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Old 9th May 2009, 5:49 pm   #141
stonehopper
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Default Re: Roberts RT7 - problem

Thought I would do that.
In the 200 Ohm range;
chassis to;
TR7 emitter - 3.7
TR6 emitter - 1 . (open circuit)

Negative battery lead to;
TR7 collector - 1.6
TR6 collector - 1.7

R30 - 122.6

R28 - no reading in the 200 Ohm range, but in the 2000 Ohm range - 375

Speaker wires in 200 Ohm - Black 1.1 Red 1.2

That smokey melted thing is not well after all!

Derek
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Old 9th May 2009, 6:31 pm   #142
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Default Re: Roberts RT7 - problem

Well at last we're getting somewhere.

Meter faulty on 20mA range. Not good for measuring current consumption.

R27 51 ohms off value at 80 ohms. Replaced with 47 ohms.

R28 270 ohms off value at 370 ohms. Doesn't matter much.

R30 measures 122.6 ohms. Can't pronounce judgemnet on this as don't know the correct value. Need to know its colour code.

T2 primary open circuit one half. This is a symptom of excess current through the transformer, but not the cause of it.

You need to source a new transformer, rewind it or get it rewound.

In the mean time I'll leave you to try out geofy's suggestion.
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Old 9th May 2009, 6:50 pm   #143
stonehopper
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Default Re: Roberts RT7 - problem

Quite so Graham!

By the way, the R30, whose value is obscured on the service sheet, has a code of Brown Black Brown Silver.

I think we ought to put this one to bed at this point. We have ascertained a faulty transformer, and I have learned a small amount about radios.

For the latter, I must thank you all for your patience in leading me by the hand, and I'm sure at some point quite ready to let me go!! Wouldn't have blamed anyone. So a big thanks of appreciation from me to all who have chipped in to get me sorted out.

I will have a look at Geof's solution, but with the probability that a new(er) transformer might be the best solution, I'll be on the hunt for one - or a comparable one in the future. I won't be getting rid of it, but might have to put it up on the shelf for a while and get back to some carpentry on the old boat which has been wondering where the devil I've been this last week or three!!

Once again - very many thanks to all.

Derek Reynolds.
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Old 9th May 2009, 7:04 pm   #144
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Default Re: Roberts RT7 - problem

Quote:
By the way, the R30, whose value is obscured on the service sheet, has a code of Brown Black Brown
That's 100 ohms.
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