I'm doing some required 'maintenance' on the front-right channel the amp board in this unit.
Transistors were shorted, resistors were fried.
Replacing the PNP/NPN resistors without the bias transistor, I couldn't get the idling current below 100mV. So, I am replacing that and also replacing the transistors again because they are way out of range of what the rest of the transistors read.
What is a good temperature to see these transistors at? I registered 150°+ F (60-70C) with no volume (HEOS is paused).
First question: Should I be looking at other resistors to make sure they are in range or is that a normal operating temperature?
Second question: Other than Lead-free, what other properties should I have with my solder. (Size, Flux core)? T
The first time didn't come out with any perfection at all, I would like to make sure this time looks better.
Transistors were shorted, resistors were fried.
Replacing the PNP/NPN resistors without the bias transistor, I couldn't get the idling current below 100mV. So, I am replacing that and also replacing the transistors again because they are way out of range of what the rest of the transistors read.
What is a good temperature to see these transistors at? I registered 150°+ F (60-70C) with no volume (HEOS is paused).
First question: Should I be looking at other resistors to make sure they are in range or is that a normal operating temperature?
Second question: Other than Lead-free, what other properties should I have with my solder. (Size, Flux core)? T
The first time didn't come out with any perfection at all, I would like to make sure this time looks better.
Quick thought on bias current... some circuits are quite dependent on the characteristics of the transistors used and replacements can be significantly different, enough to force bias out of range' Usually a simple tweak of the resistor values in the vbe multiplier is all that is needed.
Make sure the transistors you fit are genuine devices from authorised distributers as there are numerous fake parts around.
I would not recommend lead free solder for general hobbyist/diy work, just stick to a good 60/40 type intended for rework and repair.
The temperature of the output transistors will be determined automatically by the correct bias current and voltage across them. 60-70C is way to hot for normal idling of a typical amp.
Make sure the transistors you fit are genuine devices from authorised distributers as there are numerous fake parts around.
I would not recommend lead free solder for general hobbyist/diy work, just stick to a good 60/40 type intended for rework and repair.
The temperature of the output transistors will be determined automatically by the correct bias current and voltage across them. 60-70C is way to hot for normal idling of a typical amp.
It says PB free solder everywhere on the board and service manual, wouldn't you stick with that?
So, those idle temps are too high, I presume it's time to check all the resistors for the ones with high temp transistors?
And, yes, I ordered the right ones from a Denon distributor this time, not skimping out with anything.
So, those idle temps are too high, I presume it's time to check all the resistors for the ones with high temp transistors?
And, yes, I ordered the right ones from a Denon distributor this time, not skimping out with anything.
Stuff has been lead free for years but it is not always the easiest solder to work with. Conventional solder melts more easily (at lower temperature) and can flow better. Leaded solder needs a suitable iron (for the temperatures involved) and more care in tinning and preparing component leads.
If the idle current adjusts but will not adjust low enough then you might need to alter a resistor value in the vbe multiplier to bring it in range. As always we would need to circuit details.
If the idle current adjusts but will not adjust low enough then you might need to alter a resistor value in the vbe multiplier to bring it in range. As always we would need to circuit details.
https://www.manualslib.com/manual/2798277/Denon-Avr-X4500h.html?page=41#manual
On page 41, you should get the details you would need to give me the resistor to replace. Thank you so much for this.
Edit: I just checked it, and yes, it adjusts. Can get it to 114mV (8.0 ± .3 is acceptable)
Just have to let you know though, the bias transistor is way out of spec from the rest of the bias transistors on this amp board or the other amp board; and it's already ordered. 🙂
Although, the heated ones (60-70°C) are ones I haven't touched before and have no issue with idle voltage.
What width should I use for the solder? .6mm?
On page 41, you should get the details you would need to give me the resistor to replace. Thank you so much for this.
Edit: I just checked it, and yes, it adjusts. Can get it to 114mV (8.0 ± .3 is acceptable)
Just have to let you know though, the bias transistor is way out of spec from the rest of the bias transistors on this amp board or the other amp board; and it's already ordered. 🙂
Although, the heated ones (60-70°C) are ones I haven't touched before and have no issue with idle voltage.
What width should I use for the solder? .6mm?
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To bring the bias current down you need to EITHER decrease R7124 or increase R7126. I can't give you specific values as they can not be calculated as that value depends on the transistors themselves. Just try the next resistor value up or down in the series.
Solder is personal preference. If you use thin you need metres of the stuff for anything large like transistors. I'm happy with 1 or 1.2 mm for most things. Its up to you though.
If the output transistors had failed then you need to be sure there is no other damage such as driver transistors or any of the low value resistors around that might have been damaged. Don't under estimate what is needed to fix something like this. If you are using genuine and correct manufacturer supplied parts then it should really all set up correctly without any modification.
Solder is personal preference. If you use thin you need metres of the stuff for anything large like transistors. I'm happy with 1 or 1.2 mm for most things. Its up to you though.
If the output transistors had failed then you need to be sure there is no other damage such as driver transistors or any of the low value resistors around that might have been damaged. Don't under estimate what is needed to fix something like this. If you are using genuine and correct manufacturer supplied parts then it should really all set up correctly without any modification.
Working on Front Right, but they all coalesce.
Q7231, Q7232 and, Q7225 will be replaced (tomorrow) with authentic Denon products this time. I will let you know it works and if I need more help.
R7231 R7232, R7233, R7234, R7229 and, R7230 were just replaced with Authentic Denon products.
On the hot ones, what would you suggest I check? I'm guessing the resistors you just mentioned would be important.
Can you please tell me where the driver transistors are? I have a guess but don't want to get it wrong.
Again, thanks for the assistance. Very nice of you to help
Q7231, Q7232 and, Q7225 will be replaced (tomorrow) with authentic Denon products this time. I will let you know it works and if I need more help.
R7231 R7232, R7233, R7234, R7229 and, R7230 were just replaced with Authentic Denon products.
On the hot ones, what would you suggest I check? I'm guessing the resistors you just mentioned would be important.
Can you please tell me where the driver transistors are? I have a guess but don't want to get it wrong.
Again, thanks for the assistance. Very nice of you to help
Well it looks like the drivers are incorporated into the output transistors as they as a 'Darlington' type device.
https://en.wikipedia.org/wiki/Darlington_transistor
The hot output transistors are hot because they are passing more current than they should (because the bias is to high). The test points on CN715 measure the voltage across the parallel 0.47 ohm resistors and if that is where you are measuring your 114mv then you have nearly half an amp flowing (500ma) when it should be nearer 33ma. So that is why they are hot.
Other reasons causing that can be oscillation and instability but you would need an oscilloscope to look for problems like that.
If you short out (put a link across) C7125 you remove the bias completely and the amp should run cold with zero bias. It will still work as a an amp though and still play.
https://en.wikipedia.org/wiki/Darlington_transistor
The hot output transistors are hot because they are passing more current than they should (because the bias is to high). The test points on CN715 measure the voltage across the parallel 0.47 ohm resistors and if that is where you are measuring your 114mv then you have nearly half an amp flowing (500ma) when it should be nearer 33ma. So that is why they are hot.
Other reasons causing that can be oscillation and instability but you would need an oscilloscope to look for problems like that.
If you short out (put a link across) C7125 you remove the bias completely and the amp should run cold with zero bias. It will still work as a an amp though and still play.
It's a possibility that we have gone on too many topics at the same time.
The hot transistors are the center, front left and, surround left oddly enough, Not the Surround Right. Currently, they are all running around 54-57°C. Amp still idle.
The hotter chips I saw earlier was the center, front left and surround left. All of those measure at 8mV ± .3, I have checked them at least 3 different times.
The only transistor 'set' running out-of-range is the front right which is being repaired tomorrow.
I'm measuring it as specified on page 201.
Did I read that right though? Shorting C7125 (capacitor) will have it running without bias? Isn't that something I should look at after I get the parts in?
The hot transistors are the center, front left and, surround left oddly enough, Not the Surround Right. Currently, they are all running around 54-57°C. Amp still idle.
The hotter chips I saw earlier was the center, front left and surround left. All of those measure at 8mV ± .3, I have checked them at least 3 different times.
The only transistor 'set' running out-of-range is the front right which is being repaired tomorrow.
I'm measuring it as specified on page 201.
Did I read that right though? Shorting C7125 (capacitor) will have it running without bias? Isn't that something I should look at after I get the parts in?
I thought you were meaning the output transistors were hot and that the 114mv was the lowest bias setting you could achieve.
Many of the IC's and transistors and voltage regulators in something this complex will run hot, that's normal. The output transistors on each power amplifier stage should not be hot though.
Many of the IC's and transistors and voltage regulators in something this complex will run hot, that's normal. The output transistors on each power amplifier stage should not be hot though.
Yes, that will force zero bias current in an otherwise correctly working output stage.
100mV is the lowest and 114 mV is the highest. I made sure I could adjust it based on an earlier post. This is just with the front right channel.
Just for reference, can you give me a schematic location of the output transistor? Want to understand this fully.
Again, I thank you for keeping up with this thread. Glad I found this forum!
Just for reference, can you give me a schematic location of the output transistor? Want to understand this fully.
Again, I thank you for keeping up with this thread. Glad I found this forum!
These are the output transistors, there is a pair per channel.
The bias current is measured by looking at the voltage between CN725 pins 1 and 3 and calculating it using ohms law. 8 mv would be 34ma current which sounds a reasonable value. You do that for each channel.
The bias current is measured by looking at the voltage between CN725 pins 1 and 3 and calculating it using ohms law. 8 mv would be 34ma current which sounds a reasonable value. You do that for each channel.
What would a normal temperature be on these output transistors, in Celsius? The bias transistor on the bad channel is running quite hot at somewhere around 90c. (Still nothing running).
Should I just shut it down till FedEx comes?
Should I just shut it down till FedEx comes?
Post a screenshot of the diagram and circle the transistor that is getting hot. 90C does sound excessive for any component in a domestic product like this. The bias transistor should run cold of itself.
The screw for Q7225 is 90°C, the temperature where the transistor meets the heatsync is around 100.
When I am in there today, I'm going to wipe all the thermal paste off and put new on. I have Artic Ceramique and that was what was on it when I started. I know through years of computer experience that should have been wiped down the first time I took it off.
Obviously it's not making a good solid contact. Because a few of them are a little warm as well, and there are no issues with their pathway/stage/channel.
When I am in there today, I'm going to wipe all the thermal paste off and put new on. I have Artic Ceramique and that was what was on it when I started. I know through years of computer experience that should have been wiped down the first time I took it off.
Obviously it's not making a good solid contact. Because a few of them are a little warm as well, and there are no issues with their pathway/stage/channel.
Q7225 should have only a low voltage across it from C to E and it passes only a low current. I would think the transistor is hot because the heatsink is hot and that is because the output transistors are passing to much current.
C to E was one of the reasons I decided to change this transistor. It was way out of range of the other bias transistors.
I'm about ready to dive into it, I'll let you know how far out of range it is in a little bit. However, I seem to remember double of what it's supposed to be.
I'm about ready to dive into it, I'll let you know how far out of range it is in a little bit. However, I seem to remember double of what it's supposed to be.
Kinda figured most stuff needs to be tested out of circuit but the this was the only transistor that ran over. The rest of the 8 channels matched or nearly matched.
So you need to make sure.
A problem with the diodes and/or Zener diodes across it and/or problems with the output transistors can all effect the reading in circuit.
The removed or isolated transistor should read open circuit from C to E with the red meter lead on the collector.
A problem with the diodes and/or Zener diodes across it and/or problems with the output transistors can all effect the reading in circuit.
The removed or isolated transistor should read open circuit from C to E with the red meter lead on the collector.