Resistor keeps burning in my Marantz 1060! - diyAudio
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Old 2nd December 2004, 06:01 PM   #1
Giaime is offline Giaime  Italy
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Default Resistor keeps burning in my Marantz 1060!

Hello! I've got a problem with my Marantz 1060. A friend of mine gave it to me, and it was shot.
No sound from the left channel. I substituted the output transistors 'cause two of them were short, and it still didn't sound.
I subsituted a pair of burned resistors in the driver stage, and the driver transistors (perfect match subs!). After that, when I turned it on, it burned a pair of resistor either in the channel (the right one) that was good!
I substituted them with the exact values and much more power (basically the bigger that I could found that still fits on the board ).
I turned it on and it blowed a 220 ohm resistor, feeding the emitter of one of the driver transistors. The resistor is R738 and the transistor (good one, I checked) is H710. I think it should feed the +30v to the transistor. I substituted it and it still blows, with bad smoke.
On the other channel, there is the exactly same circuit, and the exact position resistor R737 doesn't blow.

I tryed to move a little trimmer on the board, R730, which I don't know what does (maybe the bias), I turned full clockwise, and I noticed that the resistor still burns, but somewhat slower. It smokes but starting later.

Help me! Don't know what to do!!!!!!!!!!
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Old 2nd December 2004, 07:22 PM   #2
Giaime is offline Giaime  Italy
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I already asked about the Marantz. Some good boy in this forum(don't remeber the name) gave me help. Please help me! I still can't find why my amp blows the resistor.
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Old 2nd December 2004, 07:29 PM   #3
tiroth is offline tiroth  United States
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I think you have already realized that the problem has nothing to do with the resistor. There is a problem somewhere else that is causing excessive current to flow through the output stage. Now, I am not at all an expert. But, with BJT amps that I have built in the past, depending on the error, the fault may blow anything (and everything) from the bias servo (if it exists) through the drivers to the output stage if the rails get pulled all over the place. So you may have already broken your replacements in an earlier step and yet not have corrected the first problem. Now, you must fix BOTH problems again if you've hosed the other stages.

Current limiting resistors might valuable in future attempts.
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Old 2nd December 2004, 08:37 PM   #4
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Default To avoid those blow resistors and transistors, put resistance in series with...

The positive rail and the negative rail too....100 ohms resistor 10 watts minimum.

If big current tried to enter the up amplifier part (from output line to plus line) the 100 ohms resistor will develop a lot of volts over it.... the amplifier voltage will reduce, this will help you to check without smoke components.

As your amplifier have no negative voltages related to ground...you will use only one resistor at positive line.

Despite of your supply are not simetrical related the zero volt point, the ground, the up part of the amplifier will show more positive voltage than the lower part. This way, if you fix one multimeter lead at the output line, the amplifier horizontal centered line, the one have one condenser with the plus side connected to it, ... the other meter lead will measure positive volts when touching the positive line..... beeing that voltage the half of the supply positive voltage.... your amplifier divides the sixty volts splitted in two parts..... so, you have zero volts at ground... 30 volts positive at the output line, the middle line...and 60 positive volts at the positive rail.....if you fix one meter lead in the middle, you will have 30 volts positive related and referenced this middle point, and the other side (ground side) will measure -30 volts...this side is negative related the mid line.

Your first transistors makes that voltage division... helped by some series resistor that travel from plus to minus, and have connections with the center line (the output line) to guarantee the voltage division in two halves.....If i can remember your amp uses only 60 volts plus and ground.

Your amplifier is unballanced.....more voltage and current one side related the other...this is not the bias....difficult to create so big problems...only is shorted or really big damaged.... the situation is that the side were the resistor NOT BURN, may be saturated, in other words, to much voltage at the transistor bases, and this is caused by the ballance voltage control that is made in earlier stages...check the earlier transistors one by one...check open resistors too.

If lower amplifier part is saturated, all 60 volts ( a little less) will circulate in the upper part... this will produce too much current passing inside the 220 or 270 emitter resistors.... this great voltage will produce enormous voltage over that resistor... see that this voltage will go to the output transistor base...it will conduct too much too...the lower transistor saturated represents a very low resistance in the earth direction..... the up transistor will burn colector to emitter, and sometimes base to emitter and colector...this way... 60 volts will pass inside the 220 resistor and it will burn too.

First do the stupid work, but it is the best in your case... do not spent too much time, as i done thinking what happened....remove one by one and test it..... have sure if you know how to measure transistors.... from base to emitter, and base to colector......now invert the multimeter leads collors, and check again..... if first measurement showed you conduct and conduct..... the inverted measurement must show you not conduct and not conduct...the multimeter position must be the diode position if digital unit..... at last check conduction from colector to emitter and invert..... cannot conduct and cannot conduct.... everything strange related that represents a damaged transistor.... check diodes too.... in one position will conduct, now invert....will not conduct anymore.... and measure your resistors, in special those that goes from Positive to ground, having connection in the output line...the center horizontal schematic line...the one is connected to the electrolitic condenser positive pin.

You may find some transistor bad.... some resistor burned or some condenser conducting.

I wish you good luck...latter i will search the schematic to help a little bit more.

The time i spend understanding the possibilities, are not too much inteligent... as removing transistors and measuring you will conclude things faster than the many logical possibilities of failures....one thing is guaranteed.... someone is damaged!....no joking talking obvious, because sometimes we think in misadjustments....see if some wire is cutted.... check solder, sometime you will repair just re-soldering parts... and remember that measuring transistor base to emitter voltages (carefull) you will see if voltage is going there correctly or if the component is damaged.... zero volts from base to emitter means base to emitter is shorted or voltage is not going there..... normal is to measure 500 to 650 milivolts DC over base to emitter.

Your amplifier center line, the output line must measure half the positive voltage.... exactly..... plus 30 volts in your case if i can remember....maybe some mistake....i have to check schematic...latter...now i cannot.

regards,

Carlos
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Old 2nd December 2004, 08:47 PM   #5
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Default R723 and R729, those trimpots will control the output line...

Will control the output line voltage (30 Volts) and will control the bias...... if well adjusted, over the 0.24 ohms resistors you must find from 15 to 25 milivolts...measuring DC directly over those resistor leads.... from ground to center line 30 volts.

Check those trimpots, check if someone is oppen as result of crack or over current burning the resistive rails...they used to work around the middle position, normally factory do not calculate those things to be adjusted in the maximum or minimum.

The guilty can be one of the transistors that are associated with those trimpots, as they adjust very important currents.

Now is hard work.

Carlos
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Old 3rd December 2004, 03:43 AM   #6
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Check coupling capacitors, I/P as well as O/P

Gajanan Phadte
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Old 3rd December 2004, 04:17 AM   #7
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Default This schematic may be easier to read

Take a look.

Carlos
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File Type: jpg mar. 1060.jpg (88.7 KB, 952 views)
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Old 3rd December 2004, 04:20 AM   #8
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Default This one a little bit more confused, as too many informs writted on it.

Those options have some voltages that can be very helpfull.

Carlos
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Old 3rd December 2004, 04:32 AM   #9
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Default UOOPS!!! I made supply invertion, both schematics already published are wrong!

I changed positive to negative, because used the lower half schematic....that one, beeing simetrical related the other channel, have the ground up.

In real life, without protection resistor or very fast fuses, your amplifier will burn a lot of parts.

But this happens when we assemble... already done amplifiers is a little bit difficult to make that.

This circuit is corrected related the invertion...use this one as a reference to your work.

arrivederci fratello, by brother

Carlos
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Old 3rd December 2004, 05:35 AM   #10
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Default Just to remember, may help some young guys too.

Here is the transistor check using analogue multimeters.

Carlos
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