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Pioneer SX-880 LED Indicators won't work

HiFiRyan

HiFiRyan

New Member
Hi everyone!, new guy to the forum here. I recently picked up a SX-880 and have repaired it to the point that everything is working except the LED indicators.
I eventually want to install a rebuild kit, but would like to fix this issue first. I've found that the LEDs have a good ground but supplied voltage to them is 1.4 - 1.6v.
PA1001A is only receiving 5.9V (should be 13V on the diagram I have)
Q26 Transistor has C=50V E=6.3V B=6.9V
Q30 Transistor has C=59V E=22V B=22.6V

I'm not too sure what to test next or what could be causing these voltages to be off. Any help would be greatly appreciated.

Thanks!
 
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The PA1001A should have a 13V supply on Pin 1, and a 5.7V supply on Pin 8. Verify that the device is oriented correctly - The dimple in the top of the plastic package is typically placed adjacent to Pin 1 as a reference.

On the other hand, Q26 seems to have a problem. It might be worthwhile to check D28 (a 14V zener) to see if it is damaged. That should be providing 14V to the base of Q26. The supporting components, R407 and C410, could also be affecting that.

Q30 could also be affected by a failure of D28 since it would be pulled down by Q28.
 
Thanks Watthour! and thanks for the quick reply! I double checked that I knew where Pin 1 of PA1001A is and I'm getting 6.1V there. I''m also only seeing 3.5V on Pin 8

Newbie question: Would I have to pull D28, R407, and C410 off the board to test?
 
It would be more accurate to have components out of circuit for testing, but simply lifting one end of R407 should reveal whether it has drifted in value, and might isolate the remainder of the circuit well enough to determine if something else is damaged. Testing D28 (the 14V zener) with an ohmmeter would only provide a "go / no-go" indication, and would not necessarily reveal where it is regulating.

If the D28 and C410 are going to be removed, they might as well be replaced. C410 can be anything from a 100µF to 330µF as long as they are rated 16V or higher.
 
I pulled D28 and tried the diode test function on my multimeter, it tested good (current only flowing in one direction). However, It seemed to show current flow in both directions when testing with 200k ohm scale on the multimeter. Would this mean it has failed?
I see in the parts list that D28 is a MZ-140, which is a discontinued part number. What is the best/ most common replacement part to use for this?

R407 tests out at 6.19kohms,which is good.

I'll have to get some orange ceramic disc capacitors if I'm going to remove/ replace C410
 
I should also mention that I replaced D8 in this receiver. After changing bulbs one of the sockets wasn’t secured and fell onto the board, taking out D8 before popping the lamp fuse. Oops!
D8 was a 10E2 that I replaced with a 1N4004. I read somewhere on here that this was a suitable replacement. Not sure if this is related.
 
HiFiRyan said:
I pulled D28 and tried the diode test function on my multimeter, it tested good (current only flowing in one direction). However, It seemed to show current flow in both directions when testing with 200k ohm scale on the multimeter. Would this mean it has failed?
Click to expand...

A zener will indicate current both ways at a given voltage level. A rudimentary ohmmeter test would only reveal whether it is open or shorted, but will not verify its point of regulation unless the meter test voltage is close to the rated regulating point of the device.

I see in the parts list that D28 is a MZ-140, which is a discontinued part number. What is the best/ most common replacement part to use for this?
Click to expand...

A generic 14V zener will work, such as the 1N4743, 2EZ14D, BZ-140, NTE144, among others.

I'll have to get some orange ceramic disc capacitors if I'm going to remove/ replace C410
Click to expand...

I would think that a ceramic disc with a 100 or 220µF rating will be difficult to find. An electrolytic is more suitable.
 
Ok great, thanks! I'll stop into our electronic supply tomorrow and grab some things. Hopefully have them soldiered in this weekend :)
 
I was able to order and soldier in replacements for D28 and C410. Still no luck. I remeasured Q26, it has the same readings. I measured Q28 and have C= 22.5V E=7V B= 7.6V
I'm wondering where the 42.1V that the collector of Q28 is supposed to have originates? I trace it back to the output transistors location, but I'm not too sure on this area of the schematic.
 
The 42V (approximately) is sourced from the 2SK34 FET (Q24) as a regulator. The current through the FET is low, but is only intended to provide a few mA as a reference source for Q28, and the supply for the Q30 collector. If Q28 and/or Q30 were damaged or driven into hard conduction, the FET might not have been able to handle the current and failed.

Just about any N-channel FET rated for 20V or better should work, but the drain current should be at least 10mA and device should be able to handle ¼ watt or better. A BF256 (or 256B) could work if you have some stock. This one also might just get it done.
 
Ok interesting! I was wondering the purpose of Q24. I'll have to see what I have in stock for a replacement, or make an order. Thanks again!
 
Looking at the data sheet for the 2SK34, with the 14-15V drop from drain to source it seems that the jFET would act like something around 500Ω at that voltage - I think. That is probably no so relevant, but should demonstrate how a lower voltage rated device could survive as long as something doesn't increase the voltage difference beyond its rating, like Q28 going stupid. Unfortunately, a lot of jFETs have disappeared from the market, and the present selection is limited.
 
I'll have to make an order as I have no jFETs. It appears Onsemi is still making BF256B. I'd also like to replace Q28 (2SC945A-QorP) and Q30 (2SD325R-DorE) but I'm having a hard time finding good cross reference information. I wouldn't mind replacing Q26 (2SD712-CorD) as well. I've added a better heatsink but it shows signs of having been quite hot.

Are there any other components you'd recommend testing or ordering?
 
I replaced Q24 with a BF256B, Q28 with a KSC945C (pin rearranging required) , and while i was in there I swapped out Q26 and Q30 with a KSC2073, and Q27 with a KSA940TU
Powering back up I now have my LED indicators working properly! :D

I now have 13V on pin 1 of PA1001A
I measured voltages at Q26 C=41.1V E=13.7V B=14.3V
and Q30 C=58.6V E=14.5V B=15.1V

Im curious to why the low voltages on Q30 and is it worth tracking this issue down?
 
Ive also tried to set the DC balance to 0V and can only get down to 32mV (P + Q jumpers removed)
And I cant get the L + R bias higher than 3mV ( should be 30mV)
... man i wish my readings were reversed XD
 
I'm wondering what would cause the power supply circuit to have +/- 14V instead of the +/- 41V it should have?
 
I've finally finished sorting out and recapping the SX-880!
First off the KSC945C I'd put in for Q28 wasn't up for the challenge. I tested and reinstalled the original transistor.

I'd also found that Q37 in the protection circuit tested bad, it had free flow at Base to Collector, and the Emitter remained open.
Somehow the protection relay was able to ground at the PA3004?, Strange. I replaced Q37 with KSC2383YTA and the protection circuit is working properly.

I did a full electrolytic recap of the main board with Elna Silmic IIs, and set the DC balance & idle current.

Now I'm spinning some Stones :D

Thanks to everyone that helped with answering my questions.
 
I dislike the c945, too many people install it wrong.
It is the single most mis-installed transistor here.
that's why I recommend it's brother: ksc1845.

The original 945 is ecb if it is from japan, it is ebc if it is from the USA.
Fairchild's ksc945c is ecb, while the ksc945 is ebc.


:thumbsup:
 
I though I had all the pins correct. I pulled up data sheets for for the old and new transistor but maybe I had the wrong sheet.
Theres a lot of options for pins on that one! I'll checkout the KSC1845.
Thanks!
 
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