Installing (but not operating) the Nomad Radio PLL Synthesizer in the Browning Golden Eagle Mark IV (but NOT the IV-A) Transmitter Copyright 2004-2005

Preliminary Version 0.1 November 1, 2005

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All contents copyright @2004-2005

If you are here, it's for a fairly short set of possible reasons. We'll skip the "What, it's not an automatic rifle?" crowd.  We'll assume that you are here because you would really like to actually use the transmitter in Browning Laboratories' next-to-last base-station model.

The channel selector that Browning used for a 23-channel transmitter was always a rotary switch with a halo of 23 separate quartz crystals, one for each transmitter channel.  Browning had already decided to do away with this arrangment while designing a successor product to "top" its wildly successful "Golden Eagle Mark III" two-piece base station radio.

Everyone else in the CB base-station business had abandoned the "two-piece" (separate transmitter and receiver cabinet) layout, selling one-piece "transceiver" radios.  For whatever reasons they had, Browning Laboratories Inc, of Laconia, New Hampshire stuck with the two-piece design, but the transmitter would use a state-of-the-art technique called the "Phase Locked Loop" (PLL) to slice one quartz crystal up into 23 separate transmit frequencies. Never mind that it took literally dozens of 14,16 and 24-legged, power-hungry, primitive digital integrated circuits to replace those other 22 quartz crystals.  Never mind that they were still learning to use this new technology, if it's DIGITAL, it must be better, right?

The 23-channel Golden Eagle Mark III SSB transmitter contained a total of 29 crystals.... and not one "logic chip". When it was designed in 1970 (more or less), integrated-circuit (chip) technology had barely been invented.  By the time five years had passed, and the next model was being readied to produce, chip technology had exploded, and the design  techniques to use them were just being worked out.

And there's the rub. Browning was a little ahead of the curve, and produced a literal nightmare of complexity and borderline performance, not to mention rotten reliablity.

Ever ask yourself what a knob marked "Reset" is doing on the front of a tube-type transmitter? I see it as the factory's way of admitting "We screwed up, and put this thing on the market before it was ready for prime time"
The original selector and pll
If they had designed the Mark IV's electronic channel selector and PLL the right way to start, that knob would have been completely unnecessary.  The folks at Browning Labs Inc. of Laconia, New Hampshire recognized their error, and followed up with the Mark IV-A soon after. This time they got it right. They chose a Motorola "one-chip" pll for the frequency synthesizer half, and a "one-chip" computer made by Texas Instruments for the electronic channel selector/display. Of course, neither of those chips were available in the early 70's when the original Mark IV was being designed. 

When it became clear to us that there was no way to make either the factory channel selector or the factory 'tin-can' PLL perform well enough to suit our customers, we borrowed the basic layout of the Mark IV-A channel selector/pll and began producing a complete replacement for both.  Here is the standard installation package, which includes  the new selector control, display and PLL boards. The electrolytic capacitors are to improve the odds of a satisfactory final result.

This unit replaces both the pair of circuit boards that mounted behind the front panel, AND the 'tin-can' PLL that was mounted behind the panel meter . This leaves a gaping hole in the chassis behind the meter, but that should improve the air flow. Also, the power consumption for the selector/pll is reduced radically, which also cuts the temperature rise inside the transmitter cabinet.

The spring-return, center-off "Up/Down" switch is replaced by a rotary encoder, 36 clicks per turn. One 'click' moves the transmitter frequency 5 khz, only one-half channel. At two clicks per whole channel, it takes just over two full turns of the channel knob to cover 40 channels.  The green LED to the right of the digits is used to indicate that your channel frequency is one-half channel higher than the channel number displayed. When the green LED is dark, you are on the channel number displayed.

The yellow LED on the left is used to indicate that you have turned the selector to the left  of channel 1, and the number displayed is below channel 1.
Nine below

The first step before installing one of these is to make the radio transmit BEFORE tearing anything loose from it. If the transmitter is broken BECAUSE the pll has failed, the digits will be dark (or flickering), and the relay in the back of the transmitter will not 'click' when you key the mike.  FIRST, we need to defeat the "out-of-lock" detector that prevents the transmitter relay from keying.

If there are other issues in the transmitter that prevent it from showing output power, now is the time to sort those out. Tearing out the old synthesizer and installing our replacement is a lot of work. You'll be pretty unhappy if it STILL won't transmit after all that effort. Much better to get it to show some output power before going to all that work. 

The suicidal white nylon "Molex" plug

Even before we get to making the transmitter show some power, there's the issue of the transmitter  connector at the rear of the receiver.

 If yours looks like this, stop right here.

Either remove the white nylon plug and socket, wiring the two units DIRECTLY together, or convert it to the larger, black "Jones" style connector used in the later versions of the radio.  This connector is NOT up to the job. It will fail and cause all manner of grief if you don't get rid of it. 

As if this weren't enough, there's another "GOTCHA" to check for before you get any deeper into this procedure. 

If R229 has been visibly overheated or burned, there's a 99-percent chance that your mode switch has failed. Replacing the synthesizer won't fix this. At all. You will have no end of trouble from a failed mode switch. Once the brown bakelite insulation breaks down on that switch, it just gets worse. And worse. 

That switch just gets more expensive every time someone offers it for sale. And replacing it is one big headache, too. "Jumping" the connections to run AM mode only is possible, but there are no instructions for that procedure. Not yet, anyway.

The next preliminary step is to bypass the "lockout" switch on the transmitter relay. If your transmitter is already working, and shows good power/audio, you STILL need to do this. We WON'T be hooking up the "out-of-lock" transistor Q304.

The pic below shows the yellow wire that feeds power to the relay coil.

Remove the yellow wire from this trace, and move it to the one with the "+" next to it. This trace is the junction of D301 and C320, the separate 6-Volt supply the feeds the relay coil.

You might as well clip that pesky orange wire close to the solder trace, too.  It will be coming loose soon, anyway.

This would be a very good time to replace C320 with the 2200 uf 10-Volt capacitor. The old C320 might be okay, but a new one will last longer.

Of course, what you should do now, is to hook up the mike, dummy load and power. The relay will now click when you key the mike. If the pll is still running at all, you should get at least some power on the wattmeter when you key the mike on AM. If you have a frequency counter in the coax line, the frequency may well be way above 40 or below channel 1. That's not so important. What matters is that you should see some power out of the transmitter now, even if the channel LEDs are still dark.

If the factory PLL is totally dead, you won't see any transmit power, even when the relay clicks. Doesn't mean that it will ALSO be dead with the new synthesizer, but it raises the uncertainty.

Now comes the really messy, distressing part: Removing the stock channel selector boards, channel switch, pll module, and a rat's-nest of wires.

For starters, unplug the BNC plug at the top of the PLL shield can. For now, just move it aside. Clip all the wires that attach to the tie strips between the two 5-Volt regulator chips. These are at the rear-most end of the PLL shield can.

Remove the two flat-head countersunk #4-40 screws that hold the channel display board to the top edge of the front panel. Save them, and the flat washers found between each small bracket and the upper rail of the front panel.

Remove the large main tuning knob (1/16-in. allen wrench). Remove the (1/2-in. wrench) bushing nut that holds the switch to the front panel.

You will need to clip two or three ground wires from the lower edge of the channel display board to swing it away from the front panel.  Some of the wires lead from the selector board into a grommet in the chassis deck. Follow these wires underneath to the "Reset/LED" switch. Cut all 6 wires on that switch. Cut the wires on the "Scan Rate" control.

The colors of some of these wires may vary. Clip the FAR end of each wire  leading away from the Channel Selector boards to the rest of the transmitter.

Remove the two #4-40 (1/4-in size) nuts that hold the rear end of the PLL shield can to the rear edge of the chassis.

 Once enough wires are clipped, the PLL shield will slide out if you lift the rear and rock it a little side-to-side.

This should leave you with two wires coming up from below the chassis next to the relay. Push them down below the chassis, and turn the transmitter over.

The white wire with the red stripe leads to the mike socket. Pull the wire out of the bundle, and then push it into the grommet directly beneath the channel digits, long enough to reach the top edge of the front panel. Clip i t to that length, and strip 3/8" of the insulation from the end.

The plain white wire leads to a tie strip near the old PLL at the rear of the chassis underneath. Pull the white wire out of the wire bundle, and clip it  few inches from the tie point where it meets the violet wire from inside the fat receiver cable.

Behind the front panel just below (above?) the Spot switch is the other end of that RG-58 coax with the BNC plug on the other end.

Clip the coax, leaving enough to remind you where the new coax will attach a little later.

Now  you can extract the coax, pulling it out of the wire bundle from above the deck.

The next step is to drill two holes in the top edge of the front panel.  They will each be direcly above the "High" and "Low" limit LED holes in the front panel. You should be able to 'sight' a centerline onto the front panel's top edge one directly above each LED hole in the front panel.  The perspective of the photo distorts this, but trust me. The parallel lines are each one directly above the LED hole on each side of the digit window.

Shows one centerline above each "limit" LED hole

Unless you have a "Whitney" punch or similar hole-punch tool, you should use a spring-loaded center punch to keep your drill bit from wandering from the cross hairs where the hole should be.

Next, remove the two right-angle brackets from the original channel-selector board. You don't need the original screws or nuts.

Remove the old mount brackets from the original channel-selector board.

Each bracket is mounted to one top-front screw on the new channel-selector board.

The short end of the bracket points to the rear.

Each hole should be countersunk slightly. This will prevent the heads of the mount screws from sticking up too far. A 3/8-inch drill bit works about right. Just don't overdo it and enlarge the bottom of the hole.

If you plan to use the stock "776" mike, you will need a source of power. If so, strip and solder the red/white wire from the mike jack here.

If you won't be using a '776' mike that needs power fed to it, you can remove the white wire with the red stripe, where it attaches just to the rear of the mike socket.

Remove the nut from the rotary encoder, so that the lockwasher is between the new channel selector and the front panel. Be nice to the wires on this control, they are easy to bung up. Uhhh. Big Note here. When I say "easy" to bung up, that means EASY. The wires will place leverage against the three tiny metal pins on the encoder. If the solder that connects the pin to the encoder comes loose, you'll have a selector that turns ONLY up or ONLY down, usually. Keeping this leverage force to a minimum while you're handling it will prevent this. The pin connections on the encoder are devilishly hard to repair if they go bad.

Now you can mount the new rotary encoder in the front panel. Be gentle to the wires. They will have the least stress on them if they "point" to one side coming out of the encoder when it's fastened to the panel. Use care threading the nut onto the plastic bushing, it's easy to cross-thread accidentally. The flat face on either side of the bushing makes it much easier to cross-thread than it does to get the nut STRAIGHT. If it doesn't feel right, back off and try again. Plastic threads are TERRIBLY easy to bung up with a metal nut.

When you put the large selector knob back onto this plastic shaft, it helps to line up the setscrew with the flat face on the shaft. The knob will rest straighter on the shaft, and won't be as likely to loosen up in use.

Now mount the synthesizer to the front panel with the flat-head #4-40 screws provided. First, line up the green and yellow LEDs with the holes in the front panel, before lining up the screw holes in the brackets.

The white coax and the long, white power lead both go into the chassis hole directly beneath the new synthesizer. The black wire gets grounded to the tie strip just below the "On the Air" light.

On the underside, the new output coax goes where the old one did. Remove the cut off ends from the old coax under V301. You can solder the shield on the new output coax directly to the ground trace as shown here. It's teflon. The soldering heat won't melt the coax. The center conductor should be soldered where the old center conductor was. Do that first, and then solder the shield to the ground trace.

The one remaining wire you haven't connected is the long white teflon wire. This is a touchy subject, since this is the one way you could completely destroy the whole project. Hook that power lead to the wrong spot, and POOF! It goes up in smoke. And it won't be MY fault. Trouble is, this unit was designed to be installed here, in my shop under my supervision. So far none of my trained techs has screwed up this detail. Not once. I wasn't thinking ahead far enough to include reverse-polarity or over-voltage protection circuits. And there's no room to add them onto this design. Sure would be a good idea for the "KIT" version, but for now you'll have to settle for paying attention and getting THIS one detail RIGHT. The FIRST time.

Pull the long white wire through the grommet, to the underside of the chassis. Route it along the inside of the front panel, under the mode switch to the big, empty hole where the "tin can" was installed. Bend the wire to follow along the long side of the big hole, to reach the tie strip at the rear of the chassis, the one next to the metal stud-mount 10-Watt zener diode.

I can't emphasize enough how important it is to get this step RIGHT. The other lugs on this tie strip have high voltages on them. Hook to the wrong one, or create an accidental solder "bridge" across them and POOF! Things will overload and break.

You're nearly finished with the transmitter upgrade, but there's one more axial-lead electrolytic capacitor you haven't used. This one goes in the receiver, below the chassis under the power transformer. The 4700 uf 16Volt axial capacitor will replace a PAIR of 2200 uf capacitors in parallel in the receiver. This ONE part takes the place of the two original capacitors. Because the originals are wired in parallel, the two of them together equaled 4400 uf. The 4700 uf part will be less likely to break down than the old capacitors.



Uh yeah, there are some other things going on in the "After" picture, but you get the idea about C5 and C6, right? In all seriousness, you can't contemplate using this radio in regular service until every, single other electrolytic capacitor has been replaced.

 That's where this picture comes from, a procedure to replace them all. That's why the large yellow cap (C9) disappeared, and the small blue one on the right showed up. But if you think THIS web page is long, the procedure to do a 'scorched earth" replacement of all the electrolytics in both units was TOO long. Too long to get finished yet, anyway. It just makes sense, since the synthesizer runs from the filter caps C5 and C6, to replace them now, rather than worry about whether or not two 30 year-old electrolytic caps will still work well enough to run the synthesizer.

Now that it's all hooked up, you should be good to plug the transmitter back into the receiver, hook up the dummy load and apply power. The digits should flash "88" for about a half second, and then display channel 1.  The brief "88" on power-up is a self-test. If any of the digits has a bad segment that won't light up, you'll see it during the self-test.

The channel frequency depends on both the synthesizer's output frequency, and the one other crystal in the transmitter CR201, 6.545 MHz. If that crystal isn't set right, it will affect the transmitter's channel frequency. Select AM mode and key the mike. An external counter should display the correct frequency for channel 1, 26.965 MHz. If you'd rather not mess with the trimmer cap next to CR201, you can correct the frequency error using the (only) trimmer capacitor on the new PLL.  Unless it's off by more than about 500 Hz, or 5-tenths of a kHz, it probably isn't worth messing with. Unless your frequency counter has been calibrated recently, it may not be any closer than that to start with. You don't have to use an insulated tool for this trimmer cap, but be gentle with it. Takes a pretty tiny blade to fit the slot in this one. 

The reason the slug-tuned coil adjacent to the trimmer cap has a big "X" across it is that you don't need to turn it. Neither of the two slug-tuned coils will have ANY influence on transmitter output. If you try to "peak" either of these while watching the wattmeter, you'll just give the thing (and yourself) a headache. So far, both those slug-tuned coils have proven to be VERY stable, and should not need to be touched for many years. Maybe by then I'll have the instructions written to set them properly. Besides, you need a 'scope to do that anyway.

Now all you should need to do is align the rest of the transmitter. Not sure how long it will take to get that written up, if ever. Like I said, this gadget was designed to be installed by a technician already familiar with this radio.

Last revision Thursday November 3, 2005