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MARANTZ 30 problem
MARANTZ 30 problem
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Old 23rd January 2010, 08:06 PM   #1
oldmarantz is offline oldmarantz
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Default MARANTZ 30 problem

Hello all...
I need some advices
I picked up this rare and early Marantz 30, but this amp. has a small default
when I switch on the tone command, the relay switch off and come back on and I loose one channel, when the tone is off the amp. works well...I have no schematics I think the problem in on the pré board what do you think about that...
If someone has the marantz 30 service manual it will be great... Thanks for your help!
Dominic
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Old 23rd January 2010, 09:48 PM   #2
llwhtt is offline llwhtt  United States
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All of those blue axial electrolytics need to be replaced for a start. Many 70s amplifiers used those caps and trust me they need to go. May or may not be causing this particular problem. I recently repaired an old Acoustic guitar amplifier, replaced close to fifty of those caps and it worked fine after that.

Craig
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Old 24th January 2010, 08:14 AM   #3
oldmarantz is offline oldmarantz
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Ok I kill them already!
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Old 24th January 2010, 08:21 AM   #4
Mooly is offline Mooly  United Kingdom
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MARANTZ 30 problem
Is the tone control "defeat" (think that's what you mean) done via switches or does it use a relay for signal switching ?
Relays can go faulty... dirty contacts.
Which relay do you mean clicks off ?
Do you mean the protection relay and the speakers are being disconnected ?

Need a bit more info
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Old 24th January 2010, 08:26 AM   #5
oldmarantz is offline oldmarantz
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Yes it is the main protection relay, there is no other relay in this amp.
when you switch on the tone rotactor it goes off for a 1 or 2 seconds and on again and one channel becomes very weak the other is good...

when you don't use the tone the amp works well...
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Old 24th January 2010, 08:52 AM   #6
Ruwe is offline Ruwe  Europe
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Hi,
I would check first the selector switch itself. Are you sure it's making a good contact when you switch it to tone control, and that it is disconnecting properly from the "direct" position? ... That's easy to check first.

In my opinion you may have an open when you turn the switch to tone control. May be this switch is in the feedback path of some IC ot transistor (I'm not familiar with this amp) and this creates a DC voltage at the output, which turns on the protection....

If the switch is fine, then you should find the tone control circuit and check the components. You might have a faulty transistor/IC, shorted diode or capacitor, causing bias problems ... It could be practically anything, causing a short DC discharge, enough to activate the protection for awhile.
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Old 24th January 2010, 11:39 AM   #7
Mooly is offline Mooly  United Kingdom
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MARANTZ 30 problem
OK... main protection relay tripping out.
From what you now say I would agree with Ruwe's suggestions.

You really need to see a circuit. Putting tone controls in the feedback loop of a poweramp is an old technique dating back to valve gear.
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Old 24th January 2010, 11:49 AM   #8
oldmarantz is offline oldmarantz
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It works.... I changed blue caps on the pré board but it wasn't the problem ,one tr (pnp: mpsa70) at the output of the pré. was dead, I had 7vdc on the output of the préamplifier... good job!
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Old 24th January 2010, 12:01 PM   #9
Mooly is offline Mooly  United Kingdom
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MARANTZ 30 problem
Excellent news...
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Old 24th January 2010, 01:17 PM   #10
oldmarantz is offline oldmarantz
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Yes and believe me this amp. rocks
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