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Unique CB needs repair, need help troubleshooting

D

DaveC

Member
Mar 13, 2021
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I have an old Midland midland 77-861 porta-pack 40 chan CB I would like to restore. This one is kind of unique so I would like to get it working even though CBs are a dime a dozen these days.

The issue: It powers on and I hear the typical AM static, seems fine. But when I test it by talking/tapping mic to it with a working walkie talkie the static stops and I get full quieting but no voice is heard. When I TX from that radio the receiving WT just gets a static scratchy noise but no voice.

I also can't seem to find a schematic for this radio anywhere.

Does anyone know what the issue could be?
Thanks.
 
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If you don't mind, I need to get some clarifications on your tests above..... one at a time.

1) "The issue: It powers on and I hear the typical AM static, seems fine."

Does this mean that you turn the Midland on and you hear static/hiss?
------------
2) "But when I test it by talking/tapping mic to it with a working walkie talkie the static stops and I get full quieting but no voice is heard."

Does this mean that you have the Midland on and you key up the Midland microphone and talk into and tap on it.... and THEN the working walkie talkie gets "full quiet but no audio"?

Or.......

Does this mean that when you have the MIdland on and you key it up.... the Midland itself goes quiet?
------------
3) "When I TX from that radio the receiving WT just gets a static scratchy noise but no voice."

Is "that radio" ... the Midland? IN other words is this saying when you key the Midland and talk... the WT only gets scratchy noise but no audio?
----------

In any of this... did you key the walkie talkie on the same channel as the Midland and, if so, did that work at all?

The sense that I am getting from all of the descriptions that you sent is that .... all of those tests were about "keying the microphone on the Midland and describing that you get on the walkie talkie. I am just wondering if the Midland is able to receive from the WT?

I have some information on this one. The 77-861 not the 77-861B.

Just some basic questions......
 
Well since these old radios used the same audio amp for modulation and for transmitting audio I would check to microphone first it may be a cord or connector or cable issue with the microphone. Full quitting you sound like a ham talking about FM coms.
 
The likely cause is the mic. To save space these Midland portables don’t have an internal speaker. The speaker is inside the mic. Unfortunately the speaker also serves as the mic cartridge. This was a common theme used in early walkie talkies. Moisture over time will greatly affect or destroy those cheap paper speakers. Besides the cord, the mic switch could also need cleaning. The 23 channel version I have used the same mic, but I modified mine. By adding an external speaker jack and and replacing the mic jack with a 4 pin connector, I can now use any variety of Cobra mics. A better quality small external speaker can be attached to the bottom with Velcro, but I use mine occasionally in the mobile with a full sized speaker. BTW the 1 watt low power position is great for running an amp.
 
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guitar_199 said:
If you don't mind, I need to get some clarifications on your tests above..... one at a time.

1) "The issue: It powers on and I hear the typical AM static, seems fine."

Does this mean that you turn the Midland on and you hear static/hiss?
------------
2) "But when I test it by talking/tapping mic to it with a working walkie talkie the static stops and I get full quieting but no voice is heard."

Does this mean that you have the Midland on and you key up the Midland microphone and talk into and tap on it.... and THEN the working walkie talkie gets "full quiet but no audio"?

Or.......

Does this mean that when you have the MIdland on and you key it up.... the Midland itself goes quiet?
------------
3) "When I TX from that radio the receiving WT just gets a static scratchy noise but no voice."

Is "that radio" ... the Midland? IN other words is this saying when you key the Midland and talk... the WT only gets scratchy noise but no audio?
----------

In any of this... did you key the walkie talkie on the same channel as the Midland and, if so, did that work at all?

The sense that I am getting from all of the descriptions that you sent is that .... all of those tests were about "keying the microphone on the Midland and describing that you get on the walkie talkie. I am just wondering if the Midland is able to receive from the WT?

I have some information on this one. The 77-861 not the 77-861B.

Just some basic questions......
Click to expand...
1, Yes I turn on the Midland and hear static. It sounds the same as the typical static on working units.
2 It means I have the Midland on and I key up the WT. Just as if I am communicating to the midland with a WT. I get full quieting on the Midland but no audio.
Yes both were on the same channel.

Then I did the opposite test, tried to TX with the Midland and listened to the WT. The WT received static popping noises but no audio from the Midland.

It is like Midland is RX/TX the carrier but no audio.

Also of note I have two of these same radios, one works one doesn't (as described). I performed these same tests with the working radio and everything worked as it should. I even tried the mic from the working radio to rule out a bad mic.
 
There’s the same 861 schematic that's been floating around on different sights, but a low resolution one that’s barely readable at best. Zooming in on it will reveal no further details. I have several thoughts that it could be the PLL crystal or a bad cap, but you really need the SAM’S to help trouble shoot that baby. Most of the SAM’S books sell used under $10 with shipping on Ebay. TIP: Get the book, not a copy of the radio ripped from the SAM'S selling for more than twice the price.
 
sunbulls said:
There’s the same 861 schematic that's been floating around on different sights, but a low resolution one that’s barely readable at best. Zooming in on it will reveal no further details. I have several thoughts that it could be the PLL crystal or a bad cap, but you really need the SAM’S to help trouble shoot that baby. Most of the SAM’S books sell used under $10 with shipping on Ebay. TIP: Get the book, not a copy of the radio ripped from the SAM'S selling for more than twice the price.
Click to expand...
It sounds like it will be quite difficult to repair for a novice like me. I don't have a room full of test equipment or an EE degree. I can solder out/in parts but that is about it. I was hoping maybe it was a common issue that someone would say "it sounds like the XXX transistor is bad as I have had that happen before" or something to that effect. It was worth a shot. I suppose it can go on ebay as "for parts not working".
 
DaveC said:
It sounds like it will be quite difficult to repair for a novice like me. I don't have a room full of test equipment or an EE degree. I can solder out/in parts but that is about it. I was hoping maybe it was a common issue that someone would say "it sounds like the XXX transistor is bad as I have had that happen before" or something to that effect. It was worth a shot. I suppose it can go on ebay as "for parts not working".
Click to expand...
If and when you decide to sell it, be sure to include a good photo of the leather case, opened battery compartment, plus antenna. It should fetch a fair price if those items are in good shape. Either the leather case is shot, missing, or the battery terminals are corroded with many of those portables. Owners or collectors are looking for those particular replacements above all else.
 

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