It just keeps blowing...

[keeney123]

Re: It just keeps blowing...

If you look at the service manual, you will see for example, the BASE of Q534 goes out to the Collector of the driver Transistor TR828 another section as shown in PDF schematic 6/13 PDF page 91, if that transistor has bad leakage it will bias on Q534 on hard and will cause the direct couple circuit have bad chain effect, so you should check that transistor and the other two differential pair Transistors. All the amps has the same setup, the driver Transistors are on another section.

It is hard for me to see could you show the leakage path? Please!

[budm]

Re: It just keeps blowing...

If TR828N is stuck fully on or has low resistance between E-C then TR534 and the chain will be turned on hard.
It is very simple amplifier with diff input running on dual supplies.
http://sound.whsites.net/amp_design.htm

[keeney123]

Re: It just keeps blowing...

If TR828N is stuck fully on or has low resistance between E-C then TR534 and the chain will be turned on hard.
It is very simple amplifier with diff input running on dual supplies.

That is not what I am talking about. In order for the E to C to have leakage current there has to be a path from +57 volts to -57 volts. It will have to go through resistors which will be dropping voltage and lower current in the path between these voltages. There is a 47 ohm swamming resistor on the emitter of the transistor.

[budm]

Re: It just keeps blowing...

What do think when audio signal is fed into the amplifier, those transistors will be full conducting or partial conducting (depend on audio level) with the signal, but if one of the device in the chain is stuck on what do you think it is going to happen?
What happen if that TR828 has leakage resistance of lets say 100 Ohms
TR532 (Clooector is connected to + supply) is bias on by R606/608/C542 Bootstraping so you have current flow through R620, E-B junction of TR534 so it is turned and give more current flow through R620 , and through 100 Ohms leakage, and then then through R888 (47) to - supply, at the same time when T534 is on, TR538 will also be on. It does not take much current to burn up that 330 Ohms resistor. At static, the circuit is balanced to give center point output to be at 0V, when thing gets out of balance due to static shorts or leakage then the circuit will get out of balance instead of swinging with the sync with the audio signal.

[keeney123]

Re: It just keeps blowing...

What do think when audio signal is fed into the amplifier, those transistors will be full conducting or partial conducting (depend on audio level) with the signal, but if one of the device in the chain is stuck on what do you think it is going to happen?
What happen if that TR828 has leakage resistance of lets say 100 Ohms
TR532 (Clooector is connected to + supply) is bias on by R606/608/C542 Bootstraping so you have current flow through R620, E-B junction of TR534 so it is turned and give more current flow through R620 , and through 100 Ohms leakage, and then then through R888 (47) to - supply, at the same time when T534 is on, TR538 will also be on. It does not take much current to burn up that 330 Ohms resistor. At static, the circuit is balanced to give center point output to be at 0V, when thing gets out of balance due to static shorts or leakage then the circuit will get out of balance instead of swinging with the sync with the audio signal.

My understanding is he is not putting a signal in it he is just turning it on and it does this. Thank you for the path I will lock at it closer.

[budm]

Re: It just keeps blowing...

If one of the semi is bad then it does not matter if he has signal or not, the circuit will be thrown out of balance when you have bad device in the circuit.

[keeney123]

Re: It just keeps blowing...

What do think when audio signal is fed into the amplifier, those transistors will be full conducting or partial conducting (depend on audio level) with the signal, but if one of the device in the chain is stuck on what do you think it is going to happen?
What happen if that TR828 has leakage resistance of lets say 100 Ohms
TR532 (Clooector is connected to + supply) is bias on by R606/608/C542 Bootstraping so you have current flow through R620, E-B junction of TR534 so it is turned and give more current flow through R620 , and through 100 Ohms leakage, and then then through R888 (47) to - supply, at the same time when T534 is on, TR538 will also be on. It does not take much current to burn up that 330 Ohms resistor. At static, the circuit is balanced to give center point output to be at 0V, when thing gets out of balance due to static shorts or leakage then the circuit will get out of balance instead of swinging with the sync with the audio signal.

Would it not charge through C542 readily and when the two zeners and two diodes get to the correct voltage It would conduct lowering the voltage on C542 so it would charge again? And at some time TR528 will conduct?

[budm]

Re: It just keeps blowing...

TR528 is part of the active Bias circuit for the output section, and it is conducting already to maintain bias.
What do you that what that TR528 is for?
I guess you did not read those links I provided.
More:
http://www.eetimes.com/document.asp?doc_id=1272214

[petehall347]

Re: It just keeps blowing...

here you go this should help anyone learning ....

[keeney123]

Re: It just keeps blowing...

TR528 is part of the active Bias circuit for the output section, and it is conducting already to maintain bias.
What do you that what that TR528 is for?
I guess you did not read those links I provided.
More:
http://www.eetimes.com/document.asp?doc_id=1272214

It is very obvious that it is a bias circuit I already knew that. We are talking about your theory of TR828 leaking, not a normally operating circuit. We now have a 100 ohm transistor with C524 conducting so the bias circuit is a mute point as a pond power up it is getting shorted out by the capacitor. At some time when enough voltage is built up of the cap. for the bias to take effect the resistor bias and zener and diodes conduct. The voltage on the cap will dump and charge so this is a oscillation. I have not tried to figure out the exact voltage when all of this will happen if TR828 is indeed leaking because I would not be able to figure out exactly what resistance it would have.
All I was asking was if you could draw a path for the leakage current which you had suggested and then I asked would not C542 cap be the major path of conduction with the leaky transistor as the power was applied.I will not be working on this amplifier equipment so going into a detailed understanding of every part of every type of amplifier circuits would not be worth it as I would forget that knowledge in a very short time. I find somethings interesting and wanted to explore your theory. I know how these device work, meaning how each component works and understanding how they work together is a matter of study. For me I have a very difficult time at looking at all these crossing lines that do not connect or things that are omitted and the schematic broken in pieces. That is something I was born with. Instead of me trying to go through all that trying to see the leakage path I ask you as you had already saw it. I also thought in the process of you showing me this you would also be showing anyone that was interested in this thread. Also, your links are available for any young technician wishing to learn the operation of these circuits.

[budm]

Re: It just keeps blowing...

When that 100 Ohms is in place then you will have understand how that will affect the bias scheme of all the transistors after that, I do not have the time to explain. All you have to do is to calculate what the Vdrops will be on each components.
C524 conducting, what do mean by that? It is part of the Boostrap circuit, its jobs has nothing to do with DC Voltage when the failed transistor has 100 Ohms is in place of the transistor, it has to do with the impedance of the circuit, that cap can be left out and the circuit will still go out of balance.

bootstrapping principle.

http://www.edaboard.com/thread237660.html

[rievax_60]

Re: It just keeps blowing...

NB = non-burning ( which seems not to be always the case )
R620 - Carbon film 330 ohm 1/4W(NB)
R622,624 - Carbon film 1 ohm 1/4W(NB)


I have not checked any of the resistors with e multimeter... just the transistors. I checked the resistors only visually and cut R620 so that I can close the hood.
When the parts arrive, I will disassemble the boards and test everything.

By the way, could faulty emitter resistors cause this damage?
Now I remember that I got good ohm readings on them and decided not to change them.

There are many possible faults that can be present in the idle current setting circuit that will cause the output stage to be damaged at power on. The idle current setting circuit can be checked independently or use the precaution mentioned in post 7.

[keeney123]

Re: It just keeps blowing...

here you go this should help anyone learning ....

I am very unconventional how I learn. I learn abstractly. It is the easiest way for me to learn. Thank you your time in providing this and I am sure any technicians and future technicians will find this very useful.

[keeney123]

Re: It just keeps blowing...

When that 100 Ohms is in place then you will have understand how that will affect the bias scheme of all the transistors after that, I do not have the time to explain. All you have to do is to calculate what the Vdrops will be on each components.
C524 conducting, what do mean by that? It is part of the Boostrap circuit, its jobs has nothing to do with DC Voltage when the failed transistor has 100 Ohms is in place of the transistor, it has to do with the impedance of the circuit, that cap can be left out and the circuit will still go out of balance.

bootstrapping principle.

http://www.edaboard.com/thread237660.html

As I said I was exploring your idea. C524 conducts on power up with your leaky cap. We are not talking about a different circuit then the one we have. We are only talking about one moment in time when the components fail. I am not asking to explain in detail the circuitry. I don't have the time to figure that all out as there are many things happening at the same time and many things happen in the future time with this leaky transistor circuit. If I had nothing to do I would figure it out. I am sorry I wasted your time. I will not ask you any more questions.

[rievax_60]

Re: It just keeps blowing...

When that 100 Ohms is in place then you will have understand how that will affect the bias scheme of all the transistors after that, I do not have the time to explain. All you have to do is to calculate what the Vdrops will be on each components.
C524 conducting, what do mean by that? It is part of the Boostrap circuit, its jobs has nothing to do with DC Voltage when the failed transistor has 100 Ohms is in place of the transistor, it has to do with the impedance of the circuit, that cap can be left out and the circuit will still go out of balance.

bootstrapping principle.

http://www.edaboard.com/thread237660.html

In post #3 in that link, the diagram and explanation are incorrect. The capacitor needs to connect to the Emitter of Q2.

[budm]

Re: It just keeps blowing...

In post #3 in that link, the diagram and explanation are incorrect. The capacitor needs to connect to the Emitter of Q2.

What capacitor and what Q2?

[rievax_60]

Re: It just keeps blowing...

What capacitor and what Q2?

The capacitor with the reference "C" and the transistor with the reference "Q2" in the diagram in post #3 in this link, http://www.edaboard.com/thread237660.html

[budm]

Re: It just keeps blowing...

Post 9 explain what post 3 is.
This one is better:
https://cdn.badcaps-static.com/pdfs/...8f9437ce2d.pdf

http://www.tedpavlic.com/teaching/osu/

[rievax_60]

Re: It just keeps blowing...

Post 9 explain what post 3 is.
This one is better:
https://cdn.badcaps-static.com/pdfs/...8f9437ce2d.pdf

http://www.tedpavlic.com/teaching/osu/

I had missed post #9. Post #3 is very misleading though.

[keeney123]

Re: It just keeps blowing...

The voltage on the cap will dump and charge so this is a oscillation.


This part of my statement is incorrect. Once the cap charges it will stay charge because of the DC source. With that said I realize to give an accurate analysis of all the detail of this circuitry as BudM I would have to do a detail study. My choice is to do other things that I enjoy like art and helping people what I can. At this time I feel my contribution would do more harm than good so with that I bid BadCaps Forum farewell.