bore.  Price ranges from $3 to $15.  Only available with hex screws, though.

Haven't had to buy either one yet.  They will send you a catalog for the asking and it is filled with lots of neat stuff.

73 de Richard, KB5WLH

ABEN
P. O. Box 4118
Jersey City, NJ 07304

e-mail: AviDov@aol.com

If you can't find the pot or are unsure how to install it, Drop me an E-Mail. I keep them at hand and can supply you with a kit including the pot, new shunt resistor and wiring diagram for $20 + postage.

-Chuck Rippel-

You don't need the dedicated and expensive UG-979/U connector to connect an antenna to the BALANCED input.  Here is an easy way to configure the jack properly, gain maximum receiver sensitivity and avoid the use of some expensive, hard to find connectors in the bargain:

Facing the REAR of the receiver, connect the center conductor of a piece of RG-58 to the RIGHT hand pin jack of the BALANCED INPUT.  Attach a spade lug to the shield and connect it to the stainless steel screw directly to the upper right of the BALANCED input.

Using a small piece of wire, insert it in the LEFT hand pin jack of the BALANCED input and GROUND the other end to the stainless steel screw located directly to the lower left of the BALANCED input.

You can put a connector on the other end of the RG-58 or terminate it as appropriate.

-Chuck Rippel-

Note:  See pictures and a further explanation of this circuit by clicking here.

Dave Metz posted the failure conditions and cure for a very common R390A problem, failure of HR-202.  HR-202 is an approx 1-1/4" diameter, cylindrical oven containing crystals Y-203 and Y-201.  It plugs in an octal socket located at the far right hand corner of the R390A RF deck.  There is a removable spring clip affair across the top to assure that HR-202 stays in place.  Having any of the two crystals within HR-202 fail can cause a lot of head scratching.
Finding complete HR-202 assys becoming more difficult so rebuilding a defective one is the preferred option.

The first crystal within the HR-202 assy is Y-203, the 200KC crystal for the calibrator.  This crystal can fail completely causing the calibrator to not operate.  More commonly, it will have drifted with age and be out of range of the calibrator adjustment, C-310. Zero beat will not be achievable against the alignment standard being used.  The calibrator zero adjustment, C-310 is accessible through the back panel.

The cure is to replace Y-203, the 200KC crystal within HR-202.

The second crystal in HR-202 is Y-201, the 17 mHz 1st xtal oscillator.  It drives V-207 whose plate is transformer coupled VIA T-207 to cathode of the first mixer, V-202.  Part of the alignment procedure involves peaking T-207 during the IF alignment.

A Y-201 or associated circuit failure will cause all bands below 8 mHz to be "dead."  It is THE most common cause of that symptom. Signals from .5 to 7.999 mHz go through the first mixer, V-202 and its tracking IF network consisting of Z213-1 through Z213-3. The oscillator, V-207 is turned on by the application of screen voltage, 150V B+ through S-208 (rear) which is sourced from V-605, the OA2 voltage regulator.

The cure, as Dave correctly noted, is to replace Y-201, the 17mHz crystal.

Note:  The T-207 peak is very broad and its alignment will NOT cure a "dead" receiver.

It has occurred to me that part of a very complete R390A restoration might include replacement of ALL the crystals.  This not only includes the calibrator and 1st crystal oscillator as above but also the dozen or so crystals in the 2nd crystal oscillator associated
with V-401.

In nearly every R390A, these xtals have drifted in frequency.  A quick test is to simply zero beat the calibrator on one band then start changing bands and note the zero beat error from band to band.

However, the cost of the crystals alone would be impressive to say the least.  However, they are available from International Crystal.

1. No carrier meter indication at all. Dead needle on all signals.
2. Boomy, distorted audio. Obviously no AGC action. Audio returns to perfect if rf gain is turned way down, either in AGC or MGC.
3. Measured voltage between AGC jumper and ground with 70 db signals is +2.5 vdc! Doesn't vary much with varying signal or in AGC or MGC. No negative bias at all. (This compares to my "healthy state" big signal AGC voltage at the jumper of about -8 to -11 VDC. I know 'cause I
measured weeks back.)

Here is the "fix:"

I replaced C519, a .005 disk ceramic AGC bypass to the grid of the 3rd IF with a .0047 Orange Drop. While I was at it, I also replaced C521, a 200V 0.1 tubular with a 400V 0.1 tubular I had on hand.

Radio works great now. Everything back to normal. Have over -9 V at the AGC jumper when on a strong station and pin 6 on the big plug/jack on the IF deck (the AGC line) now tests to infinity, as the TM says it should. (It was 53K!)

-Dan Martin-

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I had an AGC problem that got me scratching my head several years ago. It was on an older Collins unit, 1954 vintage I think. Ended up changing out C226,C255,C273,C284,C286,C297, and C319 plus about half the resistors. ALL the caps showed *some* leakage, but only under voltage.

Another 390A had C255 leaky and was dragging down the AGC just enough to be a problem.

-Tom Norris-

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Another AGC failure showed up where strong signals overloaded the receiver.  Checking at the rear panel ACG jumper, I found that a signal reading over "20" on the Carrier Meter would only output -4 volts of AGC v/s the spec of about 7.  This would cause the receiver to overload.  Obviously, something was leaking AGC voltage to ground.

Referring to the manual, It can be seen that disconnecting the rear panel jumper and testing to ground with an ohm meter will isolate the leak to the voltage generating/time constant circuits or where the ACG is applied.  In this case, the meter showed 830K to ground on the bus feeding AGC voltage to the IF amplifiers.

By isolating the various circuits, it was found that the leakage was in one of the filters.  Further isolation revealed that the 4kc filter was leaking to ground.

The failure was corrected by replacing the 4KC mechanical filter.

Here is the limiter mod I was looking for, and so here is the relay requested by some of you.  Credit KD0HG and Electric Radio #70.

Symptom: The limiter adds audio distortion even at its lowest setting.

Solution:  Install a 33K  1/2 W resistor in series with R527 (390A) or R539 (R390).

The limiter can now be used up to 1/2 the pot's range with no noticeable distortion.

If you wish to try before buying, simply remove the jumper on the diode load screws at the back of the set, and replace it with the 33K resistor.  This trial will demonstrate the mod without going inside the rig.

-Tom Marcott-

The levels are quite high for direct coupling of the DIODE LOAD directly into an amplifier.  Plus, you don't want the additional connection to load down the diode point.  Even with the
390's fairly tight AGC, a change in signal upwards will overload the amplifier until the AGC clamps the change.  Plus, there is about 8.7 volts DC on the diode load jumper.

I made a simple network of a 1/2W, 470K resistor in series with a 10ufd, non polarized capacitor and put it in series with the DIODE LOAD bus and the center conductor of the audio phono cable going to the AUX input of my amplifier.  Works great!  The resistor lowers the
audio level and the 10ufd cap blocks the DC voltage on the diode load bus while still being able to couple well into the lower audio frequency regions.  While zero beating a station using the BFO, I could see the speaker move at about 5 hz.

A further improvement would be to use a metal film resistor (1/2 Watt) and a larger value non-polarized cap.  Polystyrene would be nice if you could find on that high in capacity.

-Paul Courson-

Note:  See a further explanation and pictures of this circuit by clicking here.

-George Rybicki-

One cause of intermittent snapping and popping heard in the audio can be traced to leaking filter capacitors C603 and C606.  These are multi-section electrolytics of 3 X 30UFD at 300V and 2 X 45UFD at 300V.  Also, the as there are sections of the capacitor dedicated to the audio section, audio quality can also be improved by replacing them.

Remember, due to their using a acidic electrolyte, electrolytic capacitors fail with time rather than use.  They can be reliably rebuilt and repotted using new internal components.  Click here for rebuilding information.

-Chuck Rippel-
 

-Chuck Rippel-

Also-

Problem:  Low Audio, Distorted Audio, or No audio.  When Local Gain is advanced to 9-10,audio is barely perceptable.  Audio returns to normal when the Limiter is turned on.  This problem exhibits similar symptoms of other posted Limiter
problems. This problem appeared on an EAC/Hammarlund R-390A while operating.

Discussion: C532, 100pf (connected from Pins 6 and 7 of V507 to ground) is used to supress any remaining IF elements in the signal while allowing audio frequencies to pass into the Limiter circuit.  This capacitor had failed in a resistive state under operating conditions (read open with an ohmmeter). The additional load of this capacitor on the Plate/Grid of V507
(B section) caused the voltage at the Plate/Grid to be only about 22 voltsas compared to the nominal 78 volts as shown in the technical manual. This causes V507B to cutoff.  When the Limiter was turned on, the plate voltage was sufficient to allow conduction due to the re-biasing of the tube in the Limiter-On state.

Solution:  Replace C532 with a 100pf 1KV disc ceramic.  Note, this capacitor is located against the bottom of the chassis at the base of V507's socket and is very hard to get to.

73, Randy, N4TVC -

Page prepared by R. Charles Rippel

Revision: December 24, 2001
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