Pioneer SX-1280 Protection Relay not Clicking

C

Craftsman11

AK Subscriber
Subscriber
Hello:

I've been restoring a SX-1280 that did not work when I got it. Someone has worked on this before me so I am basically going through the whole unit step by step to get it back in working condition. I have rebuilt the power supply board and the protection boards per the BOM shared in other threads. I also installed new filter caps. The unit powers on and the soft start relay clicks but no click from the protection relay. The preamp works--verified through a different unit with the jumpers removed. I also rebuilt both amp boards only to the extent recommended in the BOM thread so there are transistors that are still original. I have a DBT and have recorded the following voltages. Your help in verifying these voltages are correct as well as any suggestions as to whether or not to move on to the amp boards would be appreciated. Thanks!

AWR-157 Power Supply Voltages
Pin 1 |65.7
Pin 2 |65.6
Pin 3 |--
Pin 4 .6 mv
Pin 5 |--
Pin 6 |60.6
Pin 7 |60.6
Pin 8 |66.8
Pin 9 |--
Pin 10 |--
Pin 11 |32
Pin 12 |32
Pin 13 |32
Pin 14 |9.3
Pin 15 |9.3
Pin 16 |13
Pin 17 |13
Pin 18 |13
Pin 19 |-3.1
Pin 20 |-33.5
Pin 21 |-33.5
Pin 22 |-33.5
Pin 23 |Ground
Pin 24 |--
Pin 25 |-72

AWM-123 Protection Assembly Voltages
Pin 1 |56.4
Pin 2 |56.4
Pin 3 |76.5
Pin 4 |-76.5
Pin 5 |0
Pin 6 |0
Pin 7 |0
Pin 8 |0
Pin 9 |-76.4
Pin 10 |76.4
Pin 11 | 0
Pin 12 | 0
Pin 13 | -3mv
Pin 14 | -22mv
Pin 15 |-8mv
Pin 16 |-25mv
Pin 17 |13
Pin 18 |12.5
Pin 19 |12.5

Thank You.
 
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Going off memory here
Awr-157 is +/-68, +/- 32, +13 dcv
Do they match the schematic? within tolerance?
Look at voltages on the pa3004 chip and the relay driver 2sc1384? too

Good luck
 
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AWM-123 Protection Assembly Voltages
Pin 1 |56.4 ACv in
Pin 2 |56.4 ACv in
Pin 3 |76.5 good
Pin 4 |-76.5 good
Pin 5 |0 ground
Pin 6 |0 ground
Pin 7 |0 ground
Pin 8 |0 ground
Pin 9 |-76.4 good
Pin 10 |76.4 good
Pin 11 | 0 ACv in
Pin 12 | 0 ACv in
Pin 13 | -3mv left channel in
Pin 14 | -22mv left channel relay switched out
Pin 15 |-8mv right channel relay switched out
Pin 16 |-25mv right channel in
Pin 17 |13 power feed in
Pin 18 |12.5 overcurrent protect left channel when pilled low
Pin 19 |12.5 overcurrent protect right channel when pulled low

no problems with the incoming voltages and signals.

check q1, measure base of Q2, if over 0.6v the relay should be pulling in.
replacements:
q1 ksc1845
q2 ksc2690
 
Thanks for your help.

Q1 12.5v at E
Q2. 3.0mv at base

Perhaps D3 is the culprit? If so, please verify the sub: IN 5243 or IN 5234? I have both on hand so I may have installed the wrong one.
 
Mark:

Looking at the schematic and not the foil side drawing for AWM-123 Protection Board, I can now see that Q2’s base is connected to Pin 3 of the PA3004.

I’d still appreciate verification on D3’s proper sub but I need to measure voltages on the PA3004 and report back. Thanks!
 
Hello:

Here are my PA3004 voltages on DBT vs schematic values:
Pin| mine schematic
Pin 1| 12.6 12.5
Pin 3| 5mv. .7v
Pin 6 | -7v -7v
Pin 7| .59v .7v ac
Pin 8.| .46v. 7.2v

Obvious problem on Pins 3 and 8. I checked for cold solder joints and point to point continuity. Does anyone have suggestions on how to further troubleshoot this chip? Thanks.
 
D3 is a 13v zener diode. 512-1N5243B

pin 8 is the capacitor, that charges up when the chip is happy with it's inputs.
pin 3 is an output. as of that voltage measurement the chip is not charging it's timing capacitor.

.59v vs 0.7v ac, ac may be low, parallel a 1 meg across R10 and see if the voltage comes up a bit.
R9 MAY be 680k but the input acts like a 10k resistor.
before you do that, take it off that d* DBT. It's long past the stage of needing it for shorted outputs.
 
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Hello. New voltages with the 1M paralleled across R10 under “new” column. Pin 7 went up a bit. Pin 3 went down a bit. Please advise. Thanks.

Pin| mine schematic new
Pin 1| 12.6 12.5 12.5v
Pin 3| 5mv. .7v. 2.5mv
Pin 6 | -7v -7v. -7v
Pin 7| .59v .7v ac. .7v AC
Pin 8.| .46v. 7.2v. .46v
 
well, ok. Lets talk about the PA3004 chip a bit:

pin 1 is the 13v power feed, if it gets down to under 11 volts, things start getting goofy.
pin 2 is not present

pin 3 is the relay driver output. It starts out at low volts (usually under 0.1v) and will put out +0.7v or a bit more when it wants the relay on.

pin 4 is the dc detector, R1 & R2 (75k) sum the outputs of the left and right channels, integrate it in a 100 uF cap C4, along with R8 (11k) to provide a constant emptying of the capacitor. This emptying has no relation to the pin 8 sawtooth.

There's an added complication, Q1. It is set up so that the over current detectors on either or both power amplifiers can pull down the base of the PNP transistor (D1, R3 (13k), R4 (10k)and turn it on, sending current through R7 (1.3k) into the DC detector input - thus effecting a protect trigger.
These over current detectors come in on pins 18 & 19. From Q14 on each amplifier card.
a shorted C16, or a leaky Q14 can give false signals to Q1.

pin 5 is the ground

pin 6 is the -7v power sensing (and using?) input. -76v comes into the board, R17 (3.6k 2w) acts as a divider / load for zener diode D3 (13v).
C2 22 uF smooths the zener voltage. R12 is a 750 ohm series resistor that takes the -13v from D3, and drops it down to -7 volts. C5 10 uF smooths the -7v from internal current demands by acting as a reservoir. -13v to -7v across 750 ohms implies a 6.67 milliampere current draw.

pin 7 is the AC voltage detector, supposedly getting 0.7v AC voltage. Ac voltage through the R10 (1.8 meg) and R9 (680k) voltage divider - which if that were calculated is far in excess of 0.7 volts... The AC input pin acts like a 10,000 ohm resistor to ground. This gets the AC volt voltage divider calculation closer to reality.

Pin 8 is the timing capacitor C16 (33 uF), there will be a sawtooth waveform which prevents the capacitor charging to the trigger point. When the sawtooth stops, the cap starts charging the time delay to reach the trigger point and turn on the relay through pin 3.

all your voltage readings have omitted pin 4. A pretty important pin,but I don't know what voltage above zero upsets it.

If Q1 is removed, there is no overcurrent protect, But two Q14's and Q1 then cannot bollix up the works.

I don't remember if I asked you to pull Q1, it is a common step and I have gone through this so many times. It's late and I can't reread the thread tonight.

Usually I just shotgun them, new C16s using film caps,
2x ksc1845 into the Q14's
and a ksa992 into Q1.
Q2 is usually a ksc2690
New reliable parts.

Then if protect triggers, I KNOW it has a valid reason.
 
Wow. I couldn’t have asked for more comprehensive, succinct guidance to this issue. Thank you so much for your time and generosity.

I followed your explanation, checked each component and measured voltages along the way. Q1 was suspect so a fresh 992 was installed. Also, I had substituted C4 with a 100/50 so I removed and installed a 100/25 instead (parts are so hard to come by right now and I only had the 50v). That seemed appropriate because of the complexity. All resistors were spot on.

You were right. Pin 4 was reading 1.7v when not working. Now it has -41mv with relay engaged. All other voltages on the chip are within tolerance.

Anyone with passion who has busted their ass on a unit like this knows that feeling when it finally clicks (literally and figuratively). I was so happy in the solitude of my garage shop when the relay finally clicked. It’s still a little long on engagement but the unit does go past protection and music is playing! Still need to take care of offset, bias and preamp restoration but thank you, thank you and gracias Mark!
 
Also, should I leave that 1M in parallel across R10? It’s working but didn’t know if that was for troubleshooting only.
 
I'd remove it and see what happens. It will drop the amplitude, but will that hurt?
 
Hi Mark. I removed the 1M resistor and all is well. Now, on to my next adventure. The Aux has very weak output when connected to an iPhone music source but the tuner is working well. Thanks again for your help with the amplifier and protection. I’ll reach out if I run into any obstacles. Thanks!
 
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