Hello All,
I'm working on a GM AM-FM radio from 1976. I cannot find any model number on it anywhere. There is a tiny piece of the label on it. But the model number is gone. This radio was fully operational before it was shipped. It was packed wrong so it had a collision with the inside of the box. The place of impact was near the audio transformer that's attached to the back. The end fin on the heat sink was also bent. Now the amplifier powers up (nice thumps!) but the tuner does not. On the FM band, no matter where I tune, the FM light no longer comes on. I cannot see anything physically wrong. I have straightened out the bends so it no longer looks like anything happened. But something did somewhere. I don't see any broken lands but something happened. Where should I look?
Does anyone have any idea what model this is? It has the dial cord that changes the entire dial scale when AM or FM is selected. It has 5 push buttons. A button at one end says "AM" on it and the other one says "FM" on it. There are connections on the back for the usual Left Right, power, dial Lamp and negative.

Please help if you can.

Thanks,

Dave

I would bet it has a crack in the PC board. Most like where the point of impact. Take all the covers off, look around all the edges where it connects to the metal frame. Tighten up all the ground screws while your at it.

Warren,
I have checked the PC boards with a very bright lamp and can find no such broken lands or cracked boards. I am going to need to find the schematic or at least the model number so I can find the schematic. Then I can do some troubleshooting.

Thanks,

Dave
:I would bet it has a crack in the PC board. Most like where the point of impact. Take all the covers off, look around all the edges where it connects to the metal frame. Tighten up all the ground screws while your at it.
:
:

Hello All,
I do have sound from one channel. I have the thump from both channels but one has no sound. The balance control is good. So what may have broken? Where do I look? With no service data, I am lost.

Thanks,

Dave
:Warren,
: I have checked the PC boards with a very bright lamp and can find no such broken lands or cracked boards. I am going to need to find the schematic or at least the model number so I can find the schematic. Then I can do some troubleshooting.
:
:Thanks,
:
:Dave
::I would bet it has a crack in the PC board. Most like where the point of impact. Take all the covers off, look around all the edges where it connects to the metal frame. Tighten up all the ground screws while your at it.
::
::
:

Hello Again All,
If I am getting sound from one channel it means that the tuner is working and then several things could be going on. One would be that something happened to the other output from the multiplex decoder chip, or there is a problem in the buffer transistor circuit or maybe something happened to one of those white "networks" near the buffer transistor. But the problem is definitely somewhere in between the Multiplex decoder and the output, since the output is working and the tuner is working. The stereo light does come on for a Stereo station. This leads me to believe that the MPX Decoder is working fine.

Thanks,

Dave
:Hello All,
: I do have sound from one channel. I have the thump from both channels but one has no sound. The balance control is good. So what may have broken? Where do I look? With no service data, I am lost.

Thanks,

:Dave
::Warren,
:: I have checked the PC boards with a very bright lamp and can find no such broken lands or cracked boards. I am going to need to find the schematic or at least the model number so I can find the schematic. Then I can do some troubleshooting.
::
::Thanks,
::
::Dave
:::I would bet it has a crack in the PC board. Most like where the point of impact. Take all the covers off, look around all the edges where it connects to the metal frame. Tighten up all the ground screws while your at it.
:::
:::
::
:

Does it have sound on both channels in the AM mode? That should tell you if it's an FM problem, or in the audio path common to both AM an FM. You said it was working before it got bent in shiping. I would still think there is an open other than componet fail. Try and flex and probe the circuit board while it's playing. You could also do some simple testing, as to use the working channels voltage path,compaired to the non working one.

Warren,
The one channel that does not work in FM also does not work in AM. I have flexed boards and it makes absolutely no difference. I do not have any service data or model number so I do not know where the signal path is exactly. I can only guess. I will eventually find the problem though.

Thanks,

Dave
:Does it have sound on both channels in the AM mode? That should tell you if it's an FM problem, or in the audio path common to both AM an FM. You said it was working before it got bent in shiping. I would still think there is an open other than componet fail. Try and flex and probe the circuit board while it's playing. You could also do some simple testing, as to use the working channels voltage path,compaired to the non working one.
:

Is this like your radio ? The model is listed in the ad.

http://cgi.ebay.com/ebaymotors/1975-80-PONTIAC-FIREBIRD-TRANS-AM-AM-FM-RADIO_W0QQitemZ3601785

Google 1976 pontiac trans am radio. Ebey motors did show a listing.

Delco Tag# 52AFM-1,
Results on Google are only for the car but not the radio. I can find zero matches for the radio.

Thanks,

Dave

:Google 1976 pontiac trans am radio. Ebey motors did show a listing.
:

Delco Tag% 52AFM-1,
I searched eBay and found nothing there either.

Thanks anyway,

Dave
:Google 1976 pontiac trans am radio. Ebey motors did show a listing.
:

The radio that " Was " listed on Ebey motors must have sold. But it was exactly the radio you described.
The Delco tag number is the model number 52AFM-1 look that model up in Sams.