i think i have a similar amp at home, I was supose to fix it for friend amp this one also hadde a blown channel but i gav up after several hours of work....
I think a still have it store som where. if i don't remmeber wrong I think it was a 1080
dont hesitate to take contact if you need some more help...
I think a still have it store som where. if i don't remmeber wrong I think it was a 1080
dont hesitate to take contact if you need some more help...
Hello!
I have now been resting from this amp for a couple of weeks.
After cleaning the entire board with flux-off print-circuit cleaning
the board shines like new.
I have replaced ALL audio-amp transistors (execept TR515,516)
forgott to order them.
But they check OK out of the board and i really dont think they are defective.
I also replaced ALL Elyts on the amp board. (except the 4 bigger
expensive ones. )
I have replaced some diodes that shorted (ZD503,501 D509, 507)
during the last tests. Seemes like the transistor replacements
solved the oscillation problem. (Have only confirmed that with
scope on one of point but Before I Replaced the transistors
i had a oscillation that really messed up the Diodes.
Now to my problem! R529, R530 gets REALLY hot after only
10 seconds. And TR509,510,511,512 are also getting varm.
Not to the degree that it will hurt them if i only power the
amp to measure but if i run it for some minutes im not sure
how the will handle the heat (current).
I should also say that the 4 OUTPUTS are removed.
(this should not be a problem??)
Everything else are as it should be, all components and
connections and everything.
VR501,502,503,504 are fully counter clockwise.
(tryed to place them in center position but then the
resistors heated upp even faster.)
The manual says turn them fully clockwise and in 10 seconds
from powering upp the DC offset should be sett to ~8mV.
(you have to read the page do understand i think!)
From here what should i check? I am not sure that the
trimpots are OK.
But i remember measuring them OK some weeks ago.
And defective for both channels?
You should never say never buth i really dont think they are
faulty 😉
Any kind of help is welcome!
I have now been resting from this amp for a couple of weeks.
After cleaning the entire board with flux-off print-circuit cleaning
the board shines like new.
I have replaced ALL audio-amp transistors (execept TR515,516)
forgott to order them.
But they check OK out of the board and i really dont think they are defective.
I also replaced ALL Elyts on the amp board. (except the 4 bigger
expensive ones. )
I have replaced some diodes that shorted (ZD503,501 D509, 507)
during the last tests. Seemes like the transistor replacements
solved the oscillation problem. (Have only confirmed that with
scope on one of point but Before I Replaced the transistors
i had a oscillation that really messed up the Diodes.
Now to my problem! R529, R530 gets REALLY hot after only
10 seconds. And TR509,510,511,512 are also getting varm.
Not to the degree that it will hurt them if i only power the
amp to measure but if i run it for some minutes im not sure
how the will handle the heat (current).
I should also say that the 4 OUTPUTS are removed.
(this should not be a problem??)
Everything else are as it should be, all components and
connections and everything.
VR501,502,503,504 are fully counter clockwise.
(tryed to place them in center position but then the
resistors heated upp even faster.)
The manual says turn them fully clockwise and in 10 seconds
from powering upp the DC offset should be sett to ~8mV.
(you have to read the page do understand i think!)
From here what should i check? I am not sure that the
trimpots are OK.
But i remember measuring them OK some weeks ago.
And defective for both channels?
You should never say never buth i really dont think they are
faulty 😉
Any kind of help is welcome!
Please! Someone, i need help 😉
What should i do to find the cause of the "over" current flowing
trought the resistors and transistors mentioned above?
can it have something with the trimpots to do?
been looking at this amp for so long that im almosty blind
now.
can it have something to do that the outputs are not in place?
(drivers are mounted where they should be TR519,520,521,522)
I am in big need of advice =)
What should i do to find the cause of the "over" current flowing
trought the resistors and transistors mentioned above?
can it have something with the trimpots to do?
been looking at this amp for so long that im almosty blind
now.
can it have something to do that the outputs are not in place?
(drivers are mounted where they should be TR519,520,521,522)
I am in big need of advice =)
You're working inside the feedback loop so all components need to be in the circuit. After you reinstall the outputs, you need to measure the voltage at the various points shown in the circuit to determine where the problem lies.
If the amp is blowing outputs, install 1 amp fuses in series with the emitter resistors. That 'should' protect the output transistors. Set the bias pot to the minimum as a starting point.
If the amp is blowing outputs, install 1 amp fuses in series with the emitter resistors. That 'should' protect the output transistors. Set the bias pot to the minimum as a starting point.
okay i will try that! is it ok to measure with a 60W bulb in series
with AC?
I noticed that i only have around 42 volts from the 56 volt
supply, but this is because i fitted the bulb? i think..
wich is the most important points to measure?
Should i start measuring the outputs or should i start with the
intputs.
can i get good readings according to schematic with the
60W bulb?
I will only power it for max 5 seconds, with clip leads
and write down the measurements.
Both channels have the same symtoms...
i am going to replace the trimpots today measured them yesterday and i cant say i have confidence in them.
Last time i fitted the outputs the amp jumped 5 inches of the
table 😛
with AC?
I noticed that i only have around 42 volts from the 56 volt
supply, but this is because i fitted the bulb? i think..
wich is the most important points to measure?
Should i start measuring the outputs or should i start with the
intputs.
can i get good readings according to schematic with the
60W bulb?
I will only power it for max 5 seconds, with clip leads
and write down the measurements.
Both channels have the same symtoms...
i am going to replace the trimpots today measured them yesterday and i cant say i have confidence in them.
Last time i fitted the outputs the amp jumped 5 inches of the
table 😛
You can measure the voltage with the lamp in series.
Yes, the lamp will reduce the supply voltage.
To prevent the outputs from being biased on, short the bases of the driver transistors together. When you power it up, do so for a few seconds at a time until you're sure that nothing is going to overheat. If a component overheats, let us know which one it is.
The voltages will not be the same as they would be at full line voltage but they should tell us where the problem is. When you get it up and running, post the voltages at 10 different points in the circuit. Include the transistor number and the leg from which you read the voltage.
Are the insulators between the output transistors and the sink intact?
Yes, the lamp will reduce the supply voltage.
To prevent the outputs from being biased on, short the bases of the driver transistors together. When you power it up, do so for a few seconds at a time until you're sure that nothing is going to overheat. If a component overheats, let us know which one it is.
The voltages will not be the same as they would be at full line voltage but they should tell us where the problem is. When you get it up and running, post the voltages at 10 different points in the circuit. Include the transistor number and the leg from which you read the voltage.
Are the insulators between the output transistors and the sink intact?
I have done some measuring with my textronic scope.
I did not have the outputs in place (taught i orderd them some
weeks ago but that was not the case)
The <.0 means that within 2 seconds the voltage is near zero.
30<.0 means that from 30V within 2 seconds the voltage is near zero from powering on.
Still TR509.510.511.512 gets really hot in within 10 seconds!
R529, R530 gets really hot to!
TR505 E14 C30 B14
TR506 E14 C30 B14
TR507 E14 C30 B12
TR508 E14 C30 B14
TR509 E30 C1 B30
TR511 E30 C1 B30
TR510 E30 C1 B30
TR512 E30 C1 B30
TR513 E1 C1 B1
TR514 E1 C1 B0
TR515 E0.5 C15<.0 B1V
TR516 E0.5 C15<.0 B1V
TR517 E10<.0 C10<.0 B10<.0
TR518 E10<.0 C10<.0 B10<.0
TR519 E30<.0 C45 B30<.0
TR520 E30<.0 C45 B30<.0
TR521 E30<.0 C-45 B30<.0
TR522 E30<.0 C-45 B30<.0
Hope you can help me analyze the voltages 🙂
i just cant understand some of the voltages...
remember that i replaced all these transistors except 515.516
wich i have measured OK!
I did not have the outputs in place (taught i orderd them some
weeks ago but that was not the case)
The <.0 means that within 2 seconds the voltage is near zero.
30<.0 means that from 30V within 2 seconds the voltage is near zero from powering on.
Still TR509.510.511.512 gets really hot in within 10 seconds!
R529, R530 gets really hot to!
TR505 E14 C30 B14
TR506 E14 C30 B14
TR507 E14 C30 B12
TR508 E14 C30 B14
TR509 E30 C1 B30
TR511 E30 C1 B30
TR510 E30 C1 B30
TR512 E30 C1 B30
TR513 E1 C1 B1
TR514 E1 C1 B0
TR515 E0.5 C15<.0 B1V
TR516 E0.5 C15<.0 B1V
TR517 E10<.0 C10<.0 B10<.0
TR518 E10<.0 C10<.0 B10<.0
TR519 E30<.0 C45 B30<.0
TR520 E30<.0 C45 B30<.0
TR521 E30<.0 C-45 B30<.0
TR522 E30<.0 C-45 B30<.0
Hope you can help me analyze the voltages 🙂
i just cant understand some of the voltages...
remember that i replaced all these transistors except 515.516
wich i have measured OK!
You'll need to install the outputs before you can come to any conclusions.
While waiting on the outputs, determine why the emitters of TR515 and TR516 aren't near the negative rail.
While waiting on the outputs, determine why the emitters of TR515 and TR516 aren't near the negative rail.
okay i trust you when youre saying that i must have
the outputs in place.
i just cant understand Why? I see the feedback loop going
back to the input fets.
do you know some good literature wich explains feedback
loops differential amps and so on? i just want to learn..
and the only cause i can think off is a break in the copper.
i meand tr 515,516 is directly connected to the negative rail.
what other cause can it be? :S
the outputs in place.
i just cant understand Why? I see the feedback loop going
back to the input fets.
do you know some good literature wich explains feedback
loops differential amps and so on? i just want to learn..
and the only cause i can think off is a break in the copper.
i meand tr 515,516 is directly connected to the negative rail.
what other cause can it be? :S
PROGRESS!!! 😉 =)
R534 was open... FR must be Fuse-Resistor?
can i use any "kole" material resistor?
because they always open when failing.
cant find anything that says "fusable-resistor" at my
local shop... elfa.se....
never had the taught of a simple thing like this.
is it just stupid to put an ordinary 1/2W resistor
here for testing and measuring?
R534 was open... FR must be Fuse-Resistor?
can i use any "kole" material resistor?
because they always open when failing.
cant find anything that says "fusable-resistor" at my
local shop... elfa.se....
never had the taught of a simple thing like this.
is it just stupid to put an ordinary 1/2W resistor
here for testing and measuring?
It's not safe to use a standard resistor. Sometimes, standard resistors can produce significant flames when they fail. You have to wait on the outputs. Get the proper resistors.
Yes, they are fusible resistors. These are slightly different than flameproof (BR). Be sure to get the correct type. Typically, fusible resistors have a black band as the last band.
There's no point in measuring anything else until you get the outputs. Inside the feedback loop, you have to have a complete loop (all components in the circuit) for the voltages to be correct.
Yes, they are fusible resistors. These are slightly different than flameproof (BR). Be sure to get the correct type. Typically, fusible resistors have a black band as the last band.
There's no point in measuring anything else until you get the outputs. Inside the feedback loop, you have to have a complete loop (all components in the circuit) for the voltages to be correct.
R519,520,521,522 was open!!!
R531,532,533,534 also!!!
Nice feeling of progress!
Right channel i have a oscillation about 10V peak-peak
very high freuquency....
and Left channel have 5 volts on the Base of the
outputs!!! :S cant adjust it with the pots..
This is similar to the original problem i had some time ago..
R531,532,533,534 also!!!
Nice feeling of progress!
Right channel i have a oscillation about 10V peak-peak
very high freuquency....
and Left channel have 5 volts on the Base of the
outputs!!! :S cant adjust it with the pots..
This is similar to the original problem i had some time ago..
Hello perry!
no i dont have the outputs.
i should be able to adjust the bias with the pot
but when i turn it nothing happens, and i checked the
pot yesterday.
for the other channel wich is oscillating 10v peak-peak
on the bases of the outputs see a change when turning
pot.
but the onther channel is 5 volts rock steady.
if i mount outputs they would crossconduct and make
a real mess 😛 i mean 5 volts!? it would turn them fully open...
whyis just one channel oscillating :S no differense if i
disconnect the input cord from the input card :S
no i dont have the outputs.
i should be able to adjust the bias with the pot
but when i turn it nothing happens, and i checked the
pot yesterday.
for the other channel wich is oscillating 10v peak-peak
on the bases of the outputs see a change when turning
pot.
but the onther channel is 5 volts rock steady.
if i mount outputs they would crossconduct and make
a real mess 😛 i mean 5 volts!? it would turn them fully open...
whyis just one channel oscillating :S no differense if i
disconnect the input cord from the input card :S
Without the outputs, it's very difficult to know what to expect.
I recommended jumping between the bases of the driver transistor bases and inserting the 1 amp fuses in series with the emitter resistors to protect the outputs. If you do this, the bias voltage will be 0 and the outputs will not be able to turn on. With the jumper in place, the output may not be 100% stable (may have a bit of oscillation) but it should allow you to safely troubleshoot the circuit.
The voltage may be at 5v because the differential amplifier is trying to compensate for an offset. The ±0.6v at the bases of the outputs may not necessarily be ±0.6v without the outputs in place.
Except for checking every part in the circuit, there's no way to troubleshoot it without the outputs in the circuit.
I recommended jumping between the bases of the driver transistor bases and inserting the 1 amp fuses in series with the emitter resistors to protect the outputs. If you do this, the bias voltage will be 0 and the outputs will not be able to turn on. With the jumper in place, the output may not be 100% stable (may have a bit of oscillation) but it should allow you to safely troubleshoot the circuit.
The voltage may be at 5v because the differential amplifier is trying to compensate for an offset. The ±0.6v at the bases of the outputs may not necessarily be ±0.6v without the outputs in place.
Except for checking every part in the circuit, there's no way to troubleshoot it without the outputs in the circuit.
ok but nomatter what. if the diff amp is trying
to compensate for an offset i still should be able
to adjust the bias voltage slightly?
and the Zener is just making it better because
it is a 5.1 zener not allowing the bias voltage to rise
above volts :S so maybe i have 10 volts. or 50 volt
i dont know.. have to check and measure..
something is really wrong in the bias circuit for the
one channel...
just waiting for my outputs =)
to compensate for an offset i still should be able
to adjust the bias voltage slightly?
and the Zener is just making it better because
it is a 5.1 zener not allowing the bias voltage to rise
above volts :S so maybe i have 10 volts. or 50 volt
i dont know.. have to check and measure..
something is really wrong in the bias circuit for the
one channel...
just waiting for my outputs =)
still making progress =) the biasing diod c1815 are shorted
base to collector. not good. that explains why i have
5 volts on the bases of the outputs!
base to collector. not good. that explains why i have
5 volts on the bases of the outputs!
God news and Bad news !
The good news is after fitting some new outputs in the right
channel.
I tested the amp and it worked fine!!
Oscillation dissapeard... and the voltage looked good
on the base of the outputs.
But the sound was crappy.. very low output (tested with
a subwoofer) and it started clipping very early when
turning the volume upp.
But i adjusted the bias pot to 8mV....
And then i taught that maybe its because i have the lamp
in series with AC wich is making the sound very awfully.
After checking that NOTHING got overheated i plugged the
amp in without the lamp.
No change in sound.... but after some seconds the fuse
blew (the AC fuse before the torrido)....
Some weeks ago i put an 2,5Amp instead of an 4amp wich it should be just in case.
i found D507 and ZD501 was shorted now... 🙁
And TR525, TR527 (outputs) was shorted also....
STRANGE??? 525 is on the negative rail and 527 on the positive.
And the only diodes shorted are D507 ZD501 which are on
the positive side...
TR519 520 are OK!
Any ideas why ?? 3 steps forward and 2 backwards 😛
The good news is after fitting some new outputs in the right
channel.
I tested the amp and it worked fine!!
Oscillation dissapeard... and the voltage looked good
on the base of the outputs.
But the sound was crappy.. very low output (tested with
a subwoofer) and it started clipping very early when
turning the volume upp.
But i adjusted the bias pot to 8mV....
And then i taught that maybe its because i have the lamp
in series with AC wich is making the sound very awfully.
After checking that NOTHING got overheated i plugged the
amp in without the lamp.
No change in sound.... but after some seconds the fuse
blew (the AC fuse before the torrido)....
Some weeks ago i put an 2,5Amp instead of an 4amp wich it should be just in case.
i found D507 and ZD501 was shorted now... 🙁
And TR525, TR527 (outputs) was shorted also....
STRANGE??? 525 is on the negative rail and 527 on the positive.
And the only diodes shorted are D507 ZD501 which are on
the positive side...
TR519 520 are OK!
Any ideas why ?? 3 steps forward and 2 backwards 😛
The rail voltage was probably low when you had the lamp in series. If you adjusted the bias current with low rail voltage, the bias may have increased significantly when the rail voltage increased (when you removed the lamp). That may have been enough to cause the failure of the outputs.
Okay you learn by misstakes 😉
but they was not cheap the outputs! 😛
have to fit some new ones and see if i still
have the same problem with crappy sound and low
output.
feels like it was poor quality because the lamp did not
even glow bright before the diodes shorted and
the outputs shorted.
Maybe he sold me fakes and took my precious money :S
But i really trust that old man so maybe not....
Is there some other way to set the bias?
According to service manual i should set the bias to
8mV (with VR501)...
And then... i should apply a 1KHz 10mVrms test tone to
both channels and adjust the bias to 30mV with VR503.
I dont have a tone generator 🙁
Maybe i could do it with my computer??
I have a sinegenerator on it... freeware 🙂
but they was not cheap the outputs! 😛
have to fit some new ones and see if i still
have the same problem with crappy sound and low
output.
feels like it was poor quality because the lamp did not
even glow bright before the diodes shorted and
the outputs shorted.
Maybe he sold me fakes and took my precious money :S
But i really trust that old man so maybe not....
Is there some other way to set the bias?
According to service manual i should set the bias to
8mV (with VR501)...
And then... i should apply a 1KHz 10mVrms test tone to
both channels and adjust the bias to 30mV with VR503.
I dont have a tone generator 🙁
Maybe i could do it with my computer??
I have a sinegenerator on it... freeware 🙂
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