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Old 22nd September 2007, 12:16 PM   #1
pezza89 is offline pezza89  Australia
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Default marantz 1180dc issue

Hey All,

Ive owned a lovely marantz 1180dc amplifier for nearly a year now, last week as a song was fading out, the music died...it still powers up, the main fuse is good, but no sound, the relay no longer kicks in...any thoughts on what could have happened?

I asked a friend about vintage marantz - he mentioned that marantz never made their own output transistors? is this true? i opened mine up- and half the ouputs are branded marantz, the other half are branded toshiba? hope someone out there might be able to help to cure this lovely amp! Cheers, Andy
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Old 22nd September 2007, 06:33 PM   #2
Bigred is offline Bigred  Canada
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The old thread you posted in with similar problem has some good info. I didn't see a problem tacking on to that thread but your here now so go through that thread again and check the DC offset for starters.
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Old 22nd September 2007, 07:40 PM   #3
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Track down a manual, for starters. Bigred has the right idea...if the output relay is not engaging, you need to find out why. Is offset so high that the protection circuitry is doing its job? Or is the protection circuitry at fault...in other words, the amp is fine but the relay will not engage because of a weak relay driver transistor or old dried-out electrolytic caps in the protection circuit?

Your job is to find out which is true...
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Old 22nd September 2007, 11:02 PM   #4
pezza89 is offline pezza89  Australia
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Question marantz 1180dc issue

Hey All,

Thanks for your replies! Being a novice and repariing hi fi - now i just gotta learn how to do all that!! What is the best way to test the elec capicators or relay transistor? I bought a manual of ebay from the states - its on its way as a first step! Cheers! Andy
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Old 23rd September 2007, 12:48 AM   #5
Bigred is offline Bigred  Canada
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Hey Andy,
If ya have the manual on its way and being a novice I'd just be patient and hang tight until it arrives. It will show the test point locations, DC offset adjustments and procedure etc. As far as testing caps, there are some basic quick checks you can do with a DMM but won't tell you the full story of a cap. I doubt you have the means to test capacitance, ESR, leakage etc. IMHO the BEST way is to just replace a suspect cap. Unless its had the electrolytics done before it probalby could use a FULL recap anyways. Before getting into all that lets get the manual and start with the relay problem. As EW stated, we need to find if its going into protection, a problem related to the actual protection/relay circuit or quite possibly the relay itself being bad. Give us a heads up when you get the SM and scanning it if possible will help us help you.
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Old 23rd September 2007, 01:58 AM   #6
pezza89 is offline pezza89  Australia
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Default 1180dc issue

Hi All,

Thanks for the advice thus far! its certainly put me in a better direction! I'll keep you all posted on how it goes! I bought the amp from the original owner, i dont think its ever been serviced, so it could probably do with some new caps etc. When i bought it, i stripped it down and cleaned all the pots and dust on the boards as a starting point...im excited to learn the next steps in changing caps etc. I'll post some photos over the next few days! Cheers, Andy
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Old 4th December 2007, 07:14 AM   #7
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Hey all,
I have taken over this repair for Andy, and the good news is that it is up and running again and sounds lovely. The fault was a shorted diode block in auxiliary power supply.
I have given it a good check over, fixed up suspect joints and replaced a few suspect looking caps on the power amp board.
However I am wondering about the bias current. Surprisingly there is no adjustment for it, and the amp is running a bit too warm for my liking. If you leave it on and idling (no signal) for a few hours the heatsink is uncomfortable to touch for more than a five seconds or so - and in my books that's too hot.
I have checked and set DC offset - that's a funny thing too. I set it as per the way I would on any amp (DMM on speaker output terminals, zero signal, set for 0v) and it's all good. The manual, which I have since obtained from Andy, instructs to measure between pins JN01 and JN05 (or gnd) (L channel). R channel is JN04 and JN06 (or gnd). These are clearly the wrong pins based on both the amp itself and the circuit in the very same manual! They are not even symmetrically related to each channel! There a quite a few inconsistencies between joining plug numbers on schematics and on board layout diagrams in the very same manual too! *sigh*
But that aside, there is no info at all on bias adjustment or checking in the manual.
So my question is - does anyone have experience with how to change the setting? Or any other info that may help? At the moment the current is running at about 75 - 80Ma which isn't ridiculous but does seem on the high side, and I expect it would cool down a bit if I could bring it back to about 40.
Any thoughts appreciated
Sam.
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