Pioneer Spec 4 outputs

[mrmodify]

Hi all,
I am working on a Pioneer Spec 4 amplifier.
I think I have it repaired but I have not installed the 4 output transistors as of yet.
My question is can I power the unit up with the output transistors removed?

 

[Martaine2005]

Most of the time, it’s not necessary to power it up.
If a short was present with the transistors in and no short with them removed, it’s fairly safe to replace them and power it up.
I always use current limiting bulb (dim bulb tester) to double check on first power up.

 

[mrmodify]

Thanks Martainr
I had several burnt, shorted and open components. I replaced all those and checked the rest of the components on the board with testers.
I am using a DBT and have the outputs removed.
Currently I have 2 transistor on the negative power side of the board that will get hot after about 20 seconds after powering up. I am not sure if I have a problem or if its because of the missing outputs. The positive side does not heat up.

 

[Martaine2005]

Very difficult to say without seeing the circuit.
Are the required voltages present?

 

[Delta Prime]

My question is can I power the unit up with the output transistors removed?

No, you will cause more damage.

I am using a DBT and have the outputs removed

Why would you do that?

I am not sure if I have a problem or if its because of the missing outputs. The positive side does not heat up.

All the above…
Here you go, buddy!
Enjoy.
By the way, have you seen this?

 

[mrmodify]

Very difficult to say without seeing the circuit.
Are the required voltages present?

Very difficult to say without seeing the circuit.
Are the required voltages present?

This is what I came up with. The right channel operates fine. These voltages are in red. The left channel is the one I am working on. The outputs are removed and Q9 & Q11 will get warm after about 15 seconds.


[Mod edit: image rotated and cropped for better readability]

 

[WHONOES]

Can you show us a complete circuit of the power amplifier section including the output transistors and rotate it 90 degrees?

 

[mrmodify]

Yes sir, let me know if this is not good.
Thanks

 

[WHONOES]

Disconnect the output transistors and then measure the output voltage with respect to 0V.

 

[mrmodify]

Disconnect the output transistors and then measure the output voltage with respect

Hi all,
I am working on a Pioneer Spec 4 amplifier.
I think I have it repaired but I have not installed the 4 output transistors as of yet.
My question is can I power the unit up with the output transistors removed?

Update,
Thank all of you for the help. I did power the unit up on a DBT and everything was fine except for the voltage on Q11 & Q10 emitter.
Installed the outputs and powered up again and all voltages were fine. Q11 went from -4vdc to -.6 vdc. Q10 went from 4vdc to .6vdc.
Took amp off of the DBT and powered up on line voltage and again unit operated fine.
Again thanks for the input you guys gave me!

 

[Harald Kapp]

I beg your pardon if the question sounds stupid: What is a DBT?

 

[Martaine2005]

I beg your pardon if the question sounds stupid: What is a DBT?

Dim bulb tester, aka current limiter.

 

[mrmodify]

I beg your pardon if the question sounds stupid: What is a DBT?

No such thing as a stupid question in my mind.
DBT is a dim bulb tester.
It is nothing but a incandescent bulb wired in series with the equipment being tested. It limits the current depending on the size of the bulb. A
100 watt bulb on 120vac will only allow 1.2 amps of electricity for the connected equipment.
If you have a shorted component it keeps from letting the smoke out.

 

[Delta Prime]

It is nothing but a incandescent bulb wired in series with the equipment being tested.

 

[Harald Kapp]

Dim bulb tester, aka current limiter.

Thanks. I know the technique, only the abbreviation was new to me. You never stop learning

 

[mrmodify]

Thanks. I know the technique, only the abbreviation was new to me. You never stop learning

Yes sir, I think there is something that can be learned everyday if I pay attention.

Thanks. I know the technique, only the abbreviation was new to me. You never stop learning