You need to recognize that a 4 ohm load is a very heavy load and likely to further damage an amp that isn't already working properly. A short is even more difficult--- something has to fail, and it won't be the short. This amp does not feature any short-circuit protection other than fuses
Thank you ...... 4 ohms is more for the amplifier, which is amplifying the sound, not ..... silence.... please Read carefully...please.
I have repaired and built amplifiers for over thirty years
But now I feel like I don't know anything. Experiences don't help. This shows that understanding how a circuit and a device works is not just about changing a part and it will be fixed. Especially if the circuit has a closed control loop.
Thank you ...... 4 ohms is more for the amplifier, which is amplifying the sound, not ..... silence.... please Read carefully...please.
I have repaired and built amplifiers for over thirty years
But now I feel like I don't know anything. Experiences don't help. This shows that understanding how a circuit and a device works is not just about changing a part and it will be fixed. Especially if the circuit has a closed control loop.
I still think that sounds like instability. If you have zero offset then adding a load across that output should not alter the DC conditions.
If you use a DBT it should save the transistor from frying.
No need to replace resistors if they measure correctly.
Please, friends, comment. Why did the Sony designer put the 411 transistor in the circuit in an unusual way? Have you seen such a case?How does the DC voltage drop on the emitter-base transistor 411 not follow the behavior of semiconductors?
Diagrams from service manuals often have errors and mistakes on them. You would expect the base of VT411 to be around -1.8 volts give or take. So it looks like an error.
The collector of the bias control transistor should be on +1.2, but if the emitter is on -1.8, this circuit will be equivalent to having 5 silicon diodes.We simulated the circuit using the software. The result of measuring the voltage between C ... and ..E. in the bias transistor was 2.25 equal to 3 silicon diodes and the PNP power transistors were off.
The bias spreader is a temperature sensitive shunt regulator, analogous to a TL431, but using Vbe as its "Vref reference." The figure is taken from TI's data sheet. I'll assume Vbe=0.6V
To apply this formulation to analyzing our spreader, assume Iref is 0 for simplicity. Maximum spreader voltage is when R1= 5.6k + 1k, and R2=1.2k. This yields Vka= 6.5*Vbe= ~3.9V
Similarly, the minimum spreader voltage is when R1= 5.6k, and R2=1k+1.2k. This yields Vka= 3.55*Vbe= ~2.13V. So it appears that the spreader can be adjusted to appropriate base drive voltages, i.e. about 5*Vbe.
I can only guess why Sony elected three stages of emitter follower to the negative rail, but only two stages to the positive rail. In any case, it must be a viable design. Citizens's conjecture seems reasonable and I think he nailed a good description in post 5. Clearly, the schematic has a few errors.
To apply this formulation to analyzing our spreader, assume Iref is 0 for simplicity. Maximum spreader voltage is when R1= 5.6k + 1k, and R2=1.2k. This yields Vka= 6.5*Vbe= ~3.9V
Similarly, the minimum spreader voltage is when R1= 5.6k, and R2=1k+1.2k. This yields Vka= 3.55*Vbe= ~2.13V. So it appears that the spreader can be adjusted to appropriate base drive voltages, i.e. about 5*Vbe.
I can only guess why Sony elected three stages of emitter follower to the negative rail, but only two stages to the positive rail. In any case, it must be a viable design. Citizens's conjecture seems reasonable and I think he nailed a good description in post 5. Clearly, the schematic has a few errors.
What error are you talking about? I can see the reality of the device. It matches what Sony has published.
Thank you.....the other channel does not destroy the output transistors..... the output transistors are off. But we have sound. for repair , we have to go back to the basics of ss amp . The Simulit software says without vt 411 the circuit is correct. all voltage is good!!!?
I’m sorry, but the image in post 33 is too fuzzy to read.
In the actual working channel, I estimate the observed voltages should be:
output ~0V
VT406 emitter -0.6V
VT411 emitter -1.2V
VT411 base -1.8V
The -1.8V is contrary to what is noted in Sony drawing and which I believe is an error.
Similiar voltages should appear in the problem channel, but there’s a defect not yet found.
In the actual working channel, I estimate the observed voltages should be:
output ~0V
VT406 emitter -0.6V
VT411 emitter -1.2V
VT411 base -1.8V
The -1.8V is contrary to what is noted in Sony drawing and which I believe is an error.
Similiar voltages should appear in the problem channel, but there’s a defect not yet found.
See #27 and #5: it is 1.7 because VT411 is running on low current (Vbe ~ 0.5V).
- fuse can not help for protect power transistors .
-Have you ever seen a amp circuit with more driver transistors on one side?like vt411..?npn=3....pnp=4
-in ab class out put powers should on .so need .5v or .6 v in b ?
- why dc voltag in c of vt403 .... chang when 4.7 ohm lode... conect to output(no sound) (no sound)? owner when use low ohm speaker after som times burnt fuse .he listen with
low voulum .
- can remove vt411?
Use a DBT instead.
#5, #27
Yes.
#13, #15
No, better not do that - this is part of the design.
Yes, you can remove it, but the circuit will behave very different, can become unstable, self destructable even.
Not unusual, have seen this so many times. When it's production time, profits are needed, not discussions.
General advice: bend all the caps away from heat sources. (C310)
Hi hooman,
I've attached a copy of the service manual, which is drawn differently than yours. Yours has a more elegantly drafted positioning of VT411, though the noted voltage is the same. And yours isn't immune from errors, as there is a short drawn across CB2 near the output. There's a interesting variety of drawings available across the web.
In my attached drawing, note how VT411 is "wedged" into the schematic in an ugly manner. I suspect the design may have been modified to add that transistor and that the voltage notation was never updated to reflect its addition.
No, I've never encountered a design that has dissimilar numbers of drivers. I don't admire the design, but it must work and I advise against removing VT411 from the circuit. There must be a reason for its addition, since Sony accepted the added cost of the part. And 5*Vbe spread across the outputs is consistent with the resistor values in the bias spreader. The working channel is proof that the design is workable.
I suggest tabulating voltages side by side for comparison, eg:
Collector Q303 +1.25V Collector Q403 ?
Base Q305 +1.2V Collector Q405 ?
Base Q307 ? +0.6V Base 407 ?
Output ~0V Output ?
Base Q308 -0.6V Base Q408 ?
Base Q306 -1.2V Base Q406 ?
Base Q311 ?-!.7V Base Q411 ?
Emitter Q304 ? Emitter Q404 ?
I suggest measuring with no load attached.
An interesting experiment would be to connect a 10K resistor from output(s) to +35V rail, or -35V rail. This load should be light enough to avoid damage. There should be no effect in the working channel, but there may be interesting suspeptabilty in the problem channel.
BTW, check the voltage at the junction of R406 and R407. It should be mid supply, about -17V.
In the editor, I had the test points and results nicely tabulated. But when I save, all the spacing is deleted. GRRRR!
I've attached a copy of the service manual, which is drawn differently than yours. Yours has a more elegantly drafted positioning of VT411, though the noted voltage is the same. And yours isn't immune from errors, as there is a short drawn across CB2 near the output. There's a interesting variety of drawings available across the web.
In my attached drawing, note how VT411 is "wedged" into the schematic in an ugly manner. I suspect the design may have been modified to add that transistor and that the voltage notation was never updated to reflect its addition.
No, I've never encountered a design that has dissimilar numbers of drivers. I don't admire the design, but it must work and I advise against removing VT411 from the circuit. There must be a reason for its addition, since Sony accepted the added cost of the part. And 5*Vbe spread across the outputs is consistent with the resistor values in the bias spreader. The working channel is proof that the design is workable.
I suggest tabulating voltages side by side for comparison, eg:
Collector Q303 +1.25V Collector Q403 ?
Base Q305 +1.2V Collector Q405 ?
Base Q307 ? +0.6V Base 407 ?
Output ~0V Output ?
Base Q308 -0.6V Base Q408 ?
Base Q306 -1.2V Base Q406 ?
Base Q311 ?-!.7V Base Q411 ?
Emitter Q304 ? Emitter Q404 ?
I suggest measuring with no load attached.
An interesting experiment would be to connect a 10K resistor from output(s) to +35V rail, or -35V rail. This load should be light enough to avoid damage. There should be no effect in the working channel, but there may be interesting suspeptabilty in the problem channel.
BTW, check the voltage at the junction of R406 and R407. It should be mid supply, about -17V.
In the editor, I had the test points and results nicely tabulated. But when I save, all the spacing is deleted. GRRRR!
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