Dear DestroyerX,
I haven't feel bad about your answer. Nor I am a big experienced one; I just pointed that you were going little off-topic. And you know, for the good of this great site, we must keep the posts in-topic.
I am very thankeful to you! You helped me much, without you I think I'll have it serviced from a tech (who probably would told me to throw away it). Maybe I have been a little too aggressive in your anwer... excuse me.
Yes, i will sub the transistors in both channels, also I plan to get rid of the old electrolitics: I think the six big ones on the power amp board, the 47uF 50V....
Do I need a dissipator on the new transistors?
I haven't feel bad about your answer. Nor I am a big experienced one; I just pointed that you were going little off-topic. And you know, for the good of this great site, we must keep the posts in-topic.
I am very thankeful to you! You helped me much, without you I think I'll have it serviced from a tech (who probably would told me to throw away it). Maybe I have been a little too aggressive in your anwer... excuse me.
Yes, i will sub the transistors in both channels, also I plan to get rid of the old electrolitics: I think the six big ones on the power amp board, the 47uF 50V....
Do I need a dissipator on the new transistors?
Help! I replaced the transistors that DestroyerX said, and all the electrolytics in the power amp board, and the same resistor keeps burning!
This resistor is not new, had already smoked, but not burned. Smoking resistors are plain bad or not? I measured it and I still get it's nominal value... Maybe the power dissipation rating is not the same as a new one? Do I have to change it? It's looking like I got to go ANOTHER TIME to the repair shop... up to now I went there about 11 times, both for my Sansui and this *******' Marantz...
So what do you think about burned resistors?
This resistor is not new, had already smoked, but not burned. Smoking resistors are plain bad or not? I measured it and I still get it's nominal value... Maybe the power dissipation rating is not the same as a new one? Do I have to change it? It's looking like I got to go ANOTHER TIME to the repair shop... up to now I went there about 11 times, both for my Sansui and this *******' Marantz...
So what do you think about burned resistors?
I forgot to mention that the other resistor in the other channel burns too... And that hasn't been overheated! Help Me!
Maybe 1 watt is too small? These are big! and the original ones were smaller... Maybe I need a beefier one to support the new currents (remember that I've substituted the output transistors and the driver ones - but the subs are right for the originals... taken from the books!)
Maybe 1 watt is too small? These are big! and the original ones were smaller... Maybe I need a beefier one to support the new currents (remember that I've substituted the output transistors and the driver ones - but the subs are right for the originals... taken from the books!)
Quote: "I forgot to mention that the other resistor in the other channel burns too... And that hasn't been overheated! Help Me!
Maybe 1 watt is too small? These are big! and the original ones were smaller... Maybe I need a beefier one to support the new currents (remember that I've substituted the output transistors and the driver ones - but the subs are right for the originals... taken from the books!)"
Ok lets back up a bit.
First off if you have resistors smoking its because of another
component somewhere else in circuit and not because you
need bigger resistors. You say youve subbed the transistors
What exactly did you sub them with?
Maybe 1 watt is too small? These are big! and the original ones were smaller... Maybe I need a beefier one to support the new currents (remember that I've substituted the output transistors and the driver ones - but the subs are right for the originals... taken from the books!)"
Ok lets back up a bit.
First off if you have resistors smoking its because of another
component somewhere else in circuit and not because you
need bigger resistors. You say youve subbed the transistors
What exactly did you sub them with?
About the resistance between the transistors and the heatsinks (I think you mean the output ones, not the drivers): the transistors are insulated from the heatsink by a plastic sheet, and the connections on the trs are full (i.e. there are 3 wires, not just two and the ground given by the chassis like in low-cost equipment). And those wire are properly soldered and insulated.
Quote: "First off if you have resistors smoking its because of another
component somewhere else in circuit and not because you
need bigger resistors."
I already replaced every transistor on that board that deals with the output (I mean I didn't substituted the ones that deal with small-signal audio only) as DestroyerX from Brazil suggested.
I understand that I don't need more power in the resistor, but should I need a bigger value? Maybe 300/390ohm? I think this because I substituted the transistor, and maybe the new ones draw too much current... I don't know...
Quote: "You say youve subbed the transistors
What exactly did you sub them with?"
I subbed the NPN output ones (they are all NPN 'cause it's a class A single ended parallel output stage) named 2SC897 with MJ15003, and for the drivers that were all 2SC875D with 2N1974 as the guy in the electronic shop told me. He read this from the books! And no, I haven't burned anything while soldering... It's hard to kill a silicon transistor with a 15W iron...
It seems to me that the problem is due to maybe two things:
- there is another broken thing in the power amp board that I can't find. It can't be a transistor because I substituted all the important ones. Also many electrolitics have been replaced, with the 0,24 ohm resistors in the final stage (one showed to me 50k, strange).
- the new output transistors, the driver ones or both sucks too much current. In this case I think I have to tweak some resistor values. I noticed that if I move the bias trimpots around, the smoking didn't stop, so this is not a minimal problem.
Anyone has ideas? Someone that knows well the Marantz output stage that shows me some tricks to fix it?
Quote: "First off if you have resistors smoking its because of another
component somewhere else in circuit and not because you
need bigger resistors."
I already replaced every transistor on that board that deals with the output (I mean I didn't substituted the ones that deal with small-signal audio only) as DestroyerX from Brazil suggested.
I understand that I don't need more power in the resistor, but should I need a bigger value? Maybe 300/390ohm? I think this because I substituted the transistor, and maybe the new ones draw too much current... I don't know...
Quote: "You say youve subbed the transistors
What exactly did you sub them with?"
I subbed the NPN output ones (they are all NPN 'cause it's a class A single ended parallel output stage) named 2SC897 with MJ15003, and for the drivers that were all 2SC875D with 2N1974 as the guy in the electronic shop told me. He read this from the books! And no, I haven't burned anything while soldering... It's hard to kill a silicon transistor with a 15W iron...
It seems to me that the problem is due to maybe two things:
- there is another broken thing in the power amp board that I can't find. It can't be a transistor because I substituted all the important ones. Also many electrolitics have been replaced, with the 0,24 ohm resistors in the final stage (one showed to me 50k, strange).
- the new output transistors, the driver ones or both sucks too much current. In this case I think I have to tweak some resistor values. I noticed that if I move the bias trimpots around, the smoking didn't stop, so this is not a minimal problem.
Anyone has ideas? Someone that knows well the Marantz output stage that shows me some tricks to fix it?
Ok I know you must be getting frustrated about now.
But lets hit the brakes take a breath and lets take a
different approach to this. First off the MJ15003 should
require no modification of the unit to get them to work right.
This whole thing is being caused by a missed passive someplace.
Which by the way is all it would take.
Now before you run off and start buying parts lets make a
thorough assessment of what your going to need first.
Lets take this one step at a time. First remove all transistors
from H703 and 704 all the way through the outputs and just
set them aside for now. Next go through and check ALL resistors
for value. If you run into one that’s out of range then desolder
at least one leg and check again. Any ones you find that
are out of range, open , shorted, whatever take note where
they go and set them aside. Next focus on the electrolytic
caps. First check the ones you replaced and make sure their
ok. You want to make sure none you replaced are open or
shorted. Next make a list of all the electrolytic caps in the
power amp section that you didn’t change and make a list
of them and just figure on replacing them “ Their nearly
30 years old their due”. Next take your ohmmeter and
check all the variable resistors on the board. R723 and 724
which are 100k and R729 and 730 which are 470ohm.
Your looking for opens or shorts here.
Ok I’m going to stop here for the time being. Do this first
and report back. Don’t worry I will get to the semiconductors
later.
Glen
But lets hit the brakes take a breath and lets take a
different approach to this. First off the MJ15003 should
require no modification of the unit to get them to work right.
This whole thing is being caused by a missed passive someplace.
Which by the way is all it would take.
Now before you run off and start buying parts lets make a
thorough assessment of what your going to need first.
Lets take this one step at a time. First remove all transistors
from H703 and 704 all the way through the outputs and just
set them aside for now. Next go through and check ALL resistors
for value. If you run into one that’s out of range then desolder
at least one leg and check again. Any ones you find that
are out of range, open , shorted, whatever take note where
they go and set them aside. Next focus on the electrolytic
caps. First check the ones you replaced and make sure their
ok. You want to make sure none you replaced are open or
shorted. Next make a list of all the electrolytic caps in the
power amp section that you didn’t change and make a list
of them and just figure on replacing them “ Their nearly
30 years old their due”. Next take your ohmmeter and
check all the variable resistors on the board. R723 and 724
which are 100k and R729 and 730 which are 470ohm.
Your looking for opens or shorts here.
Ok I’m going to stop here for the time being. Do this first
and report back. Don’t worry I will get to the semiconductors
later.
Glen
Hi Giaime,
Your 2N1974 is only good to 60V C-E, the original was 75V. Also, the DC gain is a bit low. You could change the case style and use something like 2SC3421 and 2SA1358. You have an NPN and PNP driver (2SA606). Your outputs are overkill for ratings, possibly the gain is a little low. They will work.
These units are very reliable, so your repair should last a long time - as long as you keep your end up. The design is conservative, nothing overheats in normal operation.
One comment. More parts are overheated with low wattage irons than 40W irons. Temperature controlled stations sell for less than $100.00 CDN. If you do much of anything, buy one.
-Chris
Your 2N1974 is only good to 60V C-E, the original was 75V. Also, the DC gain is a bit low. You could change the case style and use something like 2SC3421 and 2SA1358. You have an NPN and PNP driver (2SA606). Your outputs are overkill for ratings, possibly the gain is a little low. They will work.
These units are very reliable, so your repair should last a long time - as long as you keep your end up. The design is conservative, nothing overheats in normal operation.
One comment. More parts are overheated with low wattage irons than 40W irons. Temperature controlled stations sell for less than $100.00 CDN. If you do much of anything, buy one.
-Chris
Thank you guys! I will check everything on that board and I will report later! Today I have a free morning, the schools are closed....
Wait a moment: about the voltage rating of the 2N1974: The guy in the shop said that the 2SC875D was rated at 120V, and my subs are rated at 100V. I said "I don't care, the rail is at 60V...." Are you sure of your ratings? If you're right maybe I found the SOLUTION....
What a big deal to desolder everything! The Maranzt is definitely not a "repairman-friendly amp"! The board is vertical in little space, connected by wires. What an hard work!
Thank you all guys, I will report later.
Wait a moment: about the voltage rating of the 2N1974: The guy in the shop said that the 2SC875D was rated at 120V, and my subs are rated at 100V. I said "I don't care, the rail is at 60V...." Are you sure of your ratings? If you're right maybe I found the SOLUTION....
What a big deal to desolder everything! The Maranzt is definitely not a "repairman-friendly amp"! The board is vertical in little space, connected by wires. What an hard work!
Thank you all guys, I will report later.
You know what else? You're right. The 2N1974 are rated for Vcb 100V, Vce 60V. For the original ones, 2SC875, I haven't been able to find info, but a strange japanese electronic-supply site said "NPN, Uni, Si, 75V, 0.2A, 0.5W". I suspect that this "75V" is Vce, and so the guy in the shop has given me some transistors rated only for 60V. The rails in this amp is just 60V, maybe little more, and it frigged the transistors. I will have to check, but I think I'm right.
So guys, what transistor should I replace with?
So guys, what transistor should I replace with?
Yeah, right! I was just saying that the maximum voltage found in the amp is 60V... just a safety margin for capacitors, diodes... AND TRANSISTORS.
I've looked at the amp after lunch and I've got all the drivers (2N1974, on the board H709/710/711/712) open or shorted...
And also H708, wich I haven't substituted, still original, I haven't looked at it until today...
I also got the two 220ohm (R737-R738) burned and I will replace them, with another 220ohm one that says 189ohm on the DMM (it was R739 or R740 I don't remember). Also the germanium diodes will be replaced, just for safety (these old germanium 1N60 I think are not so reliable in a power amp...) I also got R743 that the schematic says 10ohm, but in the amp I found a brown-orange-black, a 13ohm. Strange! I will replace it.
The electrolitics are all good, and also the trimpots (a little drifted - 105k and 82k for the 100k ones, 407 and 513 for the 470 ones, not gonna replace them).
What should I buy to replace the blown 2N1974 (original 2SC875)? I searched my books and I found these high voltage (just to be sure) transistors: MPSA42, 2N3019, ZTX453, 2N3440.
What do you think about them?
But if they must have 30V on them, why the 2N1974 were broken? Maybe it's not a voltage issue like I thought... But I've checked pretty everything (but I will continue checking) on that board, and remeber that before I put my hands onto it, the right channel worked with no burns or smokes or whatsoever! So it must be a poweramp-board fault. I checked also the output transistors and they are good (hard to kill those MJ15003!). Also checked for PCB shorts, blobs of solder, cold joints... Nothing.
I still can't figure why the 2N1974 blew out...
I've looked at the amp after lunch and I've got all the drivers (2N1974, on the board H709/710/711/712) open or shorted...
And also H708, wich I haven't substituted, still original, I haven't looked at it until today...
I also got the two 220ohm (R737-R738) burned and I will replace them, with another 220ohm one that says 189ohm on the DMM (it was R739 or R740 I don't remember). Also the germanium diodes will be replaced, just for safety (these old germanium 1N60 I think are not so reliable in a power amp...) I also got R743 that the schematic says 10ohm, but in the amp I found a brown-orange-black, a 13ohm. Strange! I will replace it.
The electrolitics are all good, and also the trimpots (a little drifted - 105k and 82k for the 100k ones, 407 and 513 for the 470 ones, not gonna replace them).
What should I buy to replace the blown 2N1974 (original 2SC875)? I searched my books and I found these high voltage (just to be sure) transistors: MPSA42, 2N3019, ZTX453, 2N3440.
What do you think about them?
But if they must have 30V on them, why the 2N1974 were broken? Maybe it's not a voltage issue like I thought... But I've checked pretty everything (but I will continue checking) on that board, and remeber that before I put my hands onto it, the right channel worked with no burns or smokes or whatsoever! So it must be a poweramp-board fault. I checked also the output transistors and they are good (hard to kill those MJ15003!). Also checked for PCB shorts, blobs of solder, cold joints... Nothing.
I still can't figure why the 2N1974 blew out...
And I forgot to mention: what should I replace for H708? I would replace all of them, to mantain balance between the channels, so I will replace H705/706/707/708.
Could that small forgotten transistor be the cause of the disaster?
I think they drive the drivers (a word joke), but it was open, not shorted...
Could that small forgotten transistor be the cause of the disaster?
I think they drive the drivers (a word joke), but it was open, not shorted...
Hi Giaime,
Read my previous post. H709 and 710 are NPN - 2SC3421. H711 and 712 are PNP - 2SA1358. The originals were 2SC959 and 2SA606, a different case style. I use these and they work in this amp. H705 and 707 are overcurrent protection transistors. H005 is the bias diode assy. (SV-3A is the original).
You can remove the protection transistors for now and test them later. Reinstall them when you have the amp working. Don't worry about the amp having different transistors per channel. Right now, one channel works. Don't mess with it. Later, if you really wish, you can replace those parts.
You could also use MJE243 (NPN) and MJE253 (PNP) to replace the driver transistors. Use On Semi parts if you have a choice. These are a similar case style to the others I suggested.
Your amp burned the transistors because you had NPN parts installed where PNP parts belonged. Finally, try not to use ECG's or NTE's. If you do, just pour gas into the unit and light it as you walk away.
-Chris
Read my previous post. H709 and 710 are NPN - 2SC3421. H711 and 712 are PNP - 2SA1358. The originals were 2SC959 and 2SA606, a different case style. I use these and they work in this amp. H705 and 707 are overcurrent protection transistors. H005 is the bias diode assy. (SV-3A is the original).
You can remove the protection transistors for now and test them later. Reinstall them when you have the amp working. Don't worry about the amp having different transistors per channel. Right now, one channel works. Don't mess with it. Later, if you really wish, you can replace those parts.
You could also use MJE243 (NPN) and MJE253 (PNP) to replace the driver transistors. Use On Semi parts if you have a choice. These are a similar case style to the others I suggested.
Your amp burned the transistors because you had NPN parts installed where PNP parts belonged. Finally, try not to use ECG's or NTE's. If you do, just pour gas into the unit and light it as you walk away.
-Chris
Sorry (for me) guys, but it seems that I have put NPN transistor for ALL the drivers (H710, H712, H711, H709)! 
Instead there are two pnp and two npn.
I will replace them and report!
Sorry for such a stupid error! But I remeber that these transistors had all the same number on them, maybe I missed a letter or something. Thank you all guys, and wait for a report about the substitution.
How stupid am I! I've thrown away 5 euros of transistors...
Instead there are two pnp and two npn.
I will replace them and report!
Sorry for such a stupid error! But I remeber that these transistors had all the same number on them, maybe I missed a letter or something. Thank you all guys, and wait for a report about the substitution.
How stupid am I! I've thrown away 5 euros of transistors...
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