Another sx-1010 Resto

[markthefixer]

you have proceeded correctly.

be sure you can adjust the offsets, then we know the readings are valid. IF you adjusted them to those values, let me know and proceed.

check the power supply voltages, both the big main caps and regulated voltages on awr-054 pins 6-15 against a bare metal chassis ground. IF any of the non-grounded pins show zero volts check the last resistor connected in series in the foil to the pin.(R11,12,13,14,15,20,21)

Then measure the base voltages going to each of the empty output transistor pairs. You should see 0.6v positive to the npn outputs (pin 10) and -0.6v to the pnp outputs (pin 13) referenced to chassis ground...

 

[craxx6969]

The readings at the audio output came without me adjusting vr1. The readings were there after I zeroed at vr1. When I do turn the vr1 screw either way there is no change in the output voltage.

Waiting for further instructions. I am out of the state today and will return on WED.


Thanks

you have proceeded correctly.

be sure you can adjust the offsets, then we know the readings are valid. IF you adjusted them to those values, let me know and proceed.

check the power supply voltages, both the big main caps and regulated voltages on awr-054 pins 6-15 against a bare metal chassis ground. IF any of the non-grounded pins show zero volts check the last resistor connected in series in the foil to the pin.(R11,12,13,14,15,20,21)

Then measure the base voltages going to each of the empty output transistor pairs. You should see 0.6v positive to the npn outputs (pin 10) and -0.6v to the pnp outputs (pin 13) referenced to chassis ground...

 

[markthefixer]

sigh, that's not good.

 

[craxx6969]

I am back in town and wait to find out what the next step is in this mess.

sigh, that's not good.

 

[markthefixer]

The easiest explanation is that the output you measured isn't connected to the feedback point.

The output HAS to be adjustable by the offset.

What are the voltage measurements of pins 10 and 13 to ground?

 

[craxx6969]

As requested here are the voltage readings of pins 10 and 13 to ground:

Right Board
Pin 10 = -45.2v
Pin 13 = -53.9v

Left Board
Pin 10 = 397.6mv
Pin 13 = -373.3mv

Per the schematic Pin 10 and 13 show 0.6v from the emitters of Q9 and Q10

Wait...

thanks
JT

The easiest explanation is that the output you measured isn't connected to the feedback point.

The output HAS to be adjustable by the offset.

What are the voltage measurements of pins 10 and 13 to ground?

 

[markthefixer]

well, I think you see: the right channel board has a serious problem.

let's concentrate on being sure the left channel is working.

On the left board, slowly and carefully increase the idle current setting and watch those pin 10 and pin 13 voltages increase.

Then see if they can be shifted a few tens of millivolts using the offset adjustment.

 

[craxx6969]

Yes, I saw that as soon as I took the readings from Pins 10 & 13. Wonder why the magic smoke didn't appear...

Left board,
increased idle current setting while watching voltage on the 10 & 13 pins. Voltage did go up while increasing idle.
Using offset (vr1) I was able to increase and decrease the voltage reading from pins 10 & 13.

So it appears the left board is working according to the test.

Waiting for next step on the right board..
thanks,

JT

well, I think you see: the right channel board has a serious problem.

let's concentrate on being sure the left channel is working.

On the left board, slowly and carefully increase the idle current setting and watch those pin 10 and pin 13 voltages increase.

Then see if they can be shifted a few tens of millivolts using the offset adjustment.

 

[craxx6969]

UPDATE!!!
I just rechecked all my soldering on the right board... DANG, I found one pad that was not solder, just kick my rear.. So I soldered the pad and rechecked my voltage readings on pins 10 & 13.

Pin 10 = not stable, range from -0.028 to 0.159 it does not stabilize
Pin 13 = -0.366v stable

AND I have a relay clicking in...

Adjusting idle did increase the voltage on pin 10 but it is still unstable. I did not try to use vr1 (offset) when checking pin 10.

I adjusted the idle carefully and watched pin 13 voltage... rise it did and using vr1 was able to move the voltage up/down. So due to one pad not being solder caused this issue... Looks like R21 one leg was not soldered..

I will wait for further instructions.

Thanks,
JT

 

[craxx6969]

UPDATE to the UPDATE

After checking the rest of the solder joints, all were good on the board so I then checked the solder joints on the resistors that I have installed on pins 10 to 19 and 13 to 19. The lead on pin 19 was barely on so I resoldered it. I then checked the voltages on pins 10 and 13 on the RIGHT board. Viola, both are stable and when I adjust the idle current ever so slightly the voltages on both 10&13 go up as intended. I then used vr1(offset) to see if adjusting it would raise the voltage and it did raise it.

So why would 13 be stable and not 10 when the lead was barely on? Hmm..

We continue to have a relay click, lights are on (two function bulbs are out but will WAIT for further instructions.

Appears it getting closer..

Thanks,

JT

 

[markthefixer]

If you can control the pins 10 and 13 voltages around +/- 0.6 volts with the idle current and offset settings on BOTH boards, I think you are good to go with reinstalling the power output transistors. :thmbsp:

of course proceed carefully, ohmmeter checking for installation short circuits - get a bare screw into the heat sink that you can clip an ohmmeter wire to for a reliable check.

 

[craxx6969]

Will do on the control issue. I will double check all the readings before I install the output transistors. And I will check the output transistors for possible shorts.

 

[craxx6969]

Well this is a real heartbreak,, I did my final check on the offset and it was dead on at the audio outputs before I installed the output transistors. I've checked them at least three times during this repair and I've just rechecked them again. After install and checking for shorts I have a short somewhere!!! DA!!! what the @#$#$# happened between removing the resistors and installing the outputs. So i checked continuity between the pins and the leads to the outputs, no shorts or opens.. uninstalled the outputs and checked them, ALL are okay. Reinstalled, STILL a bright light on the dbt.. Yes, I wanted to make sure I didn't mess something up after all this work. So I'll take the outputs out, wrap the output connectors, install the resistors on pins 10, 13 to pin 19 to see if there is still a short. I'll report after that.... ... what a let down. time to quit and get some zzzzzz's.

 

[markthefixer]

Do NOT press on when tired. It will be a one step forward, three steps back situation.

 

[craxx6969]

okay, i've removed the output transistors, taped off the output transistors connectors and soldered on the resistors to pins 10 and 13 to pin 19. On the dbt just in case..
Lights up bright and then dims, then relay clicks.. What is the issue? Am I not installing the outputs correctly? Hmm.. this is a real headache... so am I checking the outputs to heatsink correctly? thought i was... something rotten in this...

 

[craxx6969]

Fwiw:

Has anyone put real short shrink tube on the output transistor pins that would protect the bare areas of the output transistor from touching the heatsink?

Just thinking of ways that could fix this issue.

JT

 

[markthefixer]

all four connections on each output transistor have to be isolated, two pins for emitter and base, and the two mounting screws and hardware connected to the collector.
The sockets have a projection that fit into corresponding depressions on the heat sink to align the sockets before tightening, if out of alignment the sockets will be destroyed.

There are two possibilities: either there is a short to ground, or the transistors are doing as told, and conducting heavily inappropriately at the same time causing the apparent short.

Bring it up with the bulb glowing and measure the voltages of the emitter base and collectors of the output transistors.

IF they are out of circuit right now, bring it up and check the raw (big caps) and regulated voltages, as well as the intended output transistor base voltages - checking that the idle and offset adjustments still work.

Another idea is to try doing one channel and see what happens, THEN either add the second channel if the first is ok, or remove the first and add the other.
In other words one at a time to see if the problem is isolated to a specific channel.

 

[craxx6969]

Mark the trans are out of the unit. I'll bring it up on the dbt and measure the main filter caps raw volts and regulated voltage. I'll also check base voltage for the output trans and post
I'll recheck offset and the idle adjustments. Then if necessary do one side at a time leaving the resistors on the side not being replaced with the outputs. All this on raw or DBT?

thanks
JT

 

[craxx6969]

I'll attack it tomorrow night. Zzzz's are in order.

 

[markthefixer]

no dbt if no outputs connected, nor the main caps rewired.