R390A PTO tracking and alignment

[W4AMV]

Hello Forum.
Progressing on a R390A restoration. The receiver functions on all bands with poor sensitivity on some bands below 8 Mhz, 50 uV or better for 10dB S/N and better than 5 uV above 8 MHz. Obviously all in all, poor. Per the volumes of literature on the WWW and the excellent material by Chuck Ripple and others, I am convinced that care needs exercised prior to jumping into an electrical alignment prior to mechanical. One of the key alignments is PTO tracking. I have checked this on some bands and it is spot on over the 1 MHz span and not so great on others! For example, on the 7 MHz band, the zero clutch or zero frequency adjust will not provide for proper frequency readout. Its off by 13-15 KHz. This despite the PTO is dead on on other bands below 8 MHz and the 1 MHz span is spot on. How can this be? Am I missing a gear plate or mechanical tracking somewhere cause the 17 MHz xtal LO cannot be perfect on one band and in error on another??
Thanks in advance, 73, Alan

[WD8KDG]

Alan,

The AM forum is a great reference.....but here are three things to do/read.
http://mailman.qth.net/pipermail/r-390/
http://www.r-390a.net/
........and of course the one and only famous Y2K manual now in Rev.3

The first link will take you to the e-mail reflector and at the top of the page is a link on how to sign on.
The second link is a couple years of reading, check out References and near the bottom of that page is Wei-Li's "Pearls".
In Pearls there is a section of e-mails for every thing possible about an R-390/A.

There is a method and steps to restore one of these great receivers.

#1: Get rid of BBOD's
#2: Old electrolitics gotta go,gotta go
#3: Do 1 &2 before ever plugging it into a wall outlet
#4: All of the mechanical alignment must be spot on or the electrical will suck wind!
#5: Then proceed to the electrical alignment.
#6: Fun part starts here, finding the bugs.

So have you dropped the front panel and made sure the cams are at the correct locations with the veeder root counter set at 7 +000.

Poor sensitivity under 8 MC is a classic symptom of the 17MC crystal failing, location top right rear corner in little round metal can. Both crystals in that can were meant to run at 75 degrees C. There is another 17MC crystal in the crystal deck, swap them and see if that helps. Either crystal will work in either location, but only one was meant to handle the heat at 75 degrees C. If you want a stable RX pay attention!

Craig,

PS: Strongly suggest posting questions on the e-mail reflector, the guys & gals there are tops.

[nq5t]

One of the key alignments is PTO tracking. I have checked this on some bands and it is spot on over the 1 MHz span and not so great on others! For example, on the 7 MHz band, the zero clutch or zero frequency adjust will not provide for proper frequency readout. Its off by 13-15 KHz. This despite the PTO is dead on on other bands below 8 MHz and the 1 MHz span is spot on. How can this be? Am I missing a gear plate or mechanical tracking somewhere cause the 17 MHz xtal LO cannot be perfect on one band and in error on another??

A couple possibilities.

1.  The PTO interface to the Veeder Root readout needs adjustment
2.  One (or more) of the heterodyne oscillator crystals (on the crystal oscillator sub-chassis) have drifted in frequency (and need to be replaced)

The PTO tuning spread, linearity, and accuracy is independent of band or the physical adjustment of the RF deck (other than the interface to the counter).  If the PTO covers a 1Mhz spread accurately on any band, it will cover it accurately on all bands (subject to the items I listed).  Obviously, if the RF deck mechanism is out of adjustment, other things won't work right, but it does not affect frequency accuracy.

You may be able to tweak the counter linkage to get the zero adjustment range to work sufficiently on all bands.  But if you are off as far as you indicate on some, I'd suggest checking the heterodyne crystal oscillator frequencies to the receiver specs, and replace any crystals that are off.  ICM can provide exact replacements at a reasonable (depending on your point of view — about $25 each) cost.

Grant NQ5T

[W4AMV]

Thanks Craig and Grant for some key clues. I totally forgot that the error in the PTO tracking below 8 MHz on some bands and not on other bands (also below 8 MHz) could be traced to the SECOND LO FREQUNCY ERROR! It would also explain if the 2nd LO injection level were way off, the huge variation in sensitivity on the bands below 8 MHz. For example 5 MHz at 10uV and 7 MHz at over 100 uV. The 1st LO, 17 MHz is running as I measued its injection level, but I should check its frequency for completeness. I am holding off on dropping the front panel and pulling the RF deck until I realize I must. I checked the cam alignments on the ones I can see at 7+000 MHz and they are dead on with the alignment marks. I have the Y2k rev 3 and the videos from Chuck. Huge volumes of information and more is welcome. I think part of the problem is seeing the forest through the trees!

[flintstone mop]

The 1st xtal oscillator is in trouble. The reason your R390A is a little deaf below 8mhz. There are 3 xtal oscillators in the R390A. The radio is broken down to three major bands, the reason for 3 xtal oscillaotrs. Slight possibility that it is the tube. More likely circuit trouble under the RF deck. I hope you have the manual. There are nice clear procedures who to dismantle the radio to get to these sub-chassis. And turn off the xtal heaters. No need for that to operate. There was some info from Chuck Ripple why he recommended to turn them off.
Fred

[W7NGA]

The R-390A receiver was one of the best projects I've taken on. Many reasons for poor sensitivity, but when noted on a particular range of frequencies check the slugs for that range on the RF deck. My slugs kept breaking off the shafts and falling to the bottom of the can. Easily fixed ...

dan W7NGA
San Juan Island, Wa.

[W4AMV]

Problem found, at least this one. The answer on this one is the 2nd LO. Example on 7 MHz, the second LO desired is 21 MHz and obtained from the 2nd harmonic of the 10.5 MHz xtal. The observed injection level as well as frequency is significantly in error. This explains not only the inability to check the run of the PTO but the horrible sensitivity. In retrospect, this one is obvious. As a word of caution, those who desire to check their PTO run, to see if it is to short or to long, please check this on a band where you know in advance that the 2nd LO is spot on! Next, I need to determine if the xtal is bad or the plate tune circuit for that band is defective. As the 2nd xtal oscillator output operates either fundamental, 2nd or 3rd harmonic.

Again, thanks in advance, Alan

[flintstone mop]

Yeeow I discovered how rusty my brain was on the R390A. The radio is basically triple conversion from .5 to 8mhz and double conversion 8-32 mhz.
I don't know where I was going "with the radio broken down into three bands and the separate oscillator blabber." Sorry 'bout that!
I was trying to find any notes on troubleshooting the AGC. I had two IF modules with the same AGC problem and they were repaired by ME several years ago. I do not want to mention the so-called R390A guru on the East Coast who told me that, the one IF module I sent to him, was in perfect condition.
It turned out to be a shotgun affect. Visually looked for, and replaced any friggin cap that was attached to the AGC line. Went through the RF deck, everywhere. The problem turned out to be the IF module both times.
Alan I hope that you have a happy radio now.
Fred

[W4AMV]

Hi Fred. Thanks.

No, the radio is not happy yet but it's on the mend. I did some more trouble shooting today trying to rule out what is broken from what is actually operating decent. For example, on the 15 meter band, 21 MHz, the radio is hot. I mean I can readily hear .15 uV. Of course this is a relative number since I am using the balanced port (120 ohms) driven from a 50 ohm generator. But thats ok, it tells me alot about the goodness of the back end, AGC, audio subchassis portions of the 2nd and 3rd IF etc... For sure the 40 meter band is not dead due to the lack of a 17 MHz oscillator but due to a 9 MHz 2nd oscillator subchassis and failure to provide sufficient 3rd harmonic injection. Of course it gets more interesting, since the same xtal is used on the 15 and 24 MHz band and they are not quite as dead!! But dead enough to be problematic. When the 2nd LO is humming and operating correct, I see 6-7 volts peak to peak RF at the 2nd LO connector, while less than 2 V p-p is clearly what I see when the senstivity is way off. Could be dirty bandswitch , etc... But bottom line, panel will need to be dropped and the LO subchassis removed for repair. Thanks for the feedback !