Marantz 1180DC Relay? Problem, HELP

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Hello,
I bought a non working Marantz 1180DC thinking I could fix it. The previous owner said the relay was taking more time to click on. I removed the relay cover and cleaned the contacts, no result. I cleaned the contacts with 1000 sandpaper and again cleaned the contacts, no result. I re-melted the solder connections on the relay, no result. I also tried cleaning the selector switch, no result.

I can get the unit to work if I manually push the contacts on the relay in. The relay disengages properly when I turn the unit off.

Any Clues on how to fix this? There must be some function that engages the main relay that is bad or perhaps the relay itself is bad.
Where could I find a replacement relay?
Any suggestions would be great.

Opinions on this unit (if bad you will not hurt my feelings) are welcome as well. The 1180DC like an unusual design with the majority of the pc boards having the component side facing down. Would this cause over-heating problems?

Thanks so much,
Bruce
 
DC Detection Circuit or Power On Circuit?

Bruce,

Although I'am not familiar with your particular model I may be able to give you some hints.

The circuitry that operates most of these relays is a circuit that detects the presense of a DC voltage on the output of the power amplifier stages in the unit. This relay is used to protect speakers from damage cuased by applying A DC voltage to them.

Thus I suspect that there is such a voltage present. You can measure this with a dc voltmeter from the proper relay contact to ground. There is also likely to be a small inductor near the output stages from which you can also measure it.

If you ar lucky there are DC offset adjustments on both channels that may need to be adjusted. If there are not there is likely a problem with one or more of the components in the circuits. The first step is to find out which channel/channels are causing this problem. If there is no DC on one or both of the outputs the problem could be with the relay driver or associated circuit.

I have also seen amplifiers in which the DC protection circuit is powered by its own power supply. This however is rare. I would not force the relay to close with loudspeakers hooked up. If there is a DC voltage there it may damage your woofers gradually or even immediately.

There is also a posibility that the relay is a power on relay. These are usually controlled by a microprocceser and the relay itself is powered by small separate power supply. I don't know which of these posibilities apply to your unit.

There is of course also a possibilty that the relay coil is open. I would also check to see if the unit has any fuses in the main DC supply lines. Some of the spring contacs holding the fuses in could have lost tension and cause a bad connection.

John Fassotte
Alaskan Audio

[Edited by alaskanaudio on 12-04-2001 at 10:03 AM]
 
Bruce, I have repaired many amps with these symptoms and concur with John. The good news is that the repair is usually cheap.

The first thing you need to determine is whether the relay is pulling in and you're getting no output, or whether the relay is not pulling in at all or after a long time.

If the relays is pulling in then you need to check for bad contacts, soldering joints or loose wiring, basically a bad connection somewhere.

If it is not pulling in then in my experience common causes are:
Dry contact on DC offset pot, if your amp uses one, some have DC feedback instead, this usually applies to DC amps only.
If the amp is more than 10 years old, faulty electrolytic capacitors anywhere from the power supplies to the output stage. I change all electros in my gear as a matter of course after about 10 years, (don’t replace the large/expensive caps
Power supply imbalances, check that the power supply’s voltages are on spec.
Hot or dry joints on the amp PCB, have a good look under a strong light.
If the amp might have been over driven or has flat metal film resistors check then, particularly high values. Check also for discolouration of other components.
Semiconductor problems, transistors that have lost gain or have gone leaky. I have also found faulty double diodes, (biasing diodes).
There are of course other failures but these have been the most common.

Sorry that I can’t be more specific, as I’m not familiar with your amp. If you want more help please include any details and symptoms that you can.

Good luck.
Regards WALKER
 
Bruce,

.... check DC-offset first off all:

Connect DVM to JN01 and JN05 (Ground) and adjust left channel R739 until the meter indication reaches 0 mV (+- 5mV). Similarly, connect DVM to JN04 and JN06 (or Ground) and adjust right channel R740 as above.

You can also have a look at the schematic of the protection circuit i´ve mailed you today.

IMHO these 11xxDC amps from Marantz are worth to love them. I´ve got an 3250B preamp (some dusty switches), 1122DC (preamp not working) and the nice 1180DC (everything seems to be ok) last weeks. Having the service manuals I like to give them a few new components (caps) - hoping they´ll sound as 25 years ago after that!

When I´m back in the office next week I can sent copys of manual if you give me your postal address.

good luck and happy holidays

Det
 
Check for DC on the outputs by measuring this at the relay contacts. If there is no DC, check the resistance of the relay coil (you may have to remove it). If that measures OK then there is most likely some time delay circuit that has a bad capacitor.

If you measure any more than 100mV DC on any output and there are onboard trimpots to tame it, then the solution is simple. On something that old though, you may want to replace the trimpots.
 
marantz 1180dc feedback

Hi there Bruce and other hi fi gurus,

I have an issue with a marantz 1180dc also at present, the relay no longer kicks in and no sound comes through the speakers...any idea what the issue could be? the main fuse is ok and it still powers up, the sound just went dead as a song faded out one day...in terms of feedback on the amp...i find it to be very punchy - delivers a warm sound which detailed bottom end frequencies - that was typical of marantz from that era! Is it true that marantz never made their own output transistors but sourced them from toshiba? i noticed in my 1180dc, half of the output transistors are labelled toshiba and the other half branded marantz? Appreciate anyones help out there! Andy
 
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