Novice repairing a SX 1080 In Protection Mode

Novice repairing an SX 1080 In Protection Mode *Pictures

As the title states, I am a novice attempting to repair this SX1080. Big mistake already?


I have been searching a lot of the previous threads about the common SX units going into protection mode and thought that I could come to the understanding of my problem by seeing others problems/solutions.


Unfortunately I am unable to really figure out what is going on with my Sx 1080 to determining the issue/s. I am initially thinking it's the Q8 and Q1 replacement on the below boards, but I'm not entirely sure since the readings don't look off to me. Could this be the thermal switch issue as well? I am am totally new to ripping into electronics and was hesitant to do so for fear of making things worse (just like I did when I was 15 my dad passed his 1080 on to me). But since I have seen others with success I figured I'd give it a go.


I have recently purchased this beauty a few months ago and have wanted to recreate the same receiver and speaker setup I had 25 years ago (just like dad gave me.) Fast forward to a few months ago and this newest rig was working fine except for a few pots that needed cleaning, bulbs replacing. I managed up the courage to deox a few things to get it back to sounding good and staying on the selected input. Blue LED's were added for effect.




Fast forward a few more weeks and I decided to refinish the bonnet.










Onto my latest issue....at the initial power up after the bonnet freshen up, the unit was going in and out of protection mode for 5 minutes, then is stayed in protection mode; NO sound. I checked for the usual shorts of speaker wires, fuses, but came up empty handed. It has since not gone out of protection mode and i have began the task of testing the various inputs. I managed to figure out how to take readings with the DMM w/o making anything worse (miracle). I was not sure how to take readings of the PA3004 IC. Do I test each prong? not sure what to do next?















Readings below.

awr-152

pin 22 +60v *+65.2v*
pin 23 +23v *+25.4v*
pin 29 -13v *went back and forth -17v to -35v*
pin 25 -23v *-23.8v*
pin 27 -60v *-64.8v*
pin 16 +13v *+13.93v*
pin 19 +76v *+80.3v*

awm-120

pin 5 0.000v *0.0v*
pin 8 0.000v *0.0v*
pin 2 -60v *-64.6v*
pin 3 21v AC - Wasn't able to make this reading (i believe it's an AC reading per the other threads)
pin 9 +13v *+13.7v*
pin 10 +76v *+80.7v*
pin 4 +12v or so. *12.4v*

Fro the AC part, you have to switch your DMM to AC. see image below



It would also be advisable to wrap the metal prongs of the DMM with heat shrink wrap or insulation from a wire and exposing only the tip to ensure you dont short out anything.

Have you check DC offset ?

So, now it is continuously in protection?

Yes you measure at each pin of the pa3004, and also Q2 (2sc1438)

BUT like qguy said, INSULATE all but the tiniest point of the tip of the probe - a slip will short and destroy things. and... we ** ALL ** slip - when we move our eyes to read the meter. Plain old office type transparent tape works fine.

The tipoff is Q2's base (ecb) and pin 3 of the pa3004 ( there sometimes is no pin 2).
That point is unambiguous, if it is at +0.7v the relay should be ON. If it is at zero (0.000v) the relay should be off.
Q2 could have failed, based on the readings you posted, IF pins 5 and 8 are really 0.000 or at least under 0.1v (positive or negative volts).

pin 29 -13v *went back and forth -17v to -35v*

Click to expand...

pins 9 and 29 are the 7.5v ac circuit for the LEDS, and you should find no dc voltage on them. Luckily they are not used in the protect circuit, the 21v is tapped for that. So don't sweat that reading, no problems are showing so far

There IS a GOTCHA in this circuit, if AWM-120 C1 220uf 35v fails the relay won't pull in, it MIGHT buzz quietly. The current through R4, R3, the relay and Q2 isn't enough to pull in the relay, so C1 across R3 gives it the extra pull in "kick".

Thanks for the help qguy and markthefixer as it is much appreciated. I have insulated the DMM and will take readings later today and i'll confirm pin 5, and 8 and retry to get a reading on pin 3. Im nerveous about taking the readings on PA3004 even with the insulation tho.

What's the trick to taking the readings on the Pa3004 IC. The probe leads don't want to fit under the body of the ic chip. Do you test from the foil side? get a smaller probe?

you could take readings from the nearest component that connects to the relevant pin .
just look at the schematic ,
examples ....
pin 1 connects to post 9 .
pin 3 base of q2 .
its that or gently bending the ic gently to see the pins .that's if it is mounted high enough to bend safely .

the only awkward one is pin 8 as it connects to c4 and c5 so will need measuring on the ic pin or under the board .

I've measured

Q2 (the one closest to the edge of the board).
The bottom left prong reads 0 to .01,
Bottom right prong reads 0 to .01
Top prong reads .75. (This must be the Base)

Q1 reads:

Bottom Prong 13.7v
top left prong read 5 to .1. Now is reading -0.2
top right prong reads 1.39V. Now is reading 13.95

Confirmed that pin 3 reads 0 to .1 (switched DMM to AC)
Confirmed that pin 5 reads 0 to .1
Confirmed that pin 8 reads 0 to .1

On PA3004

was only able to get DMM leads to measure pin #8. for fear of shorting it out. (won't fit under the chassis of chip)
1
2
3
4
5
6
7
8 7.2V 7.2V

Thanks petehall347. I see the schematic. Quick question....Where should I test 4, 5 and 6, and 7 safely?

PA3004 Readings

VA3004 Readings


I managed to take a few readings but am still unsure of where to take the readings from on some of the below posts.

1 13V 13.36
2 No reading
3 1.0 .75 read from base of Q2
4 0v Where to test?
5 0v Where to test?
6 -7V Where to test?
7 Ac .75V Where to test?
8 7.2V 7.2V

looks like Q2 is bad, the base voltage says "TURN ON!!", and it isn't.

need all three q2 voltages, to see if relay and resistors are passing (some) current.

markthefixer said:

looks like Q2 is bad, the base voltage says "TURN ON!!", and it isn't.

need all three q2 voltages, to see if relay and resistors are passing (some) current.

Click to expand...

I'll retry to get readings from q2. As seen the readings were nill from 2/3 posts. Only the base shows some voltage.

Confirmed

Q2 (the one closest to the edge of the board).
The bottom left prong reads 0 to .01,
Bottom right prong reads 0 to .01
Top prong reads .75. (This must be the Base)

Now what? I don't know how or where to continue testing each post on PA3004. Where should I test 4, 5 and 6, and 7 safely? See Post #8 Above.


Thanks again.

pin 4 ..junction of r1 r7 r5 r6 .....
pin 5 ..same as board pin 3
pin 6 ...r10 ..you need to see which end goes to the ic
pin 7 r8 ....you need to see which end goes to the ic


also voltage at board pin 10
if board pin 10 measures like 76v get voltages for each side of r3 and r4 .
also try your meter across d2 and measure voltage .

just seen from earlier post the voltage is up at board pin 10 so just measure at the resistors r3 r4

petehall347 said:

pin 4 ..junction of r1 r7 r5 r6 .....
pin 5 ..same as board pin 3
pin 6 ...r10 ..you need to see which end goes to the ic
pin 7 r8 ....you need to see which end goes to the ic


also voltage at board pin 10
if board pin 10 measures like 76v get voltages for each side of r3 and r4 .
also try your meter across d2 and measure voltage .

just seen from earlier post the voltage is up at board pin 10 so just measure at the resistors r3 r4

Click to expand...

1 13V 13.9
2 No reading
3 1.0 .8
4 0v .8
5 0v 0
6 -7V -7.6
7 Ac .75V .3
8 7.2V 7.2V


Pin 10 was at 76, now 81.2V
Correction D2 81.2
other side 68.0

get voltage across d2 ...

Correction D2
Top of resister 81.2
Bottom of resister 68.0
r3 r4
Top of resister 38.8
Bottom of resister 67.9

Summary of the Readings:

awr-152

pin 22 +60v *+65.2v*
pin 23 +23v *+25.4v*
pin 29 -13v *went back and forth -17v to -35v*
pin 25 -23v *-23.8v*
pin 27 -60v *-64.8v*
pin 16 +13v *+13.93v*
pin 19 +76v *+80.3v*

awm-120

pin 5 0.000v *0.0v*
pin 8 0.000v *0.0v*
pin 2 -60v *-64.6v*
pin 3 21v AC - Wasn't able to make this reading (i believe it's an AC reading per the other threads)
pin 9 +13v *+13.7v*
pin 10 +76v *+80.7v*
pin 4 +12v or so. *12.4v*

PA3004

1 13V 13.9
2 No reading
3 1.0 .8
4 0v .8
5 0v 0
6 -7V -7.6
7 Ac .75V .3
8 7.2V 7.2V


Pin 10 was at 76, now 81.2V
Correction D2 81.2
other side 68.0

Q2 (the one closest to the edge of the board).
The bottom left prong reads 0 to .01,
Bottom right prong reads 0 to .01
Top prong reads .75 (This must be the Base)

D2
Top of resister 81.2
Bottom of resister 68.0
r3 r4
Top of resister 38.8
Bottom of resister 67.9

relay should be turned on then . do you not hear it click ? try holding your finger on it to see if it clicks after turning the amp on .

i did want you to put black meter lead to one side of d2 and red meter lead to the other side and measure the voltage . but if i am diagnosing your readings of r3 correctly the relay ought to be switched on .it might be bad inside the relay .

PA3004

1 13V 13.9
2 No reading
3 1.0 .8
4 0v .8
5 0v 0
6 -7V -7.6
7 Ac .75V .3
8 7.2V 7.2V

i doubt pin 4 is 800mv .... but dont worry about this for now

D2is reading .01 when i measure it with the black lead on bottom of the resister, red lead on top. The relay is clicking off and on every 10 seconds or so.I can test pin 4 while this is happening and it's reading .7 to .8 then, when it clicks off/on again reads .0