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Help me fix Yamaha R-S700
- Thread starter zepplock
- Start date
OK good. Solderdude is right in that the driver transistors, emitter resistors and fusible resistors need to be checked as well.
Unsolder if required and check(according to the schematic):
Q119C
Q119A
R146
R148
R149
R150
R151
R156 (emitter resister with 2 resistors in one package.)
R159 (emitter resister with 2 resistors in one package.)
You may need to unsolder these resistors & transistors to get a proper measurement with your meter. The resistors can go open or change value.
That's a good start for awhile; if I think of anything else I will update you.
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You will need to wire up a light bulb in series to an outlet that you plug the amp into. That way, if you plug in an amp that has a short, the bulb comes up and doesn't allow (much) damage to the amp. Without it, you could change the output transistors, plug it, and have them all blow up again because there are faults elsewhere! You cannot do an amp repair without this (or a variac with amp meter). There are a lot of videos on it online. Here is an example:
Note that if the amp is very high power with high initial surge current, the bulb may not allow it to power up. But don't worry about that for now and build the fixture before you damage a bunch of parts.
Note that if the amp is very high power with high initial surge current, the bulb may not allow it to power up. But don't worry about that for now and build the fixture before you damage a bunch of parts.
@amirm has a very good point is making the current limiting light bulb circuit for the first power ON of the amp.
It is best if you can make this circuit and use it when powering ON the amp for the first time(and maybe more).
As per testing the transistors.
Use page 56 of the service manual to physically identify the lead layout of the transistors and then you will know the base, collector and emitter layout.
Use these videos to familiarize yourself with transistor testing.
It's important that you check the driver transistors for forward and reverse bias and collector-emitter too which should be open. (out of circuit)
If there are any incorrect readings forward or reverse biased then those transistors will require replacing.
Note: The base-collector meter reading should have a slightly lower meter reading than base-emitter. Collector-emitter should be open.
It is best if you can make this circuit and use it when powering ON the amp for the first time(and maybe more).
As per testing the transistors.
Use page 56 of the service manual to physically identify the lead layout of the transistors and then you will know the base, collector and emitter layout.
Use these videos to familiarize yourself with transistor testing.
It's important that you check the driver transistors for forward and reverse bias and collector-emitter too which should be open. (out of circuit)
If there are any incorrect readings forward or reverse biased then those transistors will require replacing.
Note: The base-collector meter reading should have a slightly lower meter reading than base-emitter. Collector-emitter should be open.
OP
zepplock
Active Member
- Thread Starter
- #26
Yay, good news. I got 4 transistors in question out (from 1 side, left channel). Tested them, 3 are bad (I guess I missed one when I said all 4 were bad).
The unit actually powers up, I have all switched working (pure direct, A, B speakers, etc), LED display is on, radio, etc. I didn't connect my main speakers, obviously. I also tested additional resistors (without soldering those out) and the ones with values in manual tested ok.
I guess next step is to get 4 new transistors for left channel.
The unit actually powers up, I have all switched working (pure direct, A, B speakers, etc), LED display is on, radio, etc. I didn't connect my main speakers, obviously. I also tested additional resistors (without soldering those out) and the ones with values in manual tested ok.
I guess next step is to get 4 new transistors for left channel.
Welcome back You've been busy with this repair.
I know you tested the driver transistors(I think you did) Q119C and Q119A and that was to see if there was a obvious cascade failure but we are going to replace those too just for the heck of it.
This is common practice, some do and some don't but in your case because we are doing this repair remotely via chat I think it best if we replace those too.
So replace the 4 output transistors and the 2 driver transistors for a total of 6 transistors
Keep in mind that this is a very complex device and that it's difficult to ensure everything is done near perfectly and there might be further issue down the road and the light bulb circuit will help to prevent a blow out when powering it up the first time if there is anything else that is bad.
Did you build a light bulb current limiter circuit?
Now that you are pretty familiar with the unit did you see anything that appeared to be running hot, has a brown heat mark on the circuit board or resisters/transistors that appear to have been hot?
You've been busy with this repair.I know you tested the driver transistors(I think you did) Q119C and Q119A and that was to see if there was a obvious cascade failure but we are going to replace those too just for the heck of it.
This is common practice, some do and some don't but in your case because we are doing this repair remotely via chat I think it best if we replace those too.
So replace the 4 output transistors and the 2 driver transistors for a total of 6 transistors
Keep in mind that this is a very complex device and that it's difficult to ensure everything is done near perfectly and there might be further issue down the road and the light bulb circuit will help to prevent a blow out when powering it up the first time if there is anything else that is bad.
Did you build a light bulb current limiter circuit?
Now that you are pretty familiar with the unit did you see anything that appeared to be running hot, has a brown heat mark on the circuit board or resisters/transistors that appear to have been hot?
While your parts/transistors are being shipped that is a good time to familiarize yourself with the calibration procedure that will be required after you confirm the amp is working in good order.
Do this procedure before connecting the speakers:
Page 32 of 84 in the service manual will indicate how to check and adjust the Idling current. This needs to be checked and adjusted if required.
Do this procedure before connecting the speakers:
Page 32 of 84 in the service manual will indicate how to check and adjust the Idling current. This needs to be checked and adjusted if required.
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Cahudson42
Major Contributor
- Joined
- Sep 21, 2019
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@Doodski :
Does this Yamaha use the 'clipped resistor' idle current adjustment? Or a pot?
If 'clipped resistor', perhaps this is a great time for one of our hardware experts (you
) to develope an adjustable series fixed + pot replacement for the 'clipped' resistor? And the procedure to adjust it? That way both channels can be precisely balanced, and the usual under-biased setting corrected so as to reduce crossover distortion?
Yes, it uses the clipped resistor method.@Doodski :
Does this Yamaha use the 'clipped resistor' idle current adjustment? Or a pot?
If 'clipped resistor', perhaps this is a great time for one of our hardware experts (you
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solderdude
Grand Contributor
After checking the resistors there is a little check you can do to see if the other components are still O.K. before you solder in the new power transistors and possibly driver transistors.
What you can do as a test (NO speakers connected) is to take a 100 Ohm resistor and put it in place between the B and E connection pad of the removed power transistor. This should be the outer connection pads. Ensure the middle pad is not connected by accident. ONLY on one of the NPN transistors so 121C or 123C.
Then solder a second 100 Ohm resistor between the B and E pad of 121A or 123A as well.
When you power on the amp the output DC voltage should be around 0 Vdc, could be off several mV.
Then you measure the voltage across D107. This should be around 2.2V DC.
Next measure the voltage across R 147 which should be somewhat above 1V (between 1 and 1.2 or so)
When this all pans out you can pretty safely solder in the power transistors.
Follow the procedure in the manual as there is no pot (which is a good thing in some cases).
If the quoted values are not reached you need to adjust the bias and the clipped resistor must be replaced with a value determined by a trimmer pot that is temporarily fixed in place of the clipped resistor. This is a dangerous thing. adjust the value too low and you can blow the output stage again so in such case would recommend to use a trimmer pot with a resistor in series of at least 680 Ohm in series with it.
As doodski mentioned, even when the driver transistors 119A and 119C measured O.K. it may be best to replace them as well. They might have suffered some latent damage (damage that leads to failure after some time) just to be sure.
What you can do as a test (NO speakers connected) is to take a 100 Ohm resistor and put it in place between the B and E connection pad of the removed power transistor. This should be the outer connection pads. Ensure the middle pad is not connected by accident. ONLY on one of the NPN transistors so 121C or 123C.
Then solder a second 100 Ohm resistor between the B and E pad of 121A or 123A as well.
When you power on the amp the output DC voltage should be around 0 Vdc, could be off several mV.
Then you measure the voltage across D107. This should be around 2.2V DC.
Next measure the voltage across R 147 which should be somewhat above 1V (between 1 and 1.2 or so)
When this all pans out you can pretty safely solder in the power transistors.
Follow the procedure in the manual as there is no pot (which is a good thing in some cases).
If the quoted values are not reached you need to adjust the bias and the clipped resistor must be replaced with a value determined by a trimmer pot that is temporarily fixed in place of the clipped resistor. This is a dangerous thing. adjust the value too low and you can blow the output stage again so in such case would recommend to use a trimmer pot with a resistor in series of at least 680 Ohm in series with it.
As doodski mentioned, even when the driver transistors 119A and 119C measured O.K. it may be best to replace them as well. They might have suffered some latent damage (damage that leads to failure after some time) just to be sure.
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OP
zepplock
Active Member
- Thread Starter
- #32
Ok, so I came back from vacation and finally had time to work on it.
I soldered transistors back and checked DC voltages where service manual suggested (just 2 of those big white 3-leg resistors). There was no channel imbalance.
But I could not do 2 things:
- have a lightbulb thing since I could not find any incandescent bulbs in my house, go figure. Has to be incandescent, right? So I skipped it since I knew unit powers up without one channel after I unsoldered broken transistors.
- could not reliably check DC voltage across speaker terminals. It was jumping between zero and fraction of mv. I think my multimeter is flaky at low voltages.
- Kept old Q119C and Q119A in place since they tested ok and in order to unsolder them I need to remove the whole heatsink with sensors, etc.
I ran an amp for some time to make sure it does not heat up, both heatsinks stayed a bit warm with.
Overall I'm happy with sound and functionality, even though I skipped on some suggestions. I definitely need better soldering iron, better multimeter and some other tools if I decide to do it again!
Tnanks guys/gals, you are amazing!
I soldered transistors back and checked DC voltages where service manual suggested (just 2 of those big white 3-leg resistors). There was no channel imbalance.
But I could not do 2 things:
- have a lightbulb thing since I could not find any incandescent bulbs in my house, go figure. Has to be incandescent, right? So I skipped it since I knew unit powers up without one channel after I unsoldered broken transistors.
- could not reliably check DC voltage across speaker terminals. It was jumping between zero and fraction of mv. I think my multimeter is flaky at low voltages.
- Kept old Q119C and Q119A in place since they tested ok and in order to unsolder them I need to remove the whole heatsink with sensors, etc.
I ran an amp for some time to make sure it does not heat up, both heatsinks stayed a bit warm with.
Overall I'm happy with sound and functionality, even though I skipped on some suggestions. I definitely need better soldering iron, better multimeter and some other tools if I decide to do it again!
Tnanks guys/gals, you are amazing!
Well done! Tools for electronics repair are specialized and can add up $ pretty fast. Glad to hear your amp worked out
I appreciate the YouTube video demo. The sound is very trebly'ishy. I am guessing that is what you are commenting on. Have you tried adjusting the loudness and bass features to get more bass and more warmth.
ZolaIII
Major Contributor
- Joined
- Jul 28, 2019
- Messages
- 4,160
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Had a bad network power (low voltage) after hard wind last night and my R-N402D went into power protection blocking mode (blinking led when power button pressed not coming on). To rest the power protection block on this unit you need to press and hold the < preset and +bass buttons and then press power. It will unblock it and went to self testing mode.
Luckily for me it all went good, I wanted to share this if anyone gets in similar position with this unit.
Best regards and have a nice time, hope this will help someone else also.
Luckily for me it all went good, I wanted to share this if anyone gets in similar position with this unit.
Best regards and have a nice time, hope this will help someone else also.
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