Motorola car radio - UK Vintage Radio Repair and Restoration Discussion Forum

Mike Bennett · 15th Dec 2019, 8:41 am

Hi
I am new to the forum and maybe should not be here!
I am looking for help with diagnosing why my 1970’s Motorola 184 car radio.
It powers up giving the panel light, there is impedance on the speaker output but nothing else.
Any guidance would be appreciated
I apologise if I am in the wrong place
Thanks
Mike

'LIVEWIRE?' · 15th Dec 2019, 12:08 pm

Despite having worked for an auto-electrical firm for over 23 years as their I.C.E> (Car Stereo) Service Engineer, I can't place a model 184, unless it's the somewhat rare AM/FM model. In the early 70s the Motorola Radios, identical to Radiomobile sets, were the 727 & 828 (same as Rdm 170 & 1080) All were MW/LW Push-button Radios. Later Motorola produced their own range, the 112.114, 122 & 124, again MW/LW in Stotfold, Herts.. However, there are several things which could cause this problem - the first being, and sorry if I'm stating the obvious, this is likely to be a 12volt Negative Earth only radio. Other than that it's possible that there is a fault in the audio output stages, and checks inside, with a multimeter set to a lowish (25 or 30vFSD) DC volts range, would be needed. A 'buzz' test at the volume control would prove whether or not the output syages are working. Another possibility, although I don't recall Motorola Radios ever having 'tape' sockets factory fitted, is that a blanking plug is un plugged or missing. This would mute the radio. Perhaps you can post picture(s) of the radio, including one clearly showing the model No. to help us positively identify it.

Reelman · 15th Dec 2019, 1:40 pm

A quick search provided this picture of a 184 courtesy of eBay. A similar model was the subject of this thread.....

https://www.vintage-radio.net/forum/...d.php?t=125651

Good luck with it!
Peter

'LIVEWIRE?' · 15th Dec 2019, 1:56 pm

I only ever saw those badged as BL or Austin-Rover, etc., so never knew the Motorola Model Number. IIRC they used a TDA2002 or 2003 as the audio amplifier. Despite being supposedly 'bomb-proof ' , they did sometimes fail. Checking for sound at the top of the volume control, plus a visual inspection of the o/p IC would still be a good starting point. These were definitely Negative earth only.

Mike Bennett · 16th Dec 2019, 6:59 pm

Thanks Gentlemen, yes negative earth. I actually have 2 of these, one Motorola 184 with a plain front panel. It was suggested that this was an MG radio. The second is a BL version badged for Rover and has a fly lead for power antenna.
Both are in the same state of disrepair !

Station X · 17th Dec 2019, 12:56 pm

Quote:

Originally Posted by Mike Bennett

there is impedance on the speaker output but nothing else.

What exactly do you mean by that?

HamishBoxer · 17th Dec 2019, 1:54 pm

Sounds like someone has put an Ohms meter across the output stage (speaker leads).Not ideal.

'LIVEWIRE?' · 17th Dec 2019, 2:13 pm

Not if the radio was switched on at the time, HB, although there is a speaker coupling cap (470 or 1000uf from memory), so no DC (Unless said cap is faulty) should be present across the speaker.

cheerfulcharlie · 17th Dec 2019, 2:28 pm

Can you post some pictures with the cover plates off.

Somebody here might get an idea of what is going on

Mike Bennett · 18th Dec 2019, 3:03 pm

Picture of 184 innards attached.

Yes I put an ohm meter across the speaker cables, seemed a good idea at the time. Only after a test with antenna and speakers failed to give any output

'LIVEWIRE?' · 18th Dec 2019, 10:35 pm

Putting an ohm meter across the speaker cables is perfectly OK as long as the radio is switched off and preferably disconnected from the supply when this is done. If no speaker is connected, and the meter's negative terminal connected to the speaker negative lead (which should be common with the radio chassis ), with meter positive to the other speaker lead, the speaker coupling capacitor will charge via the ohm meter so that an open circuit reading will result. Your picture appears to be a different model to the one in my mind, but I assume the device on the heatsink at the top of the photo is the output IC, from which a 470 or 1000uf capacitor connects to the speaker lead.

Mike Bennett · 20th Dec 2019, 8:35 am

It’s 1000uF and it seems to be open circuit.

'LIVEWIRE?' · 20th Dec 2019, 12:47 pm

If the coupling cap is O/C, that may be the only fault. Check that there is approx. half supply (between ca. 5.5 & 7v) on the coupling cap. positive side. If so either bridge to coupling cap with a known good 1000uf electrolytic, or simply replace it. In my experience they don't often fail o/c. though I have known them fail s/c in any make & model of radio, but it's easy to change the capacitor, which may be the only fault.

Mike Bennett · 23rd Dec 2019, 12:45 pm

Thanks for that, It seems to read 10-12 volt (with the radio connects to 12v supply)

'LIVEWIRE?' · 23rd Dec 2019, 7:38 pm

This suggests to me that there is a fault in the output stage, since, in all car radio audio amplifiers, other than single-ended circuits, I've ever known about, the +ve side of the speaker coupling capacitor should be at approx. half the supply voltage, w.r.t the negative line. The output I.C., which is probably a TDA2002 or 2003, is almost certainly faulty.

15th Dec 2019, 8:41 am	#1
Mike Bennett Retired Dormant Member Join Date: Dec 2019 Location: Northumberland, UK. Posts: 5	Motorola car radio Hi I am new to the forum and maybe should not be here! I am looking for help with diagnosing why my 1970’s Motorola 184 car radio. It powers up giving the panel light, there is impedance on the speaker output but nothing else. Any guidance would be appreciated I apologise if I am in the wrong place Thanks Mike

15th Dec 2019, 12:08 pm	#2
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Motorola car radio Despite having worked for an auto-electrical firm for over 23 years as their I.C.E> (Car Stereo) Service Engineer, I can't place a model 184, unless it's the somewhat rare AM/FM model. In the early 70s the Motorola Radios, identical to Radiomobile sets, were the 727 & 828 (same as Rdm 170 & 1080) All were MW/LW Push-button Radios. Later Motorola produced their own range, the 112.114, 122 & 124, again MW/LW in Stotfold, Herts.. However, there are several things which could cause this problem - the first being, and sorry if I'm stating the obvious, this is likely to be a 12volt Negative Earth only radio. Other than that it's possible that there is a fault in the audio output stages, and checks inside, with a multimeter set to a lowish (25 or 30vFSD) DC volts range, would be needed. A 'buzz' test at the volume control would prove whether or not the output syages are working. Another possibility, although I don't recall Motorola Radios ever having 'tape' sockets factory fitted, is that a blanking plug is un plugged or missing. This would mute the radio. Perhaps you can post picture(s) of the radio, including one clearly showing the model No. to help us positively identify it.

15th Dec 2019, 1:40 pm	#3
Reelman Octode Join Date: Aug 2008 Location: Rotherham, South Yorkshire, UK. Posts: 1,723	Re: Motorola car radio A quick search provided this picture of a 184 courtesy of eBay. A similar model was the subject of this thread..... https://www.vintage-radio.net/forum/...d.php?t=125651 Good luck with it! Peter Attached Thumbnails

15th Dec 2019, 1:56 pm	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Motorola car radio I only ever saw those badged as BL or Austin-Rover, etc., so never knew the Motorola Model Number. IIRC they used a TDA2002 or 2003 as the audio amplifier. Despite being supposedly 'bomb-proof ' , they did sometimes fail. Checking for sound at the top of the volume control, plus a visual inspection of the o/p IC would still be a good starting point. These were definitely Negative earth only.

16th Dec 2019, 6:59 pm	#5
Mike Bennett Retired Dormant Member Join Date: Dec 2019 Location: Northumberland, UK. Posts: 5	Re: Motorola car radio Thanks Gentlemen, yes negative earth. I actually have 2 of these, one Motorola 184 with a plain front panel. It was suggested that this was an MG radio. The second is a BL version badged for Rover and has a fly lead for power antenna. Both are in the same state of disrepair ! Attached Thumbnails

17th Dec 2019, 1:54 pm	#7
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Motorola car radio Sounds like someone has put an Ohms meter across the output stage (speaker leads).Not ideal. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

17th Dec 2019, 2:13 pm	#8
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Motorola car radio Not if the radio was switched on at the time, HB, although there is a speaker coupling cap (470 or 1000uf from memory), so no DC (Unless said cap is faulty) should be present across the speaker.

17th Dec 2019, 2:28 pm	#9
cheerfulcharlie Heptode Join Date: May 2009 Location: Birmingham, West Midlands, UK. Posts: 708	Re: Motorola car radio Can you post some pictures with the cover plates off. Somebody here might get an idea of what is going on

18th Dec 2019, 3:03 pm	#10
Mike Bennett Retired Dormant Member Join Date: Dec 2019 Location: Northumberland, UK. Posts: 5	Picture of 184 innards attached. Yes I put an ohm meter across the speaker cables, seemed a good idea at the time. Only after a test with antenna and speakers failed to give any output Attached Thumbnails

18th Dec 2019, 10:35 pm	#11
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Motorola car radio Putting an ohm meter across the speaker cables is perfectly OK as long as the radio is switched off and preferably disconnected from the supply when this is done. If no speaker is connected, and the meter's negative terminal connected to the speaker negative lead (which should be common with the radio chassis ), with meter positive to the other speaker lead, the speaker coupling capacitor will charge via the ohm meter so that an open circuit reading will result. Your picture appears to be a different model to the one in my mind, but I assume the device on the heatsink at the top of the photo is the output IC, from which a 470 or 1000uf capacitor connects to the speaker lead.

20th Dec 2019, 8:35 am	#12
Mike Bennett Retired Dormant Member Join Date: Dec 2019 Location: Northumberland, UK. Posts: 5	Re: Motorola car radio It’s 1000uF and it seems to be open circuit.

20th Dec 2019, 12:47 pm	#13
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Motorola car radio If the coupling cap is O/C, that may be the only fault. Check that there is approx. half supply (between ca. 5.5 & 7v) on the coupling cap. positive side. If so either bridge to coupling cap with a known good 1000uf electrolytic, or simply replace it. In my experience they don't often fail o/c. though I have known them fail s/c in any make & model of radio, but it's easy to change the capacitor, which may be the only fault.

23rd Dec 2019, 12:45 pm	#14
Mike Bennett Retired Dormant Member Join Date: Dec 2019 Location: Northumberland, UK. Posts: 5	Re: Motorola car radio Thanks for that, It seems to read 10-12 volt (with the radio connects to 12v supply)

23rd Dec 2019, 7:38 pm	#15
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Motorola car radio This suggests to me that there is a fault in the output stage, since, in all car radio audio amplifiers, other than single-ended circuits, I've ever known about, the +ve side of the speaker coupling capacitor should be at approx. half the supply voltage, w.r.t the negative line. The output I.C., which is probably a TDA2002 or 2003, is almost certainly faulty.