Broken radio repair: tech advice?

[DaveC1964]

I have an old Midland midland 77-861 porta-pack 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 static, seems fine. But when I test it by talking to it with a working WT 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 sound 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.

 

[hypersight]

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/%23KF/Midland/MIDLAND%2077-861.jpg

Not sure if you are able to read all of it.

 

[FPR1981]

I have an old Midland midland 77-861 porta-pack 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 static, seems fine. But when I test it by talking to it with a working WT 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 sound 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.

These radios are cool. I have both versions, the 40 channel and the 23 channel. I have the leather case, fully intact, with the portable antenna too.

It sounds like it's off frequency, BUT, I have encountered at least three old CB's very recently that I thought were off frequency, and it was nothing more than dirty contact points. Midlands were notorious for the tuners being dirty and making intermittent contact. I have had two do that, I had a President Teddy R with dirty contacts that wasn't TXing or RXing properly and I had a Cobra 142 GTL that the band selector switch was so dirty it would not make proper contact.

All were fixed with air duster spray and contact cleaner. Give that a try first.

 

[DaveC1964]

These radios are cool. I have both versions, the 40 channel and the 23 channel. I have the leather case, fully intact, with the portable antenna too.

It sounds like it's off frequency, BUT, I have encountered at least three old CB's very recently that I thought were off frequency, and it was nothing more than dirty contact points. Midlands were notorious for the tuners being dirty and making intermittent contact. I have had two do that, I had a President Teddy R with dirty contacts that wasn't TXing or RXing properly and I had a Cobra 142 GTL that the band selector switch was so dirty it would not make proper contact.

All were fixed with air duster spray and contact cleaner. Give that a try first.

Thanks. If it is off frequency how is that repaired? Is there a way to test it to see if that is the issue?
If it was off frequency would I get quieting when keying up the other radio?

 

[FPR1981]

Thanks. If it is off frequency how is that repaired? Is there a way to test it to see if that is the issue?
If it was off frequency would I get quieting when keying up the other radio?

Possibly, because they typically drift to the point you get a little bit of TX and RX interacting with a close by unit.

You need to thoroughly clean everything inside it with contact cleaner first and then branch out from there. These suck to work on because everything is crammed tight

 

[FPR1981]

The 23 channel version I own was inside the leather case and the inside was beyond disgusting. It had more dust and dirt than I've ever seen inside a radio.

If cleaning does not remedy the issue, you need to put it on a set of meters to check output power and modulation. Then check it on a frequency counter.

If it's off, you need to look at a service manual to see if and how it can be tuned.

 

[wtp]

if you transmit too close the AGC might totally silence the radio.

 

[DaveC1964]

if you transmit too close the AGC might totally silence the radio.

I put the transmitting WT on low power. Also I have a working unit like the broken one and that one TX/RX fine doing this. Something is definitely off on this one.

 

[DaveC1964]

The 23 channel version I own was inside the leather case and the inside was beyond disgusting. It had more dust and dirt than I've ever seen inside a radio.

If cleaning does not remedy the issue, you need to put it on a set of meters to check output power and modulation. Then check it on a frequency counter.

If it's off, you need to look at a service manual to see if and how it can be tuned.

Yeah I don't have all of that equipment except for a volt meter. I wouldn't know what should be what though. I am no tech, I have a little knowledge but not much. I can solder in new parts and do basic testing. That is why I asked here, I was hoping someone would know the problem and say "it sounds like the xyz transistor is blown". Then I could go from there.

 

[FPR1981]

Yeah I don't have all of that equipment except for a volt meter. I wouldn't know what should be what though. I am no tech, I have a little knowledge but not much. I can solder in new parts and do basic testing. That is why I asked here, I was hoping someone would know the problem and say "it sounds like the xyz transistor is blown". Then I could go from there.

Is this the 23 or 40 channel version? If you want an assessment and at least the basics of what I described, if you felt comfortable shipping it to me, I can hook it up to my equipment and see what we're getting.

Do you by chance have the 5 pin DIN power plug? I don't, but would love to see exactly how it is wired.

The 40 channel version I have was property of the Pennsylvania DOT and was very well cared for. These are cool radios.

 

[press1280]

I have a Navajo base station that was sort of doing what yours is doing. The question I'd have for you is when the WT transmits, are you getting the Midland's signal meter going all the way up, or does it actually go down?
An SDR dongle would help "find" where you're actually transmitting.

 

[DaveC1964]

Is this the 23 or 40 channel version? If you want an assessment and at least the basics of what I described, if you felt comfortable shipping it to me, I can hook it up to my equipment and see what we're getting.

Do you by chance have the 5 pin DIN power plug? I don't, but would love to see exactly how it is wired.

The 40 channel version I have was property of the Pennsylvania DOT and was very well cared for. These are cool radios.

It is the 40 channel version. I don't have the power plug. A post above linked to a schematic but it is a bit low res. You should be able to see the power socket pinout from that though.

 

[DaveC1964]

I have a Navajo base station that was sort of doing what yours is doing. The question I'd have for you is when the WT transmits, are you getting the Midland's signal meter going all the way up, or does it actually go down?
An SDR dongle would help "find" where you're actually transmitting.

Ok I can test that, I didn't look when I was playing with it. It is not set up at the moment.