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Seek advice on Marantz 1180 Dc amplifier high DC out put at left speaker channel

lwong2's picture

Does anyone has the marantz 1180 DC -- please help me to confirm my doubt on the circuit.

My amp has the transistor Q854 removed.In its place at the collector (C) point is soldered a 51 ohm resistor connected in series to a diode RM 11 and a capacitor shorting to a runner. -- is this normal. I m not the first owner of this amp.

My amp has a +ve 45 V supply and a -ve supply of 53 V . Both shd be 45 V.

The dc out put at the left channel adjusted lowest to ,is 3.8 V while thr rt channel is OK.
When the amp is powered on the left speaker is being pushed outward and stay on.

I hv checked out all resistors and transistors at the main amp board, comparing value between left and right channels. They are all OK ,except resistor R725 (lt channel) is
1512 ohm and R 726 at (rt ch) is 5740 ohm when measured on board. But when desoldered and measure, both the resistor measure 22K ohm -- which are Ok.

Can someone kindly help me with this problem

Thank you



Re: Seek advice on Marantz 1180 Dc amplifier high DC out put ...

As told by previous poster, get your plus-minus 45 volt supply fixed, as for the in circuit measurements,it seems as though your trim-pot R-739 (22k) is stuck on one end of its travel and you are measuring r723(1k) in series with r737(560ohm) these two would be in parallel with 22k ohm (r7250). If trim-pot is stuck to one side, it would cause your dc offset problem at your speaker. Put r725 back in circuit because it is good and measure resistance while you turn trim-pot R-739, resistance should change, if not you have bad trim-pot for starters. There may be more bad but these are good starting points. One more thing, please disconnect your speakers until amp is fixed, they don't like dc.

sbrservice's picture

Re: Seek advice on Marantz 1180 Dc amplifier high DC out put ...

totally abnormal ...
Check circuit behind rectifier and check caps

Re: Seek advice on Marantz 1180 Dc amplifier high DC out put ...

There should be a Q854; it is the negative 45 volt regulator. I'm a little surprised your protection circuit is allowing any output; you need to replace that regulator and any other parts that have been removed, then check your protection circuit--it may have been modified or disabled.