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Pioneer Spec-1 low output on left channel

A

Adeyfk

New Member
Hi, I have a Spec-1 and the left channel is low. I've been looking at the schematics for the amp and just can't seem to locate some good interim probe points to connect my Oscilloscope to to try and isolate the location of the issue.
It seems to me that there is a transistor that has failed or gone out of spec, but I can't Isolate it to the Equalizer, buffer, filter or tone amplifier circuit.

Any help so that I can narrow it down would be appreciated.
 
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Could just be a dirty switch or control potentiometer.
 
Does the problem also exist on AUX and TUNER, use CDP or IPOD/IPHONE,,,
If so, can eliminate phono stage.
 
Some test points

Tone amp AWG-035
Pin 1 (L)
Pin 22(R)
Pin 10(L)
Pin 13(R)

Filter amp AWM-082
Pin 31(L)
Pin 32(R)
Pin 22(L)
Pin 20(R)
Pin 14(L)
Pin 16(R)

upload_2019-8-10_16-29-40.png
 
I have cleaned all pots etc with Deoxit and the problem still exists. The issue is common to the left channel and is not input specific.

Thanks MBZ, that's just what I was looking for. I'll give it a test tonight and see what I can find.
 
The Spec 1 is a preamp. Wiggle the tape monitor and and dubbing switches. Have you swapped the cables to the amp to rule it out?
 
You can run an input using a CD player (Sig Gen makes it easier). Using a DMM set to AC mV's, follow the jumping meter (Jumping to the beat of the music), comparing the strength of the weak channel's signal to the good channel.
Try to probe the input of each board and then the board output.
There is a protection relay. Check both sides if it?
The Spec one is loaded with the 2SA726's which are notorious for failure.
I've been through many of the Spec 1's and all needed to be rebuilt, bringing them back to a reliable standard. There's a lot going on in that pre.
 
zebulon1 said:
You can run an input using a CD player (Sig Gen makes it easier). Using a DMM set to AC mV's, follow the jumping meter (Jumping to the beat of the music), comparing the strength of the weak channel's signal to the good channel.
Try to probe the input of each board and then the board output.
There is a protection relay. Check both sides if it?
The Spec one is loaded with the 2SA726's which are notorious for failure.
I've been through many of the Spec 1's and all needed to be rebuilt, bringing them back to a reliable standard. There's a lot going on in that pre.
Click to expand...
What is the best replacment for the 2SA726's? I am having the same issue. And its not related to any inputs, cable, devices, etc... its containd to the SPEC-1. I will clean all pots again and see it that fixes it. othere then that I dont know where to start.
 
BTW there is a Pioneer section which is the best place for Pioneer gear service input as not everyone visits this section for Pioneer help
I thought most were using KSA992F but I think a KSA1015Y would work just as well, as it has a 100mA max Ic same as 2sa726.
When it comes to switches in the signal path, you can test these signal paths going through the switch contacts using the ohmmeter, with power off of course
or if you have a SG and a scope you can do it that way as well but it wont tell you the contact resistances of the switch which can reveal poor or oxidized contacts.
 
So I have tracked it down, now what to do?

Here are a couple pictures. signal going in Aux1, Aux2, Tape, etc., all the same, that's not the issue. Signal coming out of the Output 1 or 2 both low on the Right channel. I dint know if there are any VR's that can correct this? Front Balance has to be on 2 o’clock to be balanced.

FYI, I cleaned all switches very good.

Other then that the only VR's I can see are on the power supply and I don't see any info on how to set them?

If any one has some ideas on where to start and what to look at I would appreciate it very much.
 

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Suggest moving this to the pioneer forum, gurus there will sort it out pronto, they have a deep understanding of SPEC gear. Hit the REPORT link at the bottom of a post and add text requesting move.
EDIT: Pick a point in the audio path halfway between input and output and probe there, signals balanced, move back/forward accordingly.
On the Tone assy AWG-035 Pin 1(L) and 22(R) are inputs while Pin 10(L) and 13(R)
are outputs on this board.
 
Last edited:
mbz said:
Suggest moving this to the pioneer forum, gurus there will sort it out pronto, they have a deep understanding of SPEC gear. Hit the REPORT link at the bottom of a post and add text requesting move.
EDIT: Pick a point in the audio path halfway between input and output and probe there, signals balanced, move back/forward accordingly.
On the Tone assy AWG-035 Pin 1(L) and 22(R) are inputs while Pin 10(L) and 13(R)
are outputs on this board.
Click to expand...
Moved: SPEC-1, Lower output on the right channel | Audiokarma Home Audio Stereo Discussion Forums
 
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