[Patrick]

Just got through re-capping and re-wiring. Aligned the IF, couldn't align the RF. The pushbuttons work. But the tuning condenser is wierd. 19, 19A, and 21B are involved. I get only one station when manual tuning, from a fully un-meshed condenser, continuing for about 30 degrees,  then nothing. 21B has very liitle effect, if any.

I know it's probably something really simple, and probably as something to do with 21B, but it is eluding me. And alcohol is NOT involved.  
[Image: http://i1367.photobucket.com/albums/r796...do8rxk.gif]  

[radiohenry]

I have to ask. Does one button switch from automatic to manual tuning? Did you actuate it?
                                                 Henry

[Patrick]

I have to ask. Does one button switch from automatic to manual tuning? Did you actuate it?
                                                 Henry

Yes. The button on the farthest right (in the schematic, too) is for dial tuning. I went over the schematic and the wiring several times to verify that everything was hooked up correctly, and ran continuity on all switch positions to make sure there was good and correct contact. And the band switch is in broadcast. I was able to tune all 7 tuning pushbuttons to stations all across the frequency range. 

[klondike98]

Each pushbutton has its own tuned circuit that is indepdent from the variable tuning cap.

[codefox1]

Yes, but when manual tuning is selected, the whole variable capacitor and associated coils and contact to them are suspect. If there is a short or open in the associated variable capacitor or coils, or fault in the switch, it will not work. Of course, it's usually the other way around, push buttons not working, variable OK, but this is what you appear to have.

[Patrick]

Yes, but when manual tuning is selected, the whole variable capacitor and associated coils and contact to them are suspect. If there is a short or open in the associated variable capacitor or coils, or fault in the switch, it will not work.  Of course, it's usually the other way around, push buttons not working, variable OK, but this is what you appear to have.

That was my first thought. However, all 4 windings of the oscillator coil are fine. I removed it from the circuit before checking since the resistance of each winding is so small. Did the same thing to the switch. All 12 postions are making contact at the proper time. The insulator on the trimmer for 20B is intact. But since the variable cap consists only of metal plates, and I can get one station which I lose when I move the cap, how could it be suspect? What's left in the circuit?  

[Patrick]

What do you think if I run a jumper directly from the variable cap to the #6 (250pfd) on the RF tube. Then run another jumper from terminal 1 of the osc. coil to the det-osc tube. This would bypass all related switches and wiring, just in case there is an intermittant short/open, or in case I missed something?

[Raleigh]

Before you put the oscillator coil back in the radio, you might do two things:

1) Bake the coil in the oven at about 200 degrees F. for an hour or so. (No higher temp, a little lower will be fine.) This will melt off the wax that could be trapping moisture and drive off any moisture that could have been absorbed by the coil form.

I got this advice from Ron Ramirez, who said the wax that was added as a moisture barrier actually traps moisture, so it is just as well to melt it off.

2) Measure the resistance at each terminal, and if any is high, reflow the solder at each connection. You can inspect the connection to make sure the tiny wires are actually being wetted by the solder.

I had a 40-150 (probably with the same coil you have) that would not receive short wave at all. Several of the terminals read around 50 to 60 ohms when they should have read less than 5 ohms (if I remember right.) You might need to use some fresh rosin-core solder rather than just reflowing the existing solder. In my case, it took 2 or 3 tries to get the resistance down below 10, but since reflowing made any difference at all, it meant that the solder connection resistance was a problem.

After baking and reflowing the radio picked up SW really well.

Oops, I see you said you'd removed it from the circuit. I thought you meant you'd removed the coil from the radio. It's still worth a try, and it isn't that hard to pull the coil and put it back in. Make careful drawings and notes about which wire goes where!

[Patrick]

Before you put the oscillator coil back in the radio, you might do two things:

1) Bake the coil in the oven at about 200 degrees F. for an hour or so.  (No higher temp, a little lower will be fine.)  This will melt off the wax that could be trapping moisture and drive off any moisture that could have been absorbed by the coil form.  

I got this advice from Ron Ramirez, who said the wax that was added as a moisture barrier actually traps moisture, so it is just as well to melt it off.

2) Measure the resistance at each terminal, and if any is high, reflow the solder at each connection.  You can inspect the connection to make sure the tiny wires are actually being wetted by the solder.  

I had a 40-150 (probably with the same coil you have) that would not receive short wave at all.  Several of the terminals read around 50 to 60 ohms when they should have read less than 5 ohms (if I remember right.)  You might need to use some fresh rosin-core solder rather than just reflowing the existing solder.  In my case, it took 2 or 3 tries to get the resistance down below 10, but since reflowing made any difference at all, it meant that the solder connection resistance was a problem.

After baking and reflowing the radio picked up SW really well.

Oops, I see you said you'd removed it from the circuit.  I thought you meant you'd removed the coil from the radio.  It's still worth a try, and it isn't that hard to pull the coil and put it back in.  Make careful drawings and notes about which wire goes where!

I actually did remove from the radio. And each coil measured between 2 and 5 ohms. They are supposed to be less than .1 to 2 ohms. Would that increse make a difference? By the way, I already re-installed it. 

[Raleigh]

After I reflowed my coil terminals, some never did get as low as the schematic said, but all were under 6 or 7 ohms, whereas they were tens of ohms before. Based on my experience I'd make a wild guess and say that if yours are all under 5 ohms it ought to be OK without reflowing.

No guarantees, but baking could still help. I was skeptical when Ron suggested baking mine, but I had verified just about everything else--components, tuning condenser, wiring, switch, etc, just as you have, so I didn't have anything else to try. I don't know whether baking or reflowing solder joints fixed mine, because I didn't test it after baking and before reflowing, but the combination of the two worked like a charm.

If you're confident that the tuning condenser has no shorts between plates, and the switch, wiring, and components (including mica caps) are good, baking might be the next thing to try. I pulled a 100 uuf mica the other day that measured over 250 uuf. Conventional wisdom says don't replace micas, but I've had enough bad ones that I don't trust them any more. I test most of them, and replace quite a few.

I haven't looked at the schematic to see where you're planning to put jumpers, and don't have time tonight, but if the jumpers bypass the band switch and wires, but not the capacitors associated with tuning the oscillator, then you don't have anything to lose, and it might detect some problem. I'll see if I can glance at the schematic tomorrow and see where you plan to jumper, but by then you'll have already done it!

[Patrick]

After I reflowed my coil terminals, some never did get as low as the schematic said, but all were under 6 or 7 ohms, whereas they were tens of ohms before.  Based on my experience I'd make a wild guess and say that if yours are all under 5 ohms it ought to be OK without reflowing.

No guarantees, but baking could still help.  I was skeptical when Ron suggested baking mine, but I had verified just about everything else--components, tuning condenser, wiring, switch, etc, just as you have, so I didn't have anything else to try.  I don't know whether baking or reflowing solder joints fixed mine, because I didn't test it after baking and before reflowing, but the combination of the two worked like a charm.

If you're confident that the tuning condenser has no shorts between plates, and the switch, wiring, and components (including mica caps) are good, baking might be the next thing to try.  I pulled a 100 uuf mica the other day that measured over 250 uuf.  Conventional wisdom says don't replace micas, but I've had enough bad ones that I don't trust them any more.  I test most of them, and replace quite a few.

I haven't looked at the schematic to see where you're planning to put jumpers, and don't have time tonight, but if the jumpers bypass the band switch and wires, but not the capacitors associated with tuning the oscillator, then you don't have anything to lose, and it might detect some problem.  I'll see if I can glance at the schematic tomorrow and see where you plan to jumper, but by then you'll have already done it!

No, I haven't jumpered it yet. I've looked at the schematic so much lately that it's becoming a blur. I'll wait for your input.

Pat

[Patrick]

O.K. Rechecked everything. Removed the variable cap & checked it. Went through the adjustments again. Basically the same thing: pushbuttons work all across the frequency range, AND I can adjust the 19A and 21B compensators to 1400hz. However, I cannot adjust the 19 compensator. This type has a nut on the top with access through the chassis. I even removed the nut, and used Deoxit and contact cleaner. Still no oscillations at 580hz. I moved the variable from fully meshed to unmeshed, while feeding the 580Hz, and tweaking the 19 compensator, but can't pick it up anywhere.

[Raleigh]

After reviewing the schematic, I don't think I would jumper as you suggest. If your objective is to test the band switch, I would instead jumper across the switch itself, at each of the points that are connected for the broadcast band. You've already inspected it thoroughly and measured contacts with your ohm meter, so I doubt if that is your problem. If you suspect an intermittent, jumpers won't hurt.

To test the dial/push button switch, your suggested jumper from the antenna side of the tuning capacitor to the switch side of the 250 uuF mica looks like it would do what you want. But since you are receiving a station on the broadcast dial setting, I doubt that switch is your problem.

You need to be sure that there aren't any shorts in your tuning capacitor. You can do this by connecting your ohm meter across the capacitor to ground, setting the meter to beep, and then very slowly turn the capacitor through its range. You need to do this for both sides of the capacitor. If you get any beeps, then inspect to see where any bent vanes are touching or if you have any solder balls or other crud that might be making contact. Carefully bend the vanes so they don't touch or clean away the crud. Blow everything out with canned air if you have it. For a while it seemed like every radio I touched had bent vanes in the tuning cap. It is painstaking and a little frustrating to fix them reliably.

I don't know what you are using for a test antenna. If you are using a random wire for test purposes, I think I'd try to connect the original loop antenna in your cabinet to your chassis to see if that makes a difference. Jumper wires should be fine, or you could take the antenna out of the cabinet. My experience is that you get weird results if you use a random wire with the series 40-1xx radios, but I never had any symptoms quite like yours. The loop antenna (as I understand it) is not just a folded up wire antenna, but its inductance is an integral part of the tuned circuits, and it needs to be there for the thing to work right.

If there are resistors that are suspect, you can measure them in-circuit and be close enough. Most should measure correctly or a little low. If your reading is way off, especially way high, consider changing the resistor. You can check for open capacitors by bridging it with a cap of similar value. There aren't many that would cause this problem, as long as the push-buttons are working.

Always check to see that components are wired properly by tracing the connections through all the terminal strips until you find a connection that you recognize for sure and can't be anything else.

I'm not sure how to test your compensator caps, but you can at least test for leakage with your ohm meter. Each cap should read a complete open, unless possibly there are components that by-pass the cap on both sides. Then you'd probably need to disconnect one side of the cap.

I think I'd try the antenna first, look for tuning cap shorts second (both sides), components third, and only then re-test the switches. It seems like you've done that already, so best move on to something new before re-doing that work.

Keep baking the coil in the back of your mind if you don't get an answer doing these tests, or if one of the experts hanging around here don't suggest anything smarter than I can.

[Raleigh]

One more thing. On a 40-150 I had tuning problems due to worn and decayed rubber grommets holding the tuning capacitor to its bracket. I don't know of a source for repro grommets of this type. Since the cut around the grommet is not in the center, I used a standard grommet from Ace Hardware with a small "O" ring on one side to match very closely the same dimensions as the original grommet. Made a huge difference.

[Patrick]

One more thing.  On a 40-150 I had tuning problems due to worn and decayed rubber grommets holding the tuning capacitor to its bracket.  I don't know of a source for repro grommets of this type.  Since the cut around the grommet is not in the center, I used a standard grommet from Ace Hardware with a small "O" ring on one side to match very closely the same dimensions as the original grommet.  Made a huge difference.

More and different info. Repro grommets are available, and I already replaced them. I'm using the original antenna.

I removed the oscillator coil again, and verified each coil connector. I tested the comp caps. I found one problem that I didn't see the first few times around: either the comp caps were mis-labled on the schematic, or they were wired wrong to the switch. So I re-aligned it using the correct caps. Now I do get 2 weak stations, one at each end of the dial. I still get 7 strong stations with the pushbuttons. 

Now it appears we have solved one problem. 

The same switch position and wiring to the antenna are used whether you use the pushbuttons or the manual dial. So is there anything else that may prevent a strong signal on manual tuning, when pushbutton works fine?  I see nothing.

Oh. When I remeasured the resistance across the osc coil, I got very close readings to what the schematic said.

At least progress has been made!

Pat