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Post by Deleted on Feb 17, 2009 11:17:12 GMT -5
As I posted in another post, I received an Eico 635 tube tester (OK, not the best tester) from a local ham. He is actually the president of the local radio club I joined. I donated a scope to the club, and he gave me the tube tester and 2 boxes of tubes.
Upon using the tester, I noticed some of the tube had about a 30 second response time, and that new tubes are measuring 75%. I am assuming it is the tube tester. Anyway, after measuring each tube, I found a bad final 6BQ5. It measured around 40%. Upon replacing this, the receive has at least partially come back. I hear closer radios now, where before I could not hear anything. The DK is still coming and going. and the meter will not work on receive, even if one of the real close radios is busting thru.
But I at least have a starting point.
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Post by Deleted on Feb 17, 2009 21:59:05 GMT -5
More progress! I got receive back. I found an open resistor (100K feeding pin 6 of V3). That was open and replacing it brought back the receive. Thanks to Nomad as a Google found a note from him on those resistors. I still have 2 problems.
1. Transmit is intermittent. More off than on. The DK goes down to 0 when I key up, but does swing to 1 when I whistle, and the mod lights works.
2. White noise. This radio seems to have alot of it. Any way to reduce it?
I want to align this radio, but how the hell do you loosen those slugs inside those cans?
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Post by Tombstone (R.I.P.) on Feb 18, 2009 9:04:46 GMT -5
Glad that you got the recieve back. The resistor that you found open is probably the one I was talking about that will shut off receive and couldn't remember which one it is. To get those slugs to turn, heat them a bit with your soldering iron and gently try and turn them back and forth until they will turn enough to get an adjustment. Their fragile so you sure don't want to crack one. I don't think that I need to tell you this but don't use a screwdriver, use the correct shaped non conductive alignment tool. Speaking of alignment, yesterday I aligned the receive on my Dynascan Cobra 2000 an got about two more S units showing on the meter when I used my B&K signal generator. Trouble is now that I have intermittent noise that sounds like an electric motor sarting and stopping and my peak job brought that up too.
Tombstone
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Sandbagger
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Post by Sandbagger on Feb 18, 2009 9:13:54 GMT -5
More progress! I got receive back. I found an open resistor (100K feeding pin 6 of V3). That was open and replacing it brought back the receive. Thanks to Nomad as a Google found a note from him on those resistors. I still have 2 problems. 1. Transmit is intermittent. More off than on. The DK goes down to 0 when I key up, but does swing to 1 when I whistle, and the mod lights works. 2. White noise. This radio seems to have alot of it. Any way to reduce it? I want to align this radio, but how the hell do you loosen those slugs inside those cans? Two things to check real quich for that intermittent TX: Check for dirty tube sockets and make sure the pins all make good contact. Clean the relay contacts. I had a similar problem with my Hy-Gain 623, and cleaning the relay (and actually bending contacts a bit) solved it.
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Post by Deleted on Feb 18, 2009 9:46:21 GMT -5
I engage the relay manually with a plastic tool, and shows about 4 watts. While I am holding onto the relay, I key the mic and the DK just drops out. I tried different mic. Almost like the mic is loading it down.
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Post by Sandbagger on Feb 18, 2009 11:52:21 GMT -5
I engage the relay manually with a plastic tool, and shows about 4 watts. While I am holding onto the relay, I key the mic and the DK just drops out. I tried different mic. Almost like the mic is loading it down. There is nothing in the relay keying circuit that could be "loaded down". All the mic does is provide a path to ground through its PTT switch to energize the relay. I would have to say that, based on what you've said, the problem is in the relay. Give those contacts a good cleaning and maybe a little realigning.....
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Post by Deleted on Feb 19, 2009 10:07:52 GMT -5
No dice. I completely tore apart the relay, and burnished every contact to a polished gold. The transmit does occasionally show 4W, especially when I engage it manually, and while I am holding the relay down, and then key the mic, the DK drops out. I figure I can get a DK my manually engaging the relay about 50% of the time.
I looked at the schematic and you are right as nothing in the mic is loading it down. But keying the mic kills the DK. I have a faulty component that is weak and teeters on failing when the mic is keyed. I wish I could locate it as that is the past problem with this radio.
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Post by Sandbagger on Feb 19, 2009 17:41:21 GMT -5
No dice. I completely tore apart the relay, and burnished every contact to a polished gold. The transmit does occasionally show 4W, especially when I engage it manually, and while I am holding the relay down, and then key the mic, the DK drops out. I figure I can get a DK my manually engaging the relay about 50% of the time. I looked at the schematic and you are right as nothing in the mic is loading it down. But keying the mic kills the DK. I have a faulty component that is weak and teeters on failing when the mic is keyed. I wish I could locate it as that is the past problem with this radio. Then the only thing I can think of, is that the voltage which feeds the relay is being pulled down because there is a resistor that has increased value thereby limiting the available current. I would check to see what the voltage drops to when the mic is keyed, and if it drops appreciably, check R27 and R28.
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Post by BionicChicken on Feb 19, 2009 18:41:52 GMT -5
Are you getting keying voltage to the relay coil? Is the relay even trying to key with the mike? Maybe something in the keying circuit is what is wrong
BC
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Post by Deleted on Feb 19, 2009 22:54:29 GMT -5
The relay keys solidly. I did replace both the R27 and R28 with equiv metal oxide resistors. It is the weirdest thing.
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Post by BionicChicken on Feb 20, 2009 7:24:00 GMT -5
Apply an external voltage to the coil. Either 12vdc or 110vac with the radio unplugged and off to key the relay then take an ohm meter and see which contact is not making. Can you key it with the mike and then just touch one contact and make the wattage come up? Just stinking....I mean thinking out loud.
BC
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Sandbagger
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Post by Sandbagger on Feb 20, 2009 7:52:14 GMT -5
The relay keys solidly. I did replace both the R27 and R28 with equiv metal oxide resistors. It is the weirdest thing. If the voltage feeding the relay isn't sagging, then there is no difference between the relay being keyed electrically, and manually, except for the level of force used. So we're back to contact alignment. You might try bending the transmit contacts up very slightly to see if they make better contact when keyed.
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Post by Tombstone (R.I.P.) on Feb 20, 2009 7:57:39 GMT -5
I'm thinking along the lines of low voltage somewhere too. Do the front panel lights dim when you dead key with the mic? It could be that the radio's power supply is failing under load. If you have the 12 volt power cord for the radio you can try using an external supply. I think that there were problems with the power transformer in that style chassis radio but it seems like your problem shows up when you key the mic and engage the modulation section. There might be something shorted that's putting an excess load on the power supply and dragging everything down. All just guesses and places to look.
Tombstone
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Post by Tombstone (R.I.P.) on Feb 20, 2009 8:05:35 GMT -5
Another thought.......voltage regulator?
Tombstone
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Post by Deleted on Feb 20, 2009 9:12:56 GMT -5
If the regulators are those 2 transistors on the back panel, I checked them and they held voltage while keyed. I will focus on the relay again. This is so weird.
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Post by Sandbagger on Feb 20, 2009 11:19:19 GMT -5
If the regulators are those 2 transistors on the back panel, I checked them and they held voltage while keyed. I will focus on the relay again. This is so weird. Those two big transistors on the back are not regulators, they're multivibrators that are used when you run the radio off of 12V DC, and they turn the DC into AC so that it can be stepped up by the transformer. The only regulated voltage in that rig is what is feeding the solid state PLL board. Most tube rigs do not use voltage regulators and there usually will be some voltage change when going from receive to transmit. I'm still thinking there is some issue with that relay. If you can put the relay down and it transmits fine, and there is no voltage sag when you key the mic, then the only difference is in how much force is applied to the relay.
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Post by Deleted on Feb 20, 2009 22:46:21 GMT -5
Multivibrators? I guess that is where my tube theory limitations come in. Weren't they big cans? Almost capacitor-like looking?
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Post by Sandbagger on Feb 20, 2009 22:50:35 GMT -5
Multivibrators? I guess that is where my tube theory limitations come in. Weren't they big cans? Almost capacitor-like looking? That's a vibrator. A mechanical device that makes AC out of DC. A Multivibrator is a solid state replacement.
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Post by BionicChicken on Feb 20, 2009 22:55:44 GMT -5
Try taking an insulated tool and while keying the mike touch the individual contacts one at a time to see if you can make the wattage come up to normal. This has worked for me in the past especially on amplifiers.
BC
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Post by Deleted on Feb 22, 2009 19:31:25 GMT -5
OK. I found a couple things. I measures the voltage R501 (5K 10W), on the L402 side of the resistor, and it measures about 215V. I then manually key the relay with a plastic tool, and the voltage only drop a couple volts. However, and I key the relay with the mic, the voltage drops to 96V.
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Post by Tombstone (R.I.P.) on Feb 23, 2009 5:27:05 GMT -5
Voltage drop problem, now all you have to find is where and why. I still think that it's worth looking at the internal power supply.
Tombstone
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Post by Sandbagger on Feb 23, 2009 8:02:56 GMT -5
OK. I found a couple things. I measures the voltage R501 (5K 10W), on the L402 side of the resistor, and it measures about 215V. I then manually key the relay with a plastic tool, and the voltage only drop a couple volts. However, and I key the relay with the mic, the voltage drops to 96V. Something's not right. On my schematic, L402 is the last receive IF transformer before the detector stage, and there is no connection to R501. Now R501 is the current limiter(voltage dropper) for the relay. On the relay side of the resistor, it's perfectly normal for the voltage to drop, since the relay coil is probably a 110 V. If you don't key the mic (and provide the circuit to ground through the relay), there won't be much voltage drop. Now it is possible that the 96V that you're seeing is a tad low to fully pull the relay in, so the value of R501 might have drifted a little high. Or if the voltage on the other side of R501 is dropping more than it should, then you have to trace back through R27 and R28 and check the filter caps C27, C28, C29, and C30.
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Post by Deleted on Feb 23, 2009 8:57:14 GMT -5
I replaced all those caps. I was confused by the schematic. That makes sense on the voltage drop across the relay, as I didn't know it was that high. I think it is soldered at L402 on an unused terminal, as there are 6 terminals there. Only 5 are listed on the schematic. I checked a Robyn 123B, and it is the same way. Also, when I replaced those resistors, I typically cut the leads, and resolder to the leads, as it was easier to do that than to unsoldered all the way at the terminal.
The relay measures fine, and is strong. While everything points to the relay, it is not it.
The other thing I noticed it that when I finally do get a DK with the mic keying, as soon as I speak into it, it drops out again.
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Post by Sandbagger on Feb 23, 2009 14:32:17 GMT -5
I replaced all those caps. I was confused by the schematic. That makes sense on the voltage drop across the relay, as I didn't know it was that high. I think it is soldered at L402 on an unused terminal, as there are 6 terminals there. Only 5 are listed on the schematic. I checked a Robyn 123B, and it is the same way. Also, when I replaced those resistors, I typically cut the leads, and resolder to the leads, as it was easier to do that than to unsoldered all the way at the terminal. The relay measures fine, and is strong. While everything points to the relay, it is not it. The other thing I noticed it that when I finally do get a DK with the mic keying, as soon as I speak into it, it drops out again. What are the voltages off of that supply? The voltage heading to the relay should be about 220V on receive and it'll drop down to around 195V on transmit. It the voltage sag is much more than that, there's a supply problem.
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Post by Deleted on Feb 23, 2009 23:58:33 GMT -5
OK. All supply voltages check out, even during transmit, except:
the 197V during transmit at the brown wire on the CB-PA switch is not there during transmit.
Also, the -85V that is supposed to turn into -3.25V during transmit, is not there. It is more like - 0.4V
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Post by Sandbagger on Feb 24, 2009 7:47:01 GMT -5
OK. All supply voltages check out, even during transmit, except: the 197V during transmit at the brown wire on the CB-PA switch is not there during transmit. Also, the -85V that is supposed to turn into -3.25V during transmit, is not there. It is more like - 0.4V I can't tell from the schematic which pin on the PA/CB switch is the brown wire. But that switch is fed by the relay and one part of it will have voltage only on transmit, while the other will have voltage on it only on receive, so what you're seeing may be perfectly normal. The -82V supply serves 2 purposes. First off, it provides the proper bias for the squelch control to function properly. That voltage is also applied to the control grid of the transmit final tube on receive to drive it into hard cutoff to prevent self-oscillation. On transmit, the relay shorts the output of R26 to ground, so the voltage will drop in TX. Be careful of the small .1uF electrolytics in that circuit C23, 24 and .01uF C25. Those are the ones that are notorious for becoming firecrackers when you least expect it. That aside, if the 197V holds on TX, then your power supply is healthy and you should have transmit. The fact that we keep coming back to the relay, makes me want to just tell you to replace it with another one and see what happens.
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Post by Deleted on Feb 24, 2009 14:00:23 GMT -5
I measures the -82V at the point where R25, C25, and C901 come together. That this point when I go into transmit, the voltage should be -3.25V. But it is -0.4V. I will double check the -197V
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Post by Deleted on Feb 25, 2009 22:30:51 GMT -5
I have about had it with this thing. I remeasured the relay, and it is good. Supply voltages seem good. The only odd voltage is that -3.25V. I am not getting it. I am getting -0.4V.
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Post by Sandbagger on Feb 26, 2009 8:55:26 GMT -5
I have about had it with this thing. I remeasured the relay, and it is good. Supply voltages seem good. The only odd voltage is that -3.25V. I am not getting it. I am getting -0.4V. That voltage difference would not account for your transmit problem. My Comstat still transmitted even when the -82V was gone (due to an open cap). The only odd thing was the fact that if you pushed on the relay manually, the transmit worked. Based on the fact that the voltages look good and they do what they're supposed to, I just can't get past the likelihood that the relay contacts are just not making a good connection when the relay is keyed, but the extra force that you apply manually, allows it to work.
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Post by Deleted on Feb 26, 2009 19:25:44 GMT -5
I have about had it with this thing. I remeasured the relay, and it is good. Supply voltages seem good. The only odd voltage is that -3.25V. I am not getting it. I am getting -0.4V. The only odd thing was the fact that if you pushed on the relay manually, the transmit worked. Based on the fact that the voltages look good and they do what they're supposed to, I just can't get past the likelihood that the relay contacts are just not making a good connection when the relay is keyed, but the extra force that you apply manually, allows it to work. Well, not always. In fact, if I manually push the contacts in with a plastic tool, the Transmit works about 1 out of 10 times. When I can get it to work manually, I then hold it down and key the mic, and it immediately drops out. It's definitely not the relay. I don't think it's tubes. I changed out all electrolytics. How often do disc caps go bad? How about diodes shorting?
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