Golden Sovereign silent on AM - UK Vintage Radio Repair and Restoration Discussion Forum

wireful3 · 31st Oct 2008, 8:26 pm

Help!

I have a Golden Sovereign that is fantastic on FM but absolutely silent on AM.

I have the Hacker service sheets but have difficulty following the drawings.

Applying 470 KHz to the input of the IF module gives a very healthy output but otherwise the set is dead on AM. If I try to search for a signal from the local oscillator --nothing.

I guess the LO has failed but I can't find where to look for it. My first guess from the drawings is that it is on the switch unit but looking at the set I am not sure.

Can anyone help me??

Steve_P · 31st Oct 2008, 8:33 pm

With all Hackers, the first thing to do is clean the wavechange switch!

I have 3 diagrams for Sovereign, but none for Golden Sovereign. There should be an RP no - What is it?

Cheers,

Steve P.

Paul_RK · 31st Oct 2008, 9:07 pm

Quote:

Originally Posted by Steve_P

I have 3 diagrams for Sovereign, but none for Golden Sovereign. There should be an RP no - What is it?

RP722MB - electrically just the same as the RP72MB Sov. III.

Paul

wireful3 · 31st Oct 2008, 9:29 pm

Thanks Steve and Paul.

Yes it is RP72 MB,
I have given the switches one treatment with cleaner but I will have another go. The switches certainly control the HT correctly between AM and FM on the IF boards. I am not very hopeful as there is no noise at all when switching between LW and MW but I would feel foolish if I hadn't persevered.

Could it be an aerial coil fault ?

Station X · 31st Oct 2008, 9:48 pm

Have you tried the old trick of listening for the Local Oscillator on another receiver?

wireful3 · 1st Nov 2008, 9:50 am

Hi Graham,
Yes I tried that with no success. One ray of hope is that I had a closer look at the switch panel and think I have found that the LO transistor may be there. If so this might help as my data sheet gives some voltages for the transistor electrodes.

wireful3 · 2nd Nov 2008, 9:41 am

Thanks to all who helped.

I have solved my first difficulty and found that the LO transistor is in fact on the switch pcb. I have checked the emitter voltages against the service sheet and they seem fairly close but I still have no sound and no sign of radiation from the LO. If the emitter voltages are in spec can I assume that the transistors are getting the supplies to the other eectrodes and also that they are more or less working?

Station X · 2nd Nov 2008, 9:46 am

Could you post an extract from the circuit diagram showing the LO and mixer?

Paul_RK · 2nd Nov 2008, 12:20 pm

Here's the switch board carrying the AM front end components - this is for the original RP72 but I think the -MB is much the same.

Paul

wireful3 · 2nd Nov 2008, 12:44 pm

Thanks Paul.

I do hope it gives someone thoughts that might help. Incidentally applying modulated 470 KHz to the twisted pair at the tops gives satisfactory output, so from there on I think things are OK.

Station X · 2nd Nov 2008, 12:59 pm

I've tidyed the thread up a bit.

julie_m · 2nd Nov 2008, 1:09 pm

Quote:

Originally Posted by wireful3

Applying modulated 470 KHz to the twisted pair at the tops gives satisfactory output, so from there on I think things are OK.

Then, suspect the local oscillator and/or mixer. Have you an oscilloscope with enough bandwidth to see the LO frequency? Alternatively, it could be that the AGC transistor is short-circuit, but your signal generator has a low enough output impedance to get past it.

Station X · 2nd Nov 2008, 1:44 pm

Studying all the interconnections in the full manual makes my brain hurt!

I'd be inclined to check the voltage at point 'D' on the switch board (should be 6V) with the set switched to MW and then all the voltages aound TR1, comparing the readings with those in the manual. Check the resistor values around TR1 too and the continuity of L1 and all the coils on the ferrite rod.

wireful3 · 2nd Nov 2008, 3:56 pm

Hi Graham , My brain hurts too! I am using the copy of the Hacker Service Chart on Paul's DVD and it is hard work.
I made the measurements you suggested using a digital meter as I have no AVO 8.

Voltage at point D is 5.8v it is not the same as spec but it is present and responds to the FM/AM switching.

R3 is 1K as in the diagram But R1 and R2 are out
R1 is 6.8K not 10K and R2 is 5K not 6.8K
This would affect the base bias on TR1 but only a small amount.

I measured the dc voltages on TR! though I only found the emitter voltage to check.
These were:- base 2.2 volts emitter 1.5v which is correct and collector 5.6v.
An interesting point is that the actual base voltage is not far from that calculated for the voltage divider R1 and R2. I will see if I can find a scope to look around but I now suspect I have a coil problem.
Should I see LO at the collector of TR1?

Steve_P · 2nd Nov 2008, 6:46 pm

Try antenna coupling of 470 Khz rather than a direct connection, see if that gets through. If not, look at the IF module and AFC.

Put your meter on ohms across those coils at the top there and make sure they are OK.

If there's no local oscillator signal, check L1.

Don't think pieces of wire are blameless. Try a soldering session.

Check TC3.

Possibility - C1?

Cheers,

Steve P.

Station X · 2nd Nov 2008, 6:59 pm

Quote:

R3 is 1K as in the diagram But R1 and R2 are out
R1 is 6.8K not 10K and R2 is 5K not 6.8K
This would affect the base bias on TR1 but only a small amount.

When you say they are "out" do you mean that the wrong value has been fitted or that the resistors have drifted in value. If they've drifted they're now more than 20% off value. If so I'd change them as it's two less things to worry about. Remember that if you measure resistors in circuit you may get a false reading due to shunting by other components.

LO output should appear at the emitter and point 'P'. 'N' is the external aerial connection and 'M' the connection to the tuning capacitor.

wireful3 · 2nd Nov 2008, 8:03 pm

Looking at the resistors it seems the correct components were fitted. I measured the resistors in circuit so I assume that they have drifted in use.

I have just found something significant that means I will have to examine the coil L1. There was a small label stuck to it with initials S. A. on it written in biro, that I assumed was an inspector's mark. When I looked at it the other way up it could be U.S with a badly written U. The fact that the core protrudes from the can by an unusual amount is suspicious! I don't like working on coils because years ago I wrecked one trying to mend it but it looks as if I have tried all the easy things. I will check the coils on the ferrite rod first as I have some spares for this.

Wish me luck

wireful3 · 20th Nov 2008, 9:44 am

This is now singing away merrily on all bands and fortunately I did not have to cope with any coils.

I followed the advice given about common faults only to confirm everything was fine. The fault was the feed resistor to the 1st transistor in the IF amplifier. This looks like the mixer stage, so it explains why an input at the IF frequency gave a very strong output. It had gone very high in value, something I have not seen before with this style of resistor.

I might have misled myself earlier when giving components a quick check by misreading the value of this resistor. I used an auto-scale digital meter and because the numbers were right I didn't notice the "k" sign after them. (CARELESS)

It was worth all the effort because the set now sounds fine.

Mods, I think this thread can now be closed because it has been a success.

31st Oct 2008, 8:26 pm	#1
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Golden Sovereign silent on AM Help! I have a Golden Sovereign that is fantastic on FM but absolutely silent on AM. I have the Hacker service sheets but have difficulty following the drawings. Applying 470 KHz to the input of the IF module gives a very healthy output but otherwise the set is dead on AM. If I try to search for a signal from the local oscillator --nothing. I guess the LO has failed but I can't find where to look for it. My first guess from the drawings is that it is on the switch unit but looking at the set I am not sure. Can anyone help me??

31st Oct 2008, 8:33 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Golden Sovereign silent on AM With all Hackers, the first thing to do is clean the wavechange switch! I have 3 diagrams for Sovereign, but none for Golden Sovereign. There should be an RP no - What is it? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

31st Oct 2008, 9:29 pm	#4
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM Thanks Steve and Paul. Yes it is RP72 MB, I have given the switches one treatment with cleaner but I will have another go. The switches certainly control the HT correctly between AM and FM on the IF boards. I am not very hopeful as there is no noise at all when switching between LW and MW but I would feel foolish if I hadn't persevered. Could it be an aerial coil fault ?

31st Oct 2008, 9:48 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Golden Sovereign silent on AM Have you tried the old trick of listening for the Local Oscillator on another receiver? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

1st Nov 2008, 9:50 am	#6
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM Hi Graham, Yes I tried that with no success. One ray of hope is that I had a closer look at the switch panel and think I have found that the LO transistor may be there. If so this might help as my data sheet gives some voltages for the transistor electrodes.

2nd Nov 2008, 9:41 am	#7
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM Thanks to all who helped. I have solved my first difficulty and found that the LO transistor is in fact on the switch pcb. I have checked the emitter voltages against the service sheet and they seem fairly close but I still have no sound and no sign of radiation from the LO. If the emitter voltages are in spec can I assume that the transistors are getting the supplies to the other eectrodes and also that they are more or less working?

2nd Nov 2008, 9:46 am	#8
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Golden Sovereign silent on AM Could you post an extract from the circuit diagram showing the LO and mixer? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

2nd Nov 2008, 12:20 pm	#9
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,259	Re: Golden Sovereign silent on AM Here's the switch board carrying the AM front end components - this is for the original RP72 but I think the -MB is much the same. Paul Attached Thumbnails

2nd Nov 2008, 12:44 pm	#10
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM Thanks Paul. I do hope it gives someone thoughts that might help. Incidentally applying modulated 470 KHz to the twisted pair at the tops gives satisfactory output, so from there on I think things are OK.

2nd Nov 2008, 12:59 pm	#11
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Golden Sovereign silent on AM I've tidyed the thread up a bit. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

2nd Nov 2008, 1:44 pm	#13
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Golden Sovereign silent on AM Studying all the interconnections in the full manual makes my brain hurt! I'd be inclined to check the voltage at point 'D' on the switch board (should be 6V) with the set switched to MW and then all the voltages aound TR1, comparing the readings with those in the manual. Check the resistor values around TR1 too and the continuity of L1 and all the coils on the ferrite rod. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

2nd Nov 2008, 3:56 pm	#14
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM Hi Graham , My brain hurts too! I am using the copy of the Hacker Service Chart on Paul's DVD and it is hard work. I made the measurements you suggested using a digital meter as I have no AVO 8. Voltage at point D is 5.8v it is not the same as spec but it is present and responds to the FM/AM switching. R3 is 1K as in the diagram But R1 and R2 are out R1 is 6.8K not 10K and R2 is 5K not 6.8K This would affect the base bias on TR1 but only a small amount. I measured the dc voltages on TR! though I only found the emitter voltage to check. These were:- base 2.2 volts emitter 1.5v which is correct and collector 5.6v. An interesting point is that the actual base voltage is not far from that calculated for the voltage divider R1 and R2. I will see if I can find a scope to look around but I now suspect I have a coil problem. Should I see LO at the collector of TR1?

2nd Nov 2008, 6:46 pm	#15
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Golden Sovereign silent on AM Try antenna coupling of 470 Khz rather than a direct connection, see if that gets through. If not, look at the IF module and AFC. Put your meter on ohms across those coils at the top there and make sure they are OK. If there's no local oscillator signal, check L1. Don't think pieces of wire are blameless. Try a soldering session. Check TC3. Possibility - C1? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

2nd Nov 2008, 8:03 pm	#17
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM Looking at the resistors it seems the correct components were fitted. I measured the resistors in circuit so I assume that they have drifted in use. I have just found something significant that means I will have to examine the coil L1. There was a small label stuck to it with initials S. A. on it written in biro, that I assumed was an inspector's mark. When I looked at it the other way up it could be U.S with a badly written U. The fact that the core protrudes from the can by an unusual amount is suspicious! I don't like working on coils because years ago I wrecked one trying to mend it but it looks as if I have tried all the easy things. I will check the coils on the ferrite rod first as I have some spares for this. Wish me luck

20th Nov 2008, 9:44 am	#18
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Golden Sovereign silent on AM This is now singing away merrily on all bands and fortunately I did not have to cope with any coils. I followed the advice given about common faults only to confirm everything was fine. The fault was the feed resistor to the 1st transistor in the IF amplifier. This looks like the mixer stage, so it explains why an input at the IF frequency gave a very strong output. It had gone very high in value, something I have not seen before with this style of resistor. I might have misled myself earlier when giving components a quick check by misreading the value of this resistor. I used an auto-scale digital meter and because the numbers were right I didn't notice the "k" sign after them. (CARELESS) It was worth all the effort because the set now sounds fine. Mods, I think this thread can now be closed because it has been a success.