Roberts R200
 

Hi I would like to repair my R200.
The symptoms are that it is very quiet and only just receives stations probably only two.
I do not have any knowledge of this radio but am able to disassemble and have good skills with a soldering iron.
Would you be able to take me through the repair steps?
Thanks for your kind help
peter

Re: Roberts R200
 

Start by cleaning all the switches - Servisol will do. Then see if the antenna coil has been disturbed.

Which version have you got? You can get all three versions in the one sheet up top there.

Check capacitors and also possibly the AM diode.

Cheers,

Steve P.

Re: Roberts R200
 

This could be the dreaded AF117 transistors 8-o
With the radio on,try giving them a tap, this will either restore volume or go off totally!
:beer:
Mark

Re: Roberts R200
 

Thanks Steve, I will get some servisol and give it a go.
Mark, I tried giving them a tap but no improvement. To be honest the reception has got worse.
I am not sure which exact model it is. There are three black and four silver transisters. It is hard to read them but it looks like OCR1
thanks both
Peter

Re: Roberts R200
 

If there's three black transistors it'll be the first version which, as it happens, is the more reliable one despite being the oldest. The black transistors will be OC44, OC45, OC45 and what you've interpreted as OCR1 will be OC81.

On LW and given your location you should be able to receive BBC R4 at 1500m (That point is marked "Light" on these radios) plus a couple of other weaker stations at each end of the scale. On MW you should be able to receive an abundance of stations across the scale and with varying clarity.

Do first as others have suggested; Servisol and check aerial coils haven't shifted. The latter should be fixed to the ferrite rod with wax or maybe a splash of paint. Re the Servisol, get a can of 'Super 10'. Apply it to the wavechanger and operate the switch several times immediately afterwards. Note that if you overdo the Servisol the radio may do weird things for a little while; it'll settle after a short time if it does.

To access the wavechanger you will need to remove the chassis to the extent permitted by the 'speaker wires. If you don't know how to do this, first remove the knobs, then the two wooden wedges, lower the chassis so the tuning scale leaves the aperture and then lift out the chassis. DO NOT pull the chassis out by tugging on the ferrite aerial, this is often a cause of damage. On this point, check to make sure the ferrite rod hasn't fractured but if it has it should be obvious.

Having Servisolled the wavechanger and, while you're at it, the volume control, tune to a decent station ('decent' meaning good signal) on both wavebands and see if it comes in at the correct point on the tuning scale (This is assuming the Servisol and aerial check hasn't cured the problem). If it does but the radio is still weak, there could be an IF alignment issue. If it doesn't, there could be an oscillator and general alignment issue.

Other possibilities include a faulty OC44 (rare but not unknown), an output stage fault or a fault with a small capacitor which lurks inside one of the IF cans.

There'll also be a few of those red+yellow Plessey electrolytics grinning at you from the chassis and these are known to give trouble with age. There'll be some Hunts capacitors too but, unlike in valved sets, they don't give too much trouble in transistorised efforts.

I note you thought tapping the transistors made things worse. Check for a dry joint at that particular transistor while the chassis is out.

Couple of other points before I buzz off; remember that ferrite rod aerials are directional and thus need to point towards the transmitter. Just rotate the radio on its turntable (if it's still present) until best reception is obtained.

The second pre-buzz off point is the battery; make sure it's up to the job and spitting out something approaching 9v on load. That is obvious, I know, but it's happened before in these forums.........every possible fault investigated, only to find out the battery was duff to begin with.

Hope that helps.

Re: Roberts R200
 

Also check the capacitors near the aerial input. get a 0.1 or similar and place across the contacts of the ones in situ. It may just burst into song and then you know which to change (personally I would do them all anyway)

Re: Roberts R200
 

Quick guess - C4.

Cheers,

Steve P.

Re: Roberts R200
 

This may be a silly question, but is the battery in good condition? I have one of these sets and it is not very tolerant of low battery volts.

Re: Roberts R200
 

ISTR that ferrite rod aerials need to be broadside to the transmitter, you get a null if the axis of the rod is pointing at the transmitter.

Of course, rotating the radio for best reception is still just as valid ;)

Chris