Resistor keeps burning in my Marantz 1060!

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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. :confused:
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! :eek:
I substituted them with the exact values and much more power (basically the bigger that I could found that still fits on the board :D ).
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. :hot:
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. :confused:

Help me! Don't know what to do!!!!!!!!!! :bawling:
 
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.
 
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
 
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
 
This schematic may be easier to read

Take a look.

Carlos
 

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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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Dear DestroyerX, I've checked your schematic (thanks!!!!!!) and I've found that you think the n. one suspect is the H704. Well, I didn't checked it when I made the repairs! That's because it is the only big metal transistor on that board that doesn't have a dissipator, so i thought it should be an audio preamplifier, or something that not deals with high voltages and power. I will check them today. Maybe it needs a dissipator? Maybe it had one but now it is lost? Could be strange because the dissipators on the other driver transistors are not joined with silicon grease, but with glue!

I will check... If I have to substitute it, what sub do you suggest? I mean, should I go with the 2n1974 that the guy in the store told me or I should buy a more rugged one?
 
Hjelm, when i can do something, in special for the ones i see that need help...

I feel good!.... alike when you give some gift to someone...you feel good seeing the one that received the gift happy.... we share the "good feelings" this way.

I am not religious, i can believe in my own ignorance...and i have a name i give to that....but if i start to think in God....it is clear that he can be translated as feelings.

hehe, already paid doing.... and i guarantee to you that i fell more happy than Giaime.
----------------- ------------------- ---------------------
Giaime, dear fratello, ma nonna di firenze...Danesi famiglia...

Giaime, my dear friend, my grandmother came from florence - Italy, the family name is Danesi, that means, the Danish one... and this is incredible to me...as i am opposite as Danish people...my grandmother really had some similarities...she smiled only in Christmas or to make a photography.... i smile alike a fool all the time, may be a fool!...no problem...but happy man!...real happy!.... danish people, some of them smile a lot...not so often, as temperature may break some piece of the lips....low temperature problems.

Giaime, in my mind, transistor is transistor and not more than transistor, it have tree leads, one is base, second colector and third is emitter.

They have some characteristics to take into account.

The voltage they can support referenced the circuit it will work... so, some amplifier with 50 watts RMS can have more than 55 volts peak to peak.... this way, the transistor to that case must support Volts from colector to emitter voltage bigger than that... twice or more than that.

One amplifier that can produce 50 watts RMS, may produce 100 watts at 4 ohms (if supply can maintain voltage...not normall, ... normally the supply loose 30 percent when hard loaded)... and can also produce 200 watts for small period of times...when you switch on and filter condensers charged....the fuse will burn...but, your transistor must hold that 200 watts power.... and they call that "dissipation power max".... the maximum capacity to transfer heat to the heat sink without melt the small chip inside (the real transistor)... when capsule is measuring 55 degrees...inside the temperature is near to melt things!

Another important characteristic is that transistor have their own current limit.....to have those 200 watts over 2 ohms resistor, a small time rush current may be 10 amperes... so.... if you transistor are smaller than that...hehe....may booooommmm!

Other important characteristic is the -3dB frequency roll of...in other words, the frequency where the transistor loose 3db in their output voltage.... with constant alternate voltage , and frequency going in...capsule maintained at 25 degrées centigrades using enormous refrigerator machines... that frequency, people say that will produce better hi frequency...lets see...20 Khz (no one can hear) when it has the capacity to work around 150 Megahertz..... this way, people say that harmonics are present.... 40 Khz, 80 Khz... that those sounds cannot be perceived by your conscience...but that make some vibration inside your ears, sending some informs to your brain... and that inform is resulted in a "feeling of reality".... in real world... 10 Megahertz transistors may work very well..... the bigger frequency ones have empathy to oscilate like a hell... and can create more problems than solutions....making wave over sinusoidal waves.... crispy sound.... some people love crispy sound!

Other characteristic is that the bigger they are in current, the smaller they are in gain....

They do not like heat... and need a 10 square inches of aluminium to each 10 watts consumption (not output power )...see the amplifier back!

More than that Giaime, Marketing, Preferences, Appearance... my friend are using.... Mr Good are using, the designer Mr. Project told are interesting.... the price, the size...the color....and many can make the same job.

I do not believe that this transistor sounds this or that way...could not perceive those .... only small differences in hi frequencies because of the top frequency capacity.

So, to be safe.... use the biggest, more modern output Motorolla units to output.....the biggest Sanken.

To the drivers...use the ones good designs are using... ask Hugh Dean from AKSA by example...or see the forum designs of amplifiers.

To the voltage amplifiers, those one are important...the one you have not a good heatsink may be the one...not sure....this one produces all the voltage you will find in the output... the responsability is incredible.... i like to use 2SC2338, but hugh has better, and more modern ideas.

To first stage, those differential must be matched in gain, and low noise...there are 1237464637828487547548498499544743438584584959499495949545 of units you can use.... check the ones people are using.

If i am in doubt i use TIP35 or 36, depends the polarity to output, or the bigger motorola ones ....have no one in hands now...MJ15024...i do not remember....to drivers i like to use, when in doubt 2SA948 and 2SC2338, to Voltage amplifier i use 2SC2338 and to input BC556/546.

Transistor have some charge line, in other words, the voltage point were it works good, this way, as i have not those graphics in my hand.... i go to good amplifiers schematics and the informations i capture from those guys.

The best you can make is to keep the ones factory used, as others cannot be exactly the same...if not possible.... as your amplifier use 60 volts.... find schematics with that voltage, or the ones with plus 30 and minus 30 to make your transistor choice.

I think that choice is really personal...here...TIP41/42, maybe 30 watts constant transistor (specification is bigger..hehe...never trust entirelly).... 4 amperes to 6 maximum constant.... 1 to 5 Megahertz maximum.... gain low...from 40 to 80 normally...but it cost 6 units for a dollar!....BD139 are wonderfull as drivers to voltages up to 40 volts.... can use it as RF transistor too, it can oscilate (work) at 30 megahertz, producing some watts... also to low voltage, to the input i use BC547/557, to higher voltages...higher than plus and minus 35 volts, i jumped to BC546/556. To voltage amplifier i use BD139/140, depending the polarity.... and to high voltages i jumped to 2SC2338... may be 150 Volts, 1,5A, 20 Watts and more than 100 Megahertz...something alike that...not a precise specification.

Each one have their preferences... some guys say that transistor "sounds"... other say that transistor do not make special sound...others that transistor are critical...i defend the flag that they are not critical... and many discussions can derive from that.

Having that "Kit" i told, you will have conditions to assemble several amplifiers, and to fix several amplifiers too.

My old Army Sargeant Ottmar Albert Furrer, son of a Swiss man, always said to me.. do not loose time thinking, as this can delay too much, and time is money...under combat you cannot think anything bigger than try to survive...so...replace parts...if have them, do not even need to check if damage or not...do it after the radio is working.

Now i am thinking, doing as exercise....but remove and test is faster... and the answer will came...if you do not need to prove nothing to yourself.... just remove, test them and substitute them.

regards,

Carlos
 
Dear DestroyerX, I thank you for your help. But didn't you find your reply a little off-topic? Or maybe too long, or too obvious for someone that has already that knowledge?

And you already sad to me that your grandmother came from Florence... Do you know that I've never been in Florence?

Apart from that, let's return to the topic. Again, thanks to all!!!

(stand waiting for news about that amp...)
 
I've looked at the amp, and it turned to be H704 that was open from B to E (checked either polarity with a DMM set on "diode test"). I will go to the shop in the next week, I've got too much to study at school this period!

Do you think I should sub both the two transistors on the two channels? I plan substituting it, as you can't predict what you will get from a 30 years old and probably overheated transistor.
And should I put a dissipator on it? It is a 2sc875d...
 
I am terrible sorry, if you took my detailed explications as an ofense to you...

I cannot evaluate people knowledge reading the empty profile.

My Magic today is week, and could not see you between the smoke.

Also, telephatic transmission is suffering from radio frequency interference... so could no enter your brain.

When you do not know, how many, the age, the experience of the topic readers, better to reduce to a more simple form, to reach more people.... this way, the big Doctors and the more simple student will understand.

I think you are rigth when i make so big efforces and was misunderstood.....but this happened with you...others can feel good to that basic, beginner informations.

Also i cannot imagine that all Italians are happy to meet other Italian family outside Italy soil

I am sorry very much to make you fell bad.... but i think we can go on, as we do the best we can, related one each other, i gave you my best... and you may gave me your best.

Related to fell bad, you may feel bad.... but i also...so.... we are in the same boat man...have a beer and let's go on, as life will give to us better moments.

regards,

Carlos
 
Quote:
"Do you think I should sub both the two transistors on the two channels? I plan substituting it"

Certainly wont hurt, however if your going to do any
preventive maintenance I would also focus on the passives
mainly the electrolytic caps when they get this old they can
cause lots of problems.
 
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