Roberts R200 - UK Vintage Radio Repair and Restoration Discussion Forum

Johnbarn · 20th Mar 2017, 1:32 pm

I have recently inherited a very tatty green R200, knobs and handle missing, case missing catch ect. Serial Number 20298. It is the OC44/45/81D/81 series and I have the Trader sheets for it, 1449 and 1602. On initial switch on there was no sound but on inspecting the pcb I found a corroded and broken track round the perimeter. I bridged this and there was sound, but quite faint. On closer inspection I see that the L6/7/8 core is broken and at some time in the past someone else has bridged another piece of the pcb track. I have cleaned the wave change switch and it is working fine with good contact on all pads. If I connect a simple length of wire as an aerial to the orange wire at L4 on the ferrite rod I can get more volume on Radio 5 and a few other stations as well but without this wire it is very deaf. I have inspected everywhere on the aerial windings and all look remarkably sound; the voltages on the six transistors are in line with the Trader sheet figures and the wave change switch is good. The broken core is still adjustable and does alter the signal volume as expected. Has anyone any ideas where to look next?

ms660 · 20th Mar 2017, 1:40 pm

Could be an alignment job.

Lawrence.

GeoffK · 20th Mar 2017, 1:59 pm

A broken core in the oscillator windings is going to affect its ability to tune the coils correctly. Have the other cores been moved. Check C2 and C9 for correct adjustment, and L4 for best place on the ferrite rod.

Johnbarn · 20th Mar 2017, 2:41 pm

Thanks for those comments Geoff and Lawrence. If it's an alignment prob can this be done without sig generators of some kind? (I don't have any) And would the 3/4 core that's left in the osc section not tune the coils correctly? It is currently positioned for max volume. Where could I get a replacement? The other cores are sitting quite high but don't appear to have been moved. C2 and C9 behave as expected and are peaked for max signal. All the windings on the ferrite rod look as though they are in the original waxed positions.

GeoffK · 20th Mar 2017, 5:19 pm

John, if the IF cores don't look disturbed it is best to leave them, they can break easily if they can't move freely. The cores are usually just below or on the surface. A signal generator doesn't have to used, just turning the cores for maximum output and comparing station positions with another radio is one way. The oscillator core could affect the volume of output if the coil isn't being peaked. Another possibility is a weak oscillator transistor or L4 making poor connection.

ronbryan · 20th Mar 2017, 5:34 pm

Does it have those brown DCC (Dubilier) decoupling capacitors fitted?

Ron

Johnbarn · 20th Mar 2017, 6:27 pm

Thanks Geoff, the other cores look about right so I'll leave them alone but I'll check L4 joints and possibly exchange the OC44. As for the capacitors yes Ron there are 4 of the brown types but I can't see the manufacture's name. The electrolytics are all Plessey with the yellow tape labels.

ronbryan · 20th Mar 2017, 7:07 pm

John

Poor performance (deafness) on an R200 can be caused by those DCC brown capacitors as leakage on the emitter decouplers can tend to bias the IF transistors off. I would change them for 250V Vishays. The AGC decoupler, a 10uF Plessey electrolytic should also be checked.

Ron

GeoffK · 20th Mar 2017, 8:28 pm

Though as TR1 is oscillating it is probably ok so leave until capacitors have been looked at, and the coupling of the aerial coils, check the switch contacts again. It isn't helping that the oscillator core is damaged, this should be replaced first if one can be found.

Johnbarn · 25th Mar 2017, 1:54 pm

Roberts r200
i don't know if this should be a new thread or a continuation of the last one but i have now now replaced all the brown dcc capacitors and the plessey electrolytics, and even the diode x1. The results are still the same - with a short aerial connected to l2/l4 i have good volume but without it practically nothing. In desparation i have even removed the wavechange switch and connected the mw wave wires directly to where they should be with identical results. I have never worked on such an uncoopeative radio. Thanks to geoff, ron and lawrence for the help so far - has anyone any more ideas?

ms660 · 25th Mar 2017, 2:03 pm

That suggests that the junction of L2 and L4 might not be grounded to the rest of the circuit when switched to MW ?

Lawrence.

ms660 · 25th Mar 2017, 2:28 pm

Quote:

Originally Posted by Johnbarn

with a short aerial connected to l2/l4 i have good volume but without it practically nothing.

Just to clarify, do you mean the junction of L2 and L4 (the bottom ends as viewed in the schematic) or the top end of either L2 or L4?

Lawrence.

Johnbarn · 25th Mar 2017, 2:58 pm

It's the (orange) wire, top end of L2 which gives me a strong output when the wire aerial is connected to it. The wire also goes to C1/2.

ms660 · 25th Mar 2017, 3:04 pm

Does adjusting C2 result in a peak in the signal or noise at the HF end of the MW band, first with your temp short antenna then without the temp antenna?

Lawrence.

GeoffK · 25th Mar 2017, 4:36 pm

If you get sound when a wire is connected to L2/L4 then the oscillator, IF and detector diode X1 must have been working, X1 should have been left as this isn't the area where the fault is. As the fault appears to be around L2 L4 and the tuner this needs to be examined more closely, is the coil L2 intact, are the connections to the tuner intact, is the tuner making a good connection to its solder tags both inside and outside the tuner.

Johnbarn · 29th Mar 2017, 10:32 am

Thanks to everyone's comments and helpful suggestions I now have a working R200. It's not brilliant but works well enough on both MW and LW. Volume pot needs to be about 30/40% for listening comfort but it's good enough to listen to. Tone is good and the stations are coming in in the right places on the scale (Why is Radio 5 Live so loud?! Is it the same throughout the UK or only Northern ireland?) I can't say there was one thing that made the difference but replacing all the DCC and electrolytic capacitors certainly seemed to gradually improve things and I replaced three of the low value resistors R12,13,17 as well. The pcb tracks were retouched with new solder in this process but I really couldn't say that I found any dry joints. Alignment on a weak station, with the ferrite rod positioned to give min volume, was then done and the trimmers adjusted to position R4 correctly on the tuning scale. I now need to keep a lookout for replacement knobs and a green carrying handle.
On a general comment, this Roberts radio is a real nightmare of higgildipigildy wiring and pcb layout, are they all like that? With a Hacker you can at least follow the wiring through systematically. How come Roberts got the Royal Warrant and Hacker didn't?
Thanks to everyone for the help.

20th Mar 2017, 1:32 pm	#1
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Roberts R200 I have recently inherited a very tatty green R200, knobs and handle missing, case missing catch ect. Serial Number 20298. It is the OC44/45/81D/81 series and I have the Trader sheets for it, 1449 and 1602. On initial switch on there was no sound but on inspecting the pcb I found a corroded and broken track round the perimeter. I bridged this and there was sound, but quite faint. On closer inspection I see that the L6/7/8 core is broken and at some time in the past someone else has bridged another piece of the pcb track. I have cleaned the wave change switch and it is working fine with good contact on all pads. If I connect a simple length of wire as an aerial to the orange wire at L4 on the ferrite rod I can get more volume on Radio 5 and a few other stations as well but without this wire it is very deaf. I have inspected everywhere on the aerial windings and all look remarkably sound; the voltages on the six transistors are in line with the Trader sheet figures and the wave change switch is good. The broken core is still adjustable and does alter the signal volume as expected. Has anyone any ideas where to look next?

20th Mar 2017, 1:40 pm	#2
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Roberts R200 Could be an alignment job. Lawrence.

20th Mar 2017, 1:59 pm	#3
GeoffK Heptode Join Date: Mar 2016 Location: Essex, UK. Posts: 602	Re: Roberts R200 A broken core in the oscillator windings is going to affect its ability to tune the coils correctly. Have the other cores been moved. Check C2 and C9 for correct adjustment, and L4 for best place on the ferrite rod. __________________ *Geoff*

20th Mar 2017, 2:41 pm	#4
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Re: Roberts R200 Thanks for those comments Geoff and Lawrence. If it's an alignment prob can this be done without sig generators of some kind? (I don't have any) And would the 3/4 core that's left in the osc section not tune the coils correctly? It is currently positioned for max volume. Where could I get a replacement? The other cores are sitting quite high but don't appear to have been moved. C2 and C9 behave as expected and are peaked for max signal. All the windings on the ferrite rod look as though they are in the original waxed positions.

20th Mar 2017, 5:19 pm	#5
GeoffK Heptode Join Date: Mar 2016 Location: Essex, UK. Posts: 602	Re: Roberts R200 John, if the IF cores don't look disturbed it is best to leave them, they can break easily if they can't move freely. The cores are usually just below or on the surface. A signal generator doesn't have to used, just turning the cores for maximum output and comparing station positions with another radio is one way. The oscillator core could affect the volume of output if the coil isn't being peaked. Another possibility is a weak oscillator transistor or L4 making poor connection. __________________ *Geoff*

20th Mar 2017, 5:34 pm	#6
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Roberts R200 Does it have those brown DCC (Dubilier) decoupling capacitors fitted? Ron

20th Mar 2017, 6:27 pm	#7
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Re: Roberts R200 Thanks Geoff, the other cores look about right so I'll leave them alone but I'll check L4 joints and possibly exchange the OC44. As for the capacitors yes Ron there are 4 of the brown types but I can't see the manufacture's name. The electrolytics are all Plessey with the yellow tape labels.

20th Mar 2017, 7:07 pm	#8
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Roberts R200 John Poor performance (deafness) on an R200 can be caused by those DCC brown capacitors as leakage on the emitter decouplers can tend to bias the IF transistors off. I would change them for 250V Vishays. The AGC decoupler, a 10uF Plessey electrolytic should also be checked. Ron

20th Mar 2017, 8:28 pm	#9
GeoffK Heptode Join Date: Mar 2016 Location: Essex, UK. Posts: 602	Re: Roberts R200 Though as TR1 is oscillating it is probably ok so leave until capacitors have been looked at, and the coupling of the aerial coils, check the switch contacts again. It isn't helping that the oscillator core is damaged, this should be replaced first if one can be found. __________________ *Geoff*

25th Mar 2017, 1:54 pm	#10
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Re: Roberts R200 Roberts r200 i don't know if this should be a new thread or a continuation of the last one but i have now now replaced all the brown dcc capacitors and the plessey electrolytics, and even the diode x1. The results are still the same - with a short aerial connected to l2/l4 i have good volume but without it practically nothing. In desparation i have even removed the wavechange switch and connected the mw wave wires directly to where they should be with identical results. I have never worked on such an uncoopeative radio. Thanks to geoff, ron and lawrence for the help so far - has anyone any more ideas?

25th Mar 2017, 2:03 pm	#11
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Roberts R200 That suggests that the junction of L2 and L4 might not be grounded to the rest of the circuit when switched to MW ? Lawrence.

25th Mar 2017, 2:58 pm	#13
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Re: Roberts R200 It's the (orange) wire, top end of L2 which gives me a strong output when the wire aerial is connected to it. The wire also goes to C1/2.

25th Mar 2017, 3:04 pm	#14
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Roberts R200 Does adjusting C2 result in a peak in the signal or noise at the HF end of the MW band, first with your temp short antenna then without the temp antenna? Lawrence.

25th Mar 2017, 4:36 pm	#15
GeoffK Heptode Join Date: Mar 2016 Location: Essex, UK. Posts: 602	Re: Roberts R200 If you get sound when a wire is connected to L2/L4 then the oscillator, IF and detector diode X1 must have been working, X1 should have been left as this isn't the area where the fault is. As the fault appears to be around L2 L4 and the tuner this needs to be examined more closely, is the coil L2 intact, are the connections to the tuner intact, is the tuner making a good connection to its solder tags both inside and outside the tuner. __________________ *Geoff*

29th Mar 2017, 10:32 am	#16
Johnbarn Pentode Join Date: Feb 2015 Location: Belfast, Northern Ireland, UK. Posts: 130	Re: Roberts R200 Thanks to everyone's comments and helpful suggestions I now have a working R200. It's not brilliant but works well enough on both MW and LW. Volume pot needs to be about 30/40% for listening comfort but it's good enough to listen to. Tone is good and the stations are coming in in the right places on the scale (Why is Radio 5 Live so loud?! Is it the same throughout the UK or only Northern ireland?) I can't say there was one thing that made the difference but replacing all the DCC and electrolytic capacitors certainly seemed to gradually improve things and I replaced three of the low value resistors R12,13,17 as well. The pcb tracks were retouched with new solder in this process but I really couldn't say that I found any dry joints. Alignment on a weak station, with the ferrite rod positioned to give min volume, was then done and the trimmers adjusted to position R4 correctly on the tuning scale. I now need to keep a lookout for replacement knobs and a green carrying handle. On a general comment, this Roberts radio is a real nightmare of higgildipigildy wiring and pcb layout, are they all like that? With a Hacker you can at least follow the wiring through systematically. How come Roberts got the Royal Warrant and Hacker didn't? Thanks to everyone for the help.