Thread: Roberts R200
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Old 15th Oct 2009, 12:13 am   #5
Darren-UK
Retired Dormant Member
 
Join Date: Apr 2003
Location: Blackpool, Lancashire, UK.
Posts: 4,061
Default 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.
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