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 Post subject: 1966 AM radio repair - mustang
PostPosted: Feb Mon 26, 2018 10:40 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
I've just joined this forum and hope to learn about DIY repair of my radio. I'm not sure if my old '66 AM Ford radio is old enough to be worthy of a post, but thought I'd try and maybe learn something. This seemed the best antique radio forum out there based on some searching, so thanks in advance if anyone can help.

I have two old AM radios from 1966 mustangs, (one being original to my car) and hope to get a working unit in the dash. I've purchased the Sams Photofact manual for my 6TPZ model and fond the parts list and diagrams very helpful. I had read (and hoped) that by replacing the electrolytic capacitors I might restore operation, but no. I carefully replaced all the electrolytics shown (C1 - C4, 6 caps in total) with new and ensured correct polarity. So far, I've managed to get only a "pop" sound as the unit is switched on, but nothing more. Same situation on both units, so I'm missing something. I do have an antenna plugged in and sticking outside of the garage. A new speaker too. Running power from car battery via jumpers. Can anyone offer a clue as to where to look next, which section of the schematic to look for components that are failure-prone that could cause this? I am not schooled in electronics, and have only a DVM, a soldering iron kit and patience! Any input is greatly appreciated.


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Feb Mon 26, 2018 11:39 pm 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 362
Location: Stone Mountain, GA
Does your schematic include voltages?
If so, check the transistor voltages. Those old germanium ones are prone to fail.

_________________
Scott.
Powered by infinite improbability drive.


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Feb Wed 28, 2018 2:08 am 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Thanks for the reply. Yes, the schematic shows voltages, so good idea to check. Now I need to do some research and learn how to do it!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Feb Wed 28, 2018 8:38 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1710
Location: Shelton, WA
The pop indicates the output stage of your radio is working. That's the output transistor. Most likely the detector transistor is bad but could be one of the other ones. You want to take voltage readings at the emitter base and collector of these and if anything is amiss check it out of circuit. This board to service is a real pain in the a-- the way it is mounted and where the components are located.

If you have a signal tracer or generator it will help in locating the defective stage.

LOL

billn


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Feb Wed 28, 2018 9:46 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Thanks for the reply. It's great that the Output transistor seems to be good. There are 6 transistors in total and it's the most expensive one to replace (a new GE-3 equivalent NTE 121 transistor = $28). I've noticed that pictures of reconditioned radios for sale all seem to retain the original AR14 transistor prominently mounted on the front outside surface, so they seem to be very reliable.

The other 5 transistors are labeled in the parts list as:
RF Amp
Conv.
IF Amp
1st AF Amp
2nd AF Amp

Do you know which one would be the detector transistor you mentioned?

And yes, the board removal required some thought and some practice. I have 2 radios to experiment with, so I've mastered it now. I can remove the board by unsoldering only one wire, leave other wires connected and carefully extract it and flip it over for inspection and soldering.

Thanks for your guidance! I'm learning new things and having some fun too.


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Feb Wed 28, 2018 10:59 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1710
Location: Shelton, WA
X2 is the converter xsistor. At the bottom of the board look at it from the top back. To the left of the big filter can

billn


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Feb Wed 28, 2018 11:36 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Okay got it. The X2 is clearly illustrated in the Sams Photofact manual too, so I can't mess-up. I'll buy a new one and replace it to see if it helps. The transistors are only $5, so cheap fun! I'll post results once I've done the deed. Thanks for lending your expertise!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Thu 01, 2018 1:12 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5561
Location: Indianapolis, IN
Hello & welcome to ARF, Dels !

Along with the "pop" when you apply power, can you hear a slight "hiss" in speaker with your ear next to it when turned all the way up ? If so, try carefully touching your meter probe to all the connections around volume control one at a time to see if you get a "click" or noise.

Before you buy or replace anything, worth looking into a bit further...

John


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Thu 01, 2018 1:37 am 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Thanks for the reply. I'll poke around the switch too, as you recommend. I can't hear any hiss, but my hearing is not that great anymore. Maybe good to just carefully re-flow the solder connections to ensure no cold joints. I have plenty of time to try things. Thanks!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Thu 01, 2018 4:24 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5561
Location: Indianapolis, IN
Another thing I thought of---what are you using for antenna and how is it connected ?

If you're using an actual car antenna, make sure that the center pin and outside metal shell of connector plug is not shorted.

If using just a length of wire inserted in center hole of receptacle on radio, make sure it, also, is not shorting to the surrounding metal...

Let us know...

Just think it odd that both radios are doing the same thing---so think it might be possible that you are missing something obvious...

John


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Thu 01, 2018 4:56 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
I thought it odd that both radios exhibit the same problem too, but figured maybe there is a weak-link, a common failure mode for these radios?

I'm using a new antenna purchased just for this testing. It's a cheap one that has the rubber mast. I did check the center pin to connector shell and found not shorted. Also verified the center pin has continuity to the threaded stud where the antenna mast screws onto it, so the length of antenna wire seems okay. I am not grounding the antenna clamp mechanism, as would be when installed and clamped to the metal fender, but I don't think that matters?

I also plugged it in and checked to ensure the center pin made continuity with the metal socket inside the radio and also checked to ensure nothing was shorted to the case in the antenna socket area. All seems okay, but maybe I will try just a length of bare wire for a test and see if anything changes. I have some solid copper Romex 14-2 house wiring, so I can pull out the bare copper ground wire and use that if that seems okay. Is length critical?

Thanks for all the good ideas to try!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Thu 01, 2018 5:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 707
Location: Pasadena CA USA
I am a big fan of not just throwing parts in and hope for the best, of course one of the exceptions is old electrolytic capacitors. You changed these and are certain that the new caps are installed with correct polarity (right?). Why don't you measure the voltage on each pin of each transistor and post the results here.


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Thu 01, 2018 6:42 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Hello,
Yes, I was very careful to install the new replacement electrolytic caps with polarity correct. No explosions. However, in some cases I could not find exact-value replacements, but think I got close enough? I will post the cap value/voltage removed and the value/voltage of the replacement and seek opinions to see if I need to try harder for better matching.

I will try to take voltages on each leg of transistors too. I think they are all fairly accessible. I will measure from each leg to the case ground at legs labeled B, C & E on the Photofact schematic and post findings.

Thanks for the help. Stay tuned, please!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Fri 02, 2018 1:25 am 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Okay, here's the values of the old caps and the replacements I purchased online from All Electronics and installed, in both radios. I could not find all exact replacements, so I had to exceed old values in most cases. Does this seem okay or could this be causing a problem?

Radio #1 Electrolytic capacitors:
C1 = 1000MFD 16V replaced with 1000MFD 16V
C2 (3-in-one can) =
400MFD 16V replaced with 1000MFD 16V
100MFD 16V replaced with 100MFD 16V
600MFD 3V replaced with 1000MFD 16V
C3 = 2MFD 15V replaced with 10MFD 16V
C4 = 25MFD 6V replaced with 10MFD 16V


Radio #2 Electrolytic capacitors:
C1 = 250MFD 16V replaced with 330MFD 50V
C2 (3-in-one can) =
555MFD 16V replaced with 1000MFD 16V
100MFD 16V replaced with 100MFD 16V
260MFD 3V replaced with 330MFD 50V
C3 = 2MFD 15V replaced with 10MFD 16V
C4 = 25MFD 6V replaced with 10MFD 16V

I will measure the transistor outputs tomorrow and post those too.
Thanks to all for sharing your knowledge. I sure appreciate the help!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Fri 02, 2018 3:59 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Update - some progress made.

I decided to move my testing upstairs in the house where I can have more space and hang more of the wire and antenna out of a window. I've also had to switch from jumpers off the car battery to using my 6amp battery charger for the 12V power supply. Nothing else changed.

I tested radio #1 this morning on the new set-up, and I do get a constant humming sound from the speaker, PLUS I am able to pull-in one (only one) radio station that I can barely hear at full volume. Volume does increase a little bit if I hold the antenna mast or touch the center pin of the antenna socket. Does this provide any useful information on what is needed to improve reception and volume?

I will carefully re-flow the solder joints on the volume control to ensure good connections and forge ahead and test the transistor outputs and report.
I also plan to test radio #2 on the new set-up to see what it does.

Thanks all.


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Fri 02, 2018 4:04 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5561
Location: Indianapolis, IN
Did you check charger output ? They are typically not designed for use as power supplies and may be putting out too much voltage under the small load of radio and aren't adequately filtered which is reason for hum---could damage radio !


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Fri 02, 2018 4:13 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
I did measure output at 12V but if it's a bad idea I'll bring the car battery up there instead. Thanks!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Fri 02, 2018 5:21 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
Okay the battery charger as power supply was a bad idea. I've connected to the car battery now and the humming sound is gone.

I've also run a length of wire as an antenna instead of the rubber mast cheapo one. Reception is improved a bit.

Radio #1 now pulls-in about 8 stations across the dial, but the volume is still very low even with volume cranked full-up.
Radio #2 about the same except I can only pull-in one strong local station around midpoint on the dial.

Does the fact I now have some reception and some low volume output help narrow-down the suspect component(s) preventing higher volume?
If radio #1 were louder I'd be very happy with it!

Thanks!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Fri 02, 2018 9:42 pm 
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Joined: Feb Mon 26, 2018 10:09 pm
Posts: 24
I just measured the transistor voltages on radio #1. I'm focused on radio #1 because it does pull in some stations, just has really low volume.

So, all except two of the 6 transistors measured near spec. The two that measured off-spec (X4 & X5) each showed 0V on a leg that should have 3.6V. The parts list calls then the 1st AF amp and 2nd AF amp, so this sounds like it could possibly be the reason for low amplification. New ones are only $1.99 ea, so I'm planning to order and replace them and will post results. Hoping this does it!


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 Post subject: Re: 1966 AM radio repair - mustang
PostPosted: Mar Sat 03, 2018 1:42 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5561
Location: Indianapolis, IN
Could you scan or take a good pic of schematic and post it here so we can follow what you're looking at ? Would make it much easier to help...

I was concerned about the charger since I've seen them output 20+ volts unloaded...

Great that you now have decent reception on the one set---but am wondering if there is something other than transistors causing the voltage issue since both are showing it... But being in the audio stage makes sense... Have been hoping that Meade (MAG) would jump in since he's our resident car radio pro !

Have always liked the '65-'66 Mustangs and remember well when they were new---and as a kid, had ridden in convertibles of both years owned by people I knew. When I got my driver's license, an older friend let me drive the '65 which he kept through the years and restored for his son... I still have the factory spinner hubcap I got out of trash from a neighbor behind school who was repairing a wrecked '65 or '66 fastback in 1970... Man---those "car crazy" days...

John


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