MR8100: MR8100 Quiet Audio

[cpg178]

Just got my hands on a near mint condition MR8100, an awesome device so far that's picking up signals with no antenna connected that my BCT15x pulls in with a lot of distortion. The only issue is that the audio is very quiet on the original Uniden SP1. Is this normal, and if not is there a known fix?

 

[trentbob]

It's been so long since I had one of those, no external speaker of course but the volume was not an issue for me.

Some interesting things I do remember was you could program it by computer but I think you would need some kind of software now on today's computers to program it through the latest windows. Pretty sure it was a floppy disk.

If you search hard enough you can probably find the codes that you could enter to make modifications on this radio and expand its frequency coverage, it was made for public service, Common Sense things like big knobs and display LOL.

Only dual conversion and was subject to a lot of intermod, good luck with your new radio and I hope you find an answer to the low audio.

 

[cpg178]

It's been so long since I had one of those, no external speaker of course but the volume was not an issue for me.

Some interesting things I do remember was you could program it by computer but I think you would need some kind of software now on today's computers to program it through the latest windows. Pretty sure it was a floppy disk.

If you search hard enough you can probably find the codes that you could enter to make modifications on this radio and expand its frequency coverage, it was made for public service, Common Sense things like big knobs and display LOL.

Only dual conversion and was subject to a lot of intermod, good luck with your new radio and I hope you find an answer to the low audio.

Thank you, got a hold of some software that needs DOS to program it which I can run a DOS emulator on my win10, just waiting on the proper cable to come in. All connections seem to be good and scanner works great aside from this quiet audio

 

[kevino]

FWIW, the code to restore "full 800 MHz coverage" was "ECPA1986" (nobody would EVER guess that one ). Useless since cellular signals are now digital. An old note I found said that it would only do 12.5 kHz steps in the 800 cellular band but those channels were spaced 30 kHz apart.

 

[kevino]

Just got my hands on a near mint condition MR8100, an awesome device so far that's picking up signals with no antenna connected that my BCT15x pulls in with a lot of distortion. The only issue is that the audio is very quiet on the original Uniden SP1. Is this normal, and if not is there a known fix?

Possible that there is a problem with the speaker itself? Have you tried another speaker or a set of headphones?

 

[cpg178]

Possible that there is a problem with the speaker itself? Have you tried another speaker or a set of headphones?

I did add 2 quick connects on the speaker feeds due to a frayed cable which was my initial thought of the low audio cause. But I will hook it up to a Motorola speaker and try that out

 

[tvengr]

It has been my experience that low audio with old scanners is usually due to bad electrolytic capacitors in the audio amps which have lost most of their value. Also check for bad solder connections. Bad solder connections on circuit boards tend to fail after about 10 or 15 years.

 

[trentbob]

I did add 2 quick connects on the speaker feeds due to a frayed cable which was my initial thought of the low audio cause. But I will hook it up to a Motorola speaker and try that out

If you are comfortable taking the radio apart, look for a short maybe caused by metal pieces used to hold the Jack securely, they could be shorting out your connection and it would just be a matter of moving them out of the way?

 

[RFI-EMI-GUY]

You might want to verify that the receiver is on frequency. If the TCXO has drifted , the discriminator will be off center and coupled with the narrowbanded channels, the audio may sound weak. Try tuning a strong weather channel and tune off channel +/- 5 KHz. It should sound about same off channel either way. By the way I acquired an SP-1 speaker recently for my MR8100 and found the wires had never been soldered to the speaker lugs.

 

[cpg178]

Thanks everyone for the input, will try some of these things out to see if it helps.

 

[RFI-EMI-GUY]

Thanks everyone for the input, will try some of these things out to see if it helps.

Please keep us posted as to your findings. There is a block diagram available, but no detailed schematic to my knowledge.

Did you get an original bracket with yours radio? If so, I would be interested in a picture and measurements. Part number if any stamped on it would be most helpful.

 

[cpg178]

No part number on it

 

[cpg178]

So i cracked it open, everything looks alright except this small capacitor that is only connected on 1 leg to the antenna connector

 

[donc13]

Visually, that capacitator has never been connected as the free end looks to be totally free of solder.

If that's not true, if there is solder on it, my GUESS is that it goes to that pad on the circuit board at then end of the L622 label. Pure guess. A schematic would help. Obviously.

 

[RFI-EMI-GUY]

So i cracked it open, everything looks alright except this small capacitor that is only connected on 1 leg to the antenna connector View attachment 128346

Same in mine and reportedly in others. One rumor is that grounding the loose end lowers the 800 MHz cellular signal received and improves receiver IMD. I left mine flying in the air as found.

 

[mc48]

Did you connect the green wire to anything? The green wire mutes the audio if you connect it to ground, normally it was connected to a mic hang-up box. There is also a diode that if the green is connected to power will burn out and drop out the audio.

 

[cpg178]

Did you connect the green wire to anything? The green wire mutes the audio if you connect it to ground, normally it was connected to a mic hang-up box. There is also a diode that if the green is connected to power will burn out and drop out the audio.

Are you referencing the green wire that is part of the power harness?

 

[mc48]

Yes, one of the three.

 

[cpg178]

Yes, one of the three.

That wire is not connected to anything

 

[RFI-EMI-GUY]

That wire is not connected to anything

That is the normal condition for the green /mute wire. Did you look inside the SP1 speaker? Mine had the wires wrapped, never soldered onto the speaker tabs.