Good afternoon,
I haven’t used this amp of mine for about 15 years, but decided recently to bring it back to life.
The rca jacks had crumbled (as they apparently do) , so I replaced them.
Unfortunately I then noticed something. Brown and crumbly resistors are not a good look.
The parts I can track down via the schematics that other members have kindly posted, and I’m happy to replace them.
My concern is ....why would it happen???? and what else should I check before I hurl 220v through it all?
(I’m not an electronics guy, but I can wield a multimeter)
Thanks!
I haven’t used this amp of mine for about 15 years, but decided recently to bring it back to life.
The rca jacks had crumbled (as they apparently do) , so I replaced them.
Unfortunately I then noticed something. Brown and crumbly resistors are not a good look.
The parts I can track down via the schematics that other members have kindly posted, and I’m happy to replace them.
My concern is ....why would it happen???? and what else should I check before I hurl 220v through it all?
(I’m not an electronics guy, but I can wield a multimeter)
Thanks!
Attachments
Overheating has taken place at one time judging by the brown coloring of the PCB ,once heated to a certain temperature resistors can deteriorate due change in chemical construction and reaction over time .
I would check the value of the resistors in and around the burnt areas.
The resistor on the RHS of your photo has transistors (BJT,s ) near it I would check if they still function or are s/c (short circuit ).
Please don't rush in to power it up till you are sure the components are okay otherwise like some posters here who ask for help with a burnt out amplifier you will end up "frying " most of the components.
I would check the value of the resistors in and around the burnt areas.
The resistor on the RHS of your photo has transistors (BJT,s ) near it I would check if they still function or are s/c (short circuit ).
Please don't rush in to power it up till you are sure the components are okay otherwise like some posters here who ask for help with a burnt out amplifier you will end up "frying " most of the components.
Always use a DBT (dim bulb tester) for powering up something like this. It just saves so much grief from things going pop.
You need to reference those burnt parts to the circuit to see what has actually gone up and then try and decide 'why' that happened.
The other areas of discolouration could be (and often are) just down to heat reacting with the board material although ultimately you could argue the design and or rating of parts is suspect for something like to happen.
You need to reference those burnt parts to the circuit to see what has actually gone up and then try and decide 'why' that happened.
The other areas of discolouration could be (and often are) just down to heat reacting with the board material although ultimately you could argue the design and or rating of parts is suspect for something like to happen.
Those are burnt, period. 🙁
Please post said schematic here.
You have significant damage there, the transistor directly connected to them is most probably burnt/shorted, wouldn´t be surprised at amplifier blowing fuses since that is a power transistor.
I would definitely NOT connect it to mains unless through a Bulb Limiter, suggest 60W bulb, 75W tops.
You will have to troubleshoot and repair the amplifier; if you find that hard to do or inconvenient I suggest a Tech does it.
Do not "hurl" 220V but use a bulb limiter.
This does not look like a long steady deterioration but a violent event, getting red hot (or almost) and even catching fire in seconds.
Probably a mains fuse blew and stopped the amp from catching fire or at least damaging the power transformer.
You missed out------quote--"once heated to a certain temperature" -IE= overheated .
Once overheated continuing deterioration will take place over a long period of time---seems like 15 years is a long time .
Once overheated continuing deterioration will take place over a long period of time---seems like 15 years is a long time .
Thank you all.
So... once I’ve checked the diode for a short circuit, tracked down the resistors for the amp (and built myself a Dim 100w bulb tester.. looked them up - very straight forward) and replaced those. We should be good.
It wouldn’t surprise me if a mains fuse had blown.
There are a couple of other areas where the pcb has discoloured. But YouTube and forums suggest that these amps run hot anyway.
If you can think of any other things to check, your wise advice would be appreciated.
So... once I’ve checked the diode for a short circuit, tracked down the resistors for the amp (and built myself a Dim 100w bulb tester.. looked them up - very straight forward) and replaced those. We should be good.
It wouldn’t surprise me if a mains fuse had blown.
There are a couple of other areas where the pcb has discoloured. But YouTube and forums suggest that these amps run hot anyway.
If you can think of any other things to check, your wise advice would be appreciated.
Not by a country mile 🙁
Those resistors burnt (NOT "slowly degraded" , look at the burnt (not toasted) paint flakes well separated from resistor body, which means something else failed catastrophiclly first.
Again, I much suspect the attached power transistor, nor discarding other semiconductors.
"Looking healthy" proves nothing in the semiconductor world.
You still don't get it do you ??
Translation =
1-I said they overheated
2-having repaired old valve wirelesses that burnt out the series carbon resistor between the reservoir capacitor and the smoothing capacitor 20/30/40 years ago and the radio left to rot I know what a burnt out resistor looks like .
3- after years of being burnt out the burnt parts-----deteriorate ---set something flammable on fire -leave for 15 years are you saying zero extra deterioration does NOT take place if so what patent have you got it must be worth a fortune.
Translation =
1-I said they overheated
2-having repaired old valve wirelesses that burnt out the series carbon resistor between the reservoir capacitor and the smoothing capacitor 20/30/40 years ago and the radio left to rot I know what a burnt out resistor looks like .
3- after years of being burnt out the burnt parts-----deteriorate ---set something flammable on fire -leave for 15 years are you saying zero extra deterioration does NOT take place if so what patent have you got it must be worth a fortune.
Ok. I will check everything that I can see.
I was only wondering if anyone could shine me more light as to why or how THOSE resistors burnt out! Please forgive any ignorance on my part.
I was only wondering if anyone could shine me more light as to why or how THOSE resistors burnt out! Please forgive any ignorance on my part.
So you saying the those 2 resistors inside that black area overheated ?
Most likely they burned after the output power transistor failed.
For last I would ask you to show me a 8000a amplifier (or any other) with the same age without board discolouration around resistors and i don't mean burned out ones like in that picture.
For DRM Brun don't take me wrong but if you can't figure out what caused the burned resistors I would suggest handing the amp to someone that knows what they doing the 8000a is a very nice amp and worth saving.
Most likely they burned after the output power transistor failed.
For last I would ask you to show me a 8000a amplifier (or any other) with the same age without board discolouration around resistors and i don't mean burned out ones like in that picture.
For DRM Brun don't take me wrong but if you can't figure out what caused the burned resistors I would suggest handing the amp to someone that knows what they doing the 8000a is a very nice amp and worth saving.
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I think we have a linguistics problem here ---overheating --The Free Dictionary =
To HEAT too much .
Noun 1-overheating ---meltdown ,nuclear meltdown -severe overheating of the core of a nuclear reactor resulting in the core MELTING .
If a PCB ends up with blackened/brown marks on the PCB due to components --usually resistors under NORMAL use I would question the design engineers choice of components .
Never came across this in good quality amplifier designs it means profit came before safety margins and IMHO does the original designer no favours.
To HEAT too much .
Noun 1-overheating ---meltdown ,nuclear meltdown -severe overheating of the core of a nuclear reactor resulting in the core MELTING .
If a PCB ends up with blackened/brown marks on the PCB due to components --usually resistors under NORMAL use I would question the design engineers choice of components .
Never came across this in good quality amplifier designs it means profit came before safety margins and IMHO does the original designer no favours.
Just looking at the picture, the resistors on the left look like they run hot as the PCB has discoloured brown. This might be normal.
However the resistors on the right are failing or have failed.
You have 2 channels to compare against, assuming the other channel is still fine. You can use this to measure between the good and bad channel.
However the resistors on the right are failing or have failed.
You have 2 channels to compare against, assuming the other channel is still fine. You can use this to measure between the good and bad channel.
Not going into that discussion because I (we) don't know what caused that failure and DRM Brun didn't mention it but it looks like an output device failure.
I have seen worse actually I have seen amps catching fire in operation after a short on the speaker wires.
I have seen worse actually I have seen amps catching fire in operation after a short on the speaker wires.
"Normal " not in my book but 1 watt (or higher ) resistors are pennies dearer and add up in a production line of 1000,s to a substantial amount obviously there was a profit motive if it was the boardroom decision and not a audio design engineers decision.
Show me one power amp design in EW by the well known audio designers where component design wasn't taken into consideration ?
I know D.self or JLH take great care on this issue so much so that they published articles on it .
Show me a D.Self design that has overheating resistors as standard allowing a browning/blackening of the PCB.
Show me one power amp design in EW by the well known audio designers where component design wasn't taken into consideration ?
I know D.self or JLH take great care on this issue so much so that they published articles on it .
Show me a D.Self design that has overheating resistors as standard allowing a browning/blackening of the PCB.
A hot resistor may not be overheating. Over many years of use it may cause discolouration of the PCB, but that does not mean the resistor is being pushed past its specification. Resistor colour on the left in that photo looks normal.
You see designs where the resistor is mounted floating/with long legs to mitigate the problem.
On real world cost driven electronic design, cost vs specification is important, if you want to make a profit. But running a resistor hot may not be a problem, even if the end results are not that pretty.
To DRM Brun check everything from the output on that channel starting on the output inductor (if there is one, don't remember) power transistor(s) drive transistors and everything else associated with that channel until you happy that nothing else is broken.
In the end don't forget to adjust the idle current (Bias).
Good luck
In the end don't forget to adjust the idle current (Bias).
Good luck
You do know the electrical design characteristics of an overheating or even hot resistor on the amount of random electron flow in that resistor due to heat ?
If its hot enough to brown a PCB then its creating noise no matter what the original spec. is.
Heard of thermal noise generators using resistors ?
Resistor Noise » Resistor Guide
Also (a bit more technical )-
E4_Lad_N.pdf
If its hot enough to brown a PCB then its creating noise no matter what the original spec. is.
Heard of thermal noise generators using resistors ?
Resistor Noise » Resistor Guide
Also (a bit more technical )-
E4_Lad_N.pdf
Nice post, but not sure how it relates to DRM Brun's original question. (Plus the technical paper conclusion is you can measure the noise difference, not how it will actually impact a real design, pretty low level noise in any case).
As before a hot running resistor, i.e. the ones on the left, may be normal. Burnt ones, as on the right, are not.
To DRM Brun, with 2 channels you can measure between the 2 channels, assuming you have a working channel. Resistance measurements on resistors, and diode measurements on any diodes and transistors may show the problem part if something is wrong, without having to apply power.
As before a hot running resistor, i.e. the ones on the left, may be normal. Burnt ones, as on the right, are not.
To DRM Brun, with 2 channels you can measure between the 2 channels, assuming you have a working channel. Resistance measurements on resistors, and diode measurements on any diodes and transistors may show the problem part if something is wrong, without having to apply power.
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Have you even LOOKED at the picture?😱
Wev are not talking "old valve wireless" receivers here, and your example most certainly used carbon composition resistors, a very different beast, including how they burn.
THOSE can crumble along time, since they are made out of carbon DUST, held together with a binder.
These are carbon FILM resistors (maybe even metal film), absolutely different, so whatever you knew about the old ones does not apply here.
Besides, I have seen and replaced tens of thousands of burnt carbon film resistors, and they match what´s on the picture.
Which kind of resistor?
Not these.
Poor attempt at sounding witty 😀
And not what I said, of course.
So far at least two or three of us are pointing at highly suspect or burnt power transistor, the one shown on top of the burnt resistors.
You certainly do. 😀
Comparing a Hi Fi amplifier to Three Mile Island, Fukushima or Chernobyl certainly sounds like a little bit of overstretch to me.
Oh well.