Now i unerstand why you are talking about the VOM, maybe i find something used on ebay.
I live in Italy, so buying stuff from US is quite difficult.
I would like to ask:since the only problematic op amp is the #7, which controls the xlr output, can i assume that it shouldn't be the culprit of the problems of this speaker?
I mean.. It makes sense to me..
You said :
" SO you can solve some problems with the DVM on DC volts scale. pins 2 & 3 should be about the middle of the power supply rails, in DC. "
I can't understand this, i mean.. I've got about 0 V measuring every IN of every op amp.
Hai ragione amico argentino.. 🙂
0 v is the middle lf the supply rails. The supply rails are +15 and -15 aren't they?
Farnell operates in Italy, they probably have stock in country that they have already paid customs duty etc on. Just your VAT pertains. Type VOM in the search box, see what you get. TENMA is *****ese ****, I wouldn't waste $30 on one unless it has 5000 ohms/volt rated AC scales and a <40 VAC and <5 VAC scale.
Not when you could buy a 270 that might last the rest of your life, that has 20 vac and 2.5 vac scales. Below 5000 ohms/volt rating you might not be able to look at the input of the first op amp and see anything. Although a transistor radio pumps some current out the earphone jack, that is why I use them. My Peavey CS800s amp has a microphone input in addition to the high level one, if there was a problem there it would take a sensitive (5000 ohms/volt or higher) VOM to see the music. I had made a bad solder joint on my input cap fixing the PV-1.3k replacing the 18 year old electrolytic cap; I found it with the VOM. Music went inta, came out of cap lead, didn't make it inta the input resistor on the op amp. Bad solder joint.
Dear indianajo, sorry for not being clear (although in fact I was answering chiunana directly) , "Larsen effect" refers to acoustic feedback, which in Latin languages is a different word from electric feedback.
English has a limited vocabulary and often uses the same word for different objects or meanings, what causes lots of problem to automatic translators ... that's why I preferred to answer this particular doubt straight in Italian.
English has a limited vocabulary and often uses the same word for different objects or meanings, what causes lots of problem to automatic translators ... that's why I preferred to answer this particular doubt straight in Italian.
Entiendo un poco del Espanol, pero no hay dictionarios de papel con palabras tecnicas. Lo siento.
Oh dear, you're right.
I am searching on farnell and others.. Meanwhile i would like to continue troubleshooting, i will post here if i'll have questions.. And i surely will.
Thanks to all of you. 😱
Hey guys, i am back.
Now i've got to say: shame on me.
Apparently i got confused between the two amps.. I was measuring the rail voltages on the good one.
I don't tell you how i discovered 'cause you would laugh until christmas, it's not important anyway. 😀
Basically i do have problems on the rail voltage of all the pre. Nothing arrives, zero, from the power supply.
So i started to measure from the very beginning, that is the cables out from the transformer. I got +- 15 v as expected.
But from there... I got the rs205, two caps (altough on the scheme i have 4 caps, the scheme is wrong - c31 and c33 are missing) and the 7815 and 7915.
It's like if the voltage disappears, on the input of the 7815 i have 0.6 v and an output of 0, on the 7915 i've got as input and output 0.57v.
I am sure the 205 is ok, i tried to replace it and i got the same behaviour. Actually i thought that i should be able to measure the unfiltered V between the +- terminals. I have 18 V on the other amp, and it makes sense. On the bad one i have just some tiny 0.2 V or so.
I tooked it out from board, ihave the correct voltage drop on the pins. I tried to put the good one on the bad board and as i said i had the same result.
Same for the voltage regulators..
Could it be the caps? I measured the capacitance on the board, but it doesn't make sense, does it? I had a very little value of C.
Thinking about it, i couldn't explain it if they would be the culprit. I am worried to desolder them, don't wanna destroy the board. Externally the look brand new, no bulge on top...
What should i do, in your opinion?
Have a nice day...
Now i've got to say: shame on me.
Apparently i got confused between the two amps.. I was measuring the rail voltages on the good one.
I don't tell you how i discovered 'cause you would laugh until christmas, it's not important anyway. 😀
Basically i do have problems on the rail voltage of all the pre. Nothing arrives, zero, from the power supply.
So i started to measure from the very beginning, that is the cables out from the transformer. I got +- 15 v as expected.
But from there... I got the rs205, two caps (altough on the scheme i have 4 caps, the scheme is wrong - c31 and c33 are missing) and the 7815 and 7915.
It's like if the voltage disappears, on the input of the 7815 i have 0.6 v and an output of 0, on the 7915 i've got as input and output 0.57v.
I am sure the 205 is ok, i tried to replace it and i got the same behaviour. Actually i thought that i should be able to measure the unfiltered V between the +- terminals. I have 18 V on the other amp, and it makes sense. On the bad one i have just some tiny 0.2 V or so.
I tooked it out from board, ihave the correct voltage drop on the pins. I tried to put the good one on the bad board and as i said i had the same result.
Same for the voltage regulators..
Could it be the caps? I measured the capacitance on the board, but it doesn't make sense, does it? I had a very little value of C.
Thinking about it, i couldn't explain it if they would be the culprit. I am worried to desolder them, don't wanna destroy the board. Externally the look brand new, no bulge on top...
What should i do, in your opinion?
Have a nice day...
I've confessed the bad solder joint I made replacing e-caps based on the calender. You can certainly entertain us with your newbie foibles. Red tape or a sticker "mal" on the bad one might be useful.
I made another bad solder joint putting fuses in the O.T. base line to try to keep the shorting output transistors from blowing up 50 other parts. Made the output transistors oscillate; that was entertaining ! I found it without a scope, by listening to the speaker (weird sounding) and changing input caps on the VOM (390 pf, 20 VAC still there, must be ultrasonic oscillation).
You can both have shorted 15 v filter caps, or you can have a solder bridge between the traces, or you can have solder flux burned to carbon between the board traces.
You could also have a blown diode bridge, or a bad solder joint on it. This is part 431? The bridge you can measure out of circuit- one diode drop between either AC terminal and plus, between minus and both AC terminals. Check backwards too, you should get 9999 ohms backwards. The 15 v bridge is protected against an internally shorted diode with two 1k resistors series with the AC input. If one of these resistors is dropping the whole 16 VAC then either the bridge or something thereafter is shorted.
E-caps don't have to blow their tops to be defective. They are some of the most likely parts to fail after 5 to 15 years depending on the quality initially purchased. If your bridge has floppy wires on it, I'd unsolder that first.
I made another bad solder joint putting fuses in the O.T. base line to try to keep the shorting output transistors from blowing up 50 other parts. Made the output transistors oscillate; that was entertaining ! I found it without a scope, by listening to the speaker (weird sounding) and changing input caps on the VOM (390 pf, 20 VAC still there, must be ultrasonic oscillation).
You can both have shorted 15 v filter caps, or you can have a solder bridge between the traces, or you can have solder flux burned to carbon between the board traces.
You could also have a blown diode bridge, or a bad solder joint on it. This is part 431? The bridge you can measure out of circuit- one diode drop between either AC terminal and plus, between minus and both AC terminals. Check backwards too, you should get 9999 ohms backwards. The 15 v bridge is protected against an internally shorted diode with two 1k resistors series with the AC input. If one of these resistors is dropping the whole 16 VAC then either the bridge or something thereafter is shorted.
E-caps don't have to blow their tops to be defective. They are some of the most likely parts to fail after 5 to 15 years depending on the quality initially purchased. If your bridge has floppy wires on it, I'd unsolder that first.
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Well.. There's a led on both pre amp board, which is the "power on" led.. You'll see it from the outside. I was measuring the board with the functioning led, in which all rails seemed to be all right, and not the one with the led off, which is obviously the one with rail voltage problems ( as i said in post #46) .
Anyway, now i make you laugh even more, while i am crying.. I tested the "good" board with the speakers, to be sure that i was correct.. I didn't mount the heat dissipators, i tought for a couple of minutes it would have been ok without, and...... BOOM!
Wonderful grey shaded smoke out of the board... Mamma mia, f***in hell!
Result: i burned AT LEAST the two out transistors, maybe even something more, i have to check.
I feel a bit frustrated, instead of improving i'm damaging even more. But i wanna go trough it, it's a good school, isn't it?
I think i make an order of these transistors, the bridge rectifiers, the voltage regulators, the caps etc etc. So i virtually have the culprit, somewhere, and if not it's nice to have some spare parts.
Indianajo, i tested the bridge diode out if the board, which is a RS 205, it seems to be good, that is right voltage drops. I'll order a couple of them as well.
When you stop laughing at me, please drink a wine in my honour... I need positive vibrations right now!😀 (And a good tequila as well......)
Anyway, now i make you laugh even more, while i am crying.. I tested the "good" board with the speakers, to be sure that i was correct.. I didn't mount the heat dissipators, i tought for a couple of minutes it would have been ok without, and...... BOOM!
Wonderful grey shaded smoke out of the board... Mamma mia, f***in hell!
Result: i burned AT LEAST the two out transistors, maybe even something more, i have to check.
I feel a bit frustrated, instead of improving i'm damaging even more. But i wanna go trough it, it's a good school, isn't it?
I think i make an order of these transistors, the bridge rectifiers, the voltage regulators, the caps etc etc. So i virtually have the culprit, somewhere, and if not it's nice to have some spare parts.
Indianajo, i tested the bridge diode out if the board, which is a RS 205, it seems to be good, that is right voltage drops. I'll order a couple of them as well.
When you stop laughing at me, please drink a wine in my honour... I need positive vibrations right now!😀 (And a good tequila as well......)
which is why i mentioned a "dim bulb tester" earlier but what do i know...
i'll raise a scotch to the school of hard knocks for you chiunana!
i'll raise a scotch to the school of hard knocks for you chiunana!
Well, sorry about the transistors but now you know why heat sinks are important. Don't forget the tube of heat sink compound you will need it they were off. Often this kind of stuff you can salvage out of old PCAT power supplies or something, I've got several bridges from them and dozens of 1n5158 and bigger diodes. Those power supplies seem to blow up about every year, and they only cost $29 over hear, less than the part cost at retail.
I'd poke around with the 15 v ps area with a problem before I ordered anything. I only keep one bridge around, haven't used it yet. I don't have any 7815 7915 regulators, because nothing I own uses them. My projects are too old, mostly.
So you have the "bad board" with a +-15 v problem, and the other board with an output transistor problem. Labels are a real good idea now, since there is a problem with each. That is why shops tie "service tickets" to a project, to show what they know about a unit every time somebody works on one. Bread bag ties and a sharpie marker writing on folded over scotch tape will do for labels if you don't have something better.
I'd finish diagnosing the 15 v board, before I tried on the output transistor blown board. Then you can make one parts order and get everything you need in one $8 (freight) box. You'll also make any "minimum buy" limit probably.
When O.T.'s go, rail voltage often leaks out the base line and blows up other stuff before the output transistors. I replaced 104 parts in my most recent project, 84 more than the 20 output transistors that were bad or highly stressed. Hint-:when replacing output transistors, you have to replace all the ones on a channel, the new ones might be a different process than the old ones and the replacements won't match the old ones even if they have the same part number.
That 104 part project was a real learning project. I'm not done learning yet, I'm building a DC detection and shutoff circuit for it better than the one it came with (which didn't work properly).
If the bridge is good, how much voltage drop are you getting on the 1k resistors feeding the AC inputs? If >13 v is dropping on each or eitgher, the bridge is shorted or something after the bridge is shorted. If you have 4 clip leads you can install the bridge that way and look for the short some without putting it back (it might still be bad at 16v but okay under the meter's 2 test volts on the diode scale). When powered up look for the 0.6 v forwards voltage drop between the AC terminals and the plus and minus terminals of the bridge. If there is not one but you get a zero, a diode is shorted under 15 v stress.
I'd poke around with the 15 v ps area with a problem before I ordered anything. I only keep one bridge around, haven't used it yet. I don't have any 7815 7915 regulators, because nothing I own uses them. My projects are too old, mostly.
So you have the "bad board" with a +-15 v problem, and the other board with an output transistor problem. Labels are a real good idea now, since there is a problem with each. That is why shops tie "service tickets" to a project, to show what they know about a unit every time somebody works on one. Bread bag ties and a sharpie marker writing on folded over scotch tape will do for labels if you don't have something better.
I'd finish diagnosing the 15 v board, before I tried on the output transistor blown board. Then you can make one parts order and get everything you need in one $8 (freight) box. You'll also make any "minimum buy" limit probably.
When O.T.'s go, rail voltage often leaks out the base line and blows up other stuff before the output transistors. I replaced 104 parts in my most recent project, 84 more than the 20 output transistors that were bad or highly stressed. Hint-:when replacing output transistors, you have to replace all the ones on a channel, the new ones might be a different process than the old ones and the replacements won't match the old ones even if they have the same part number.
That 104 part project was a real learning project. I'm not done learning yet, I'm building a DC detection and shutoff circuit for it better than the one it came with (which didn't work properly).
If the bridge is good, how much voltage drop are you getting on the 1k resistors feeding the AC inputs? If >13 v is dropping on each or eitgher, the bridge is shorted or something after the bridge is shorted. If you have 4 clip leads you can install the bridge that way and look for the short some without putting it back (it might still be bad at 16v but okay under the meter's 2 test volts on the diode scale). When powered up look for the 0.6 v forwards voltage drop between the AC terminals and the plus and minus terminals of the bridge. If there is not one but you get a zero, a diode is shorted under 15 v stress.
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Hei, thanks for the answers.
I've got 15.9 V on both resistors. You mean 13 V as treshold 'cause of the 4 diodes voltage drop of the bridge rectifier, right? That would be a result of circa 2.4 V, though.
The transformer feeds with 16.2 V, to be exact.
I don't have 4 clips, unfortunately.
It's a good idea to make a bigger order, i don't have so much time, though, 'cause i need these speakers in a couple of weeks.
Btw i marked the boards now, another painful lesson...
I've got 15.9 V on both resistors. You mean 13 V as treshold 'cause of the 4 diodes voltage drop of the bridge rectifier, right? That would be a result of circa 2.4 V, though.
The transformer feeds with 16.2 V, to be exact.
I don't have 4 clips, unfortunately.
It's a good idea to make a bigger order, i don't have so much time, though, 'cause i need these speakers in a couple of weeks.
Btw i marked the boards now, another painful lesson...
If R32 & 33, the resistors between the transformer & the rectifier bridge, are dropping 15 v, something is seriously shorted thereafter. I'd start by pulling one end of the caps after off the board and see if that gets voltage on R32/33 back to a normal 1/2- 1 volt drop on those resistors.
Those resistors are there to prevent a short from blowing the transformer. You just lucked out the designers weren't saving every last penny to ****w the customer.
Those resistors are there to prevent a short from blowing the transformer. You just lucked out the designers weren't saving every last penny to ****w the customer.
well, thanks to the designer, then.. 🙂
i'll give it a try tonight, should i desolder one end of any cap or just one in general?
btw, i've found all the components in an italian shop (no farnell, mouser etc) for a really reasonable price. i can't find the RS205 though. before i go direction mouser, isn't there any equivalent i could use? google tells me NTE169. couldn't find it either on normal eBay circuit.
i'm not going to order before i know what i should buy, worst case scenario Mouser is always there, even though it has no italian warehouse, so it has to be shipped from US.
i prefer local market 😀
i'll give it a try tonight, should i desolder one end of any cap or just one in general?
btw, i've found all the components in an italian shop (no farnell, mouser etc) for a really reasonable price. i can't find the RS205 though. before i go direction mouser, isn't there any equivalent i could use? google tells me NTE169. couldn't find it either on normal eBay circuit.
i'm not going to order before i know what i should buy, worst case scenario Mouser is always there, even though it has no italian warehouse, so it has to be shipped from US.
i prefer local market 😀
C blob and C blob are right after the rectifier bridge and before the 7815/7915. I'd pull one end of those first. If that doesn't get the voltage drop on the resistors down, pull the ones after the 7815-7915. If that doesn't work pull the 7815 and 7915.
Electrolytic caps are very high on the list of parts that wear out in as low as a year in computer power supplies. Depends on what kind of **** they seal them with - are they sleazy 500 hour caps from retooled ********ists used to lying to the the production control bureau, or respected 10000 hour caps from nichicon, panasonic, rubicon, Vishay Sprague? In the early 1990's a company in taiwan flooded the world with **** caps, it seems the most respected vendors bought some. These would eat the lands of the PC board. Don't buy a roland 80 or 90 organ without a suffix. I know of a motor drive vendor (semi) that went out of business due to all the **** CDE electrolytic caps they installed in their drives. Three years and junk, with ooze leaking out of the case, all of them in the factory I worked at. A cold morning, the conveyor wouldn't start, pull the cover, look at the ooze, sit on the floor and start sawing bolts off the case. The story of my winters a couple of years.
Electrolytic caps are very high on the list of parts that wear out in as low as a year in computer power supplies. Depends on what kind of **** they seal them with - are they sleazy 500 hour caps from retooled ********ists used to lying to the the production control bureau, or respected 10000 hour caps from nichicon, panasonic, rubicon, Vishay Sprague? In the early 1990's a company in taiwan flooded the world with **** caps, it seems the most respected vendors bought some. These would eat the lands of the PC board. Don't buy a roland 80 or 90 organ without a suffix. I know of a motor drive vendor (semi) that went out of business due to all the **** CDE electrolytic caps they installed in their drives. Three years and junk, with ooze leaking out of the case, all of them in the factory I worked at. A cold morning, the conveyor wouldn't start, pull the cover, look at the ooze, sit on the floor and start sawing bolts off the case. The story of my winters a couple of years.
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Hi, i missed your answer, maybe i trashed the mail without my knowledge.. Sorry.
I ordered everything i need to repair these amps.. At least i hope so.
I made a bigger order, even with some basic tool (a good wire cutter and this kind of stuff) and i just bougt everything that could be damaged in these circuits, at Mouser.
It's ok to have some spare parts, important is to fix them.. I actually need them next week, i hope i can do it, i really hope so (for the marriage of a friend of mine).
Lets make a short summary:
1 speaker A
I shorted the outputs cause i did not screw the heat dissipators.
Channel 1 SEEMED to be ok, channel 2 totally distorted sound
2 speaker B
No rail on the pre/tone control board
I will continue writing down what i am doing and making questions. Anybody has to feel free to answer or not.. I'll be grateful to everybody, actually i already am 'cause i am really learning something up here.
Even the story of the electrolytics caps, indianajo, is incredible!
Btw, the ones i've got on the board are koshin.
I start with speaker A:
i replaced the 2 out transistor but the relay doesn't close and the amp does notgive any hint for activity. The transistor are getting warm, though.
There should be some other burned component. I would check transistors first. Do i have to desolder them necessarly?
I ordered everything i need to repair these amps.. At least i hope so.
I made a bigger order, even with some basic tool (a good wire cutter and this kind of stuff) and i just bougt everything that could be damaged in these circuits, at Mouser.
It's ok to have some spare parts, important is to fix them.. I actually need them next week, i hope i can do it, i really hope so (for the marriage of a friend of mine).
Lets make a short summary:
1 speaker A
I shorted the outputs cause i did not screw the heat dissipators.
Channel 1 SEEMED to be ok, channel 2 totally distorted sound
2 speaker B
No rail on the pre/tone control board
I will continue writing down what i am doing and making questions. Anybody has to feel free to answer or not.. I'll be grateful to everybody, actually i already am 'cause i am really learning something up here.
Even the story of the electrolytics caps, indianajo, is incredible!
Btw, the ones i've got on the board are koshin.
I start with speaker A:
i replaced the 2 out transistor but the relay doesn't close and the amp does notgive any hint for activity. The transistor are getting warm, though.
There should be some other burned component. I would check transistors first. Do i have to desolder them necessarly?
EDIT
i found a couple of damaged fuses.. Therefore it doesn't turn on. Got to wait until tomorrow morning to get new ones..
i found a couple of damaged fuses.. Therefore it doesn't turn on. Got to wait until tomorrow morning to get new ones..
The amp I bought with 19 out of 20 output transistors blown, a lot of OT emitter resistors were blown too. 3 out of 4 drivers were blown, etc. Those other things you can check with an ohmmeter function of the DVM.
I see.
On power board A (i remind, the one with burned outs i replaced) it keeps burning the F1 fuse (6.3 A) whenever i turn the amp on.
I assume that some other transistor AFTER the fuse is blown, so that the circuit demands for full rail voltage. Am i correct or is there any other scenario?
On power board A (i remind, the one with burned outs i replaced) it keeps burning the F1 fuse (6.3 A) whenever i turn the amp on.
I assume that some other transistor AFTER the fuse is blown, so that the circuit demands for full rail voltage. Am i correct or is there any other scenario?
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