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Old 3rd Jun 2023, 7:22 pm   #1
Michael Maurice
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Default Grundig R45 Receiver

There is a problem with this receiver in that the protection circuit is not operating. I have included in this post the service manual which shows how complicated it is.

It is not easy to service either, the board which has the protection circuit is at the bottom of the cabinet with two boards above it and no access from underneath.

My suspicions lie with the circuit around C33 and D601 which I suspect should produce a negative voltage at the emitter of T607. There is 0v at this point.

But where would this voltage which I presume is AC come from?

If you follow route 100 it goes to the base of T153 and T154. It also goes to route 18 and via route 18 it goes to D1009 and R1065,

But where does it get an ac signal that goes to C33 and D601?

I'm stuck

PS The file for the S/M is too big for the forum, you can get it here
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Old 4th Jun 2023, 1:33 pm   #2
Silvered_Mica
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Default Re: Grundig R45 Receiver

Looks like hifiengine won't allow hot linking,
I got this-

"System Message
The file appears to have been called from an unauthorized website
."
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Old 4th Jun 2023, 1:57 pm   #3
ms660
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Default Re: Grundig R45 Receiver

Manual download here (click on RECEIVER 40):

https://freeservicemanuals.info/en/s...IVER40/R45/50/

Lawrence.
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Old 4th Jun 2023, 2:11 pm   #4
ms660
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Default Re: Grundig R45 Receiver

Are the "b" switch contacts 2&3 making when switched on?

Lawrence.
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Old 4th Jun 2023, 9:06 pm   #5
Michael Maurice
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Default Re: Grundig R45 Receiver

Quote:
Originally Posted by ms660 View Post
Are the "b" switch contacts 2&3 making when switched on?

Lawrence.
Yes,

There is no 46V and there's no a/c voltage at either R639 or C633
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Old 5th Jun 2023, 7:27 pm   #6
frsimen
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Default Re: Grundig R45 Receiver

For the relay to pick up, the 46.5V supply from T609 is needed. T609 is an emitter follower, so its output will be 0.6V lower than the voltage on its base. The voltage at the base will either be about 47V or, if T608 is conducting, something much lower. the exact value being determined by T607.

The circuit feeding the emitter of T607 comes into play when the unit is switched off. The falling of the 55V supply will result in a negative going pulse on the emitter of T607, which will turn it on, turning off T608 and allowing T609s base and emitter voltages to rise to 47/46.5Volts.

It looks from this as if the relay is only powered under fault conditions, or at switch off.

Paula
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Old 5th Jun 2023, 7:37 pm   #7
Michael Maurice
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Default Re: Grundig R45 Receiver

Paula, I will check this out tomorrow, but when the unit is switched off, the relay is disconnected from the 46V by contacts on switch B.

When I first checked the unit out, there was no sound from the speakers.
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