SX-1080 - Protection at high volume

Barkingshins

Barkingshins

New Member
In the last 8 months or so, I have managed to purchase and refurb three vintage Pioneer receivers without incident... an SX-1250, an SX-950 and an SX-650, in that order. Thanks in no small part to the people and information here at AK, all three now look and sound amazing.

Most recently I purchased a very nice SX-1080 from a co-worker and have just wrapped up the refurb including a thorough cleaning, recap, new indicator and dial lights, bias/offset adjustments, etc. Once everything was back together and I had connected my 8Ω dummy loads, I powered it up and started putting it through its paces. This is the issue I've discovered...

With a 1kHz sine wave on the inputs at 150mV, the receiver is a champ until the volume gets to about the -8db hash mark... roughly 3 o'clock on the dial. At this point the protection circuit kicks in and shuts down the outputs. This has been the case with both a sine wave on the AUX input as well as just FM radio broadcasts. If I back off the volume, after a few seconds the units drops out of protection and the outputs come back to life.

Unfortunately, my testing before beginning the refurb was not so thorough. As such, I can't say whether or not this is a pre-existing issue.

One thing to note: I have NOT replaced either of the protection relays in this unit; both are original as far as I know.

Can one of the experts around here shed some light on what is going on here and guide me through troubleshooting this issue? I can source, remove and replace components with the best of 'em, but troubleshooting is not my strong suit. I have a good Fluke RMS meter and Tek analog scope at my disposal as well as all the tools that I can imagine needing for this.

Any help at all would be appreciated. Thank you!
-Brian
 
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slow_jazz said:
That's really pushing it.

Good luck...
Click to expand...
For sure! This is waaaay louder than I would ever have it with speakers connected. However, all of my X50's had no problem going to max volume during testing. There's something going on here and it's going to bug the hell outta me if I don't get it resolved... especially since this is one I intend to try and sell. I need to be able to honestly say that the unit is tip-top and right now, I can't.
 
txturbo said:
What is the peak power as read by the power meters on 1080 before it shuts down?
Click to expand...
It generally cuts out just short of 0dB or 120W. I assume that this isn't by design since the procedure for calibrating the VU meters in the service manual actually has you feed in a 1kHz sine wave and adjust the level for 31VAC at the output. It usually cuts out before I get to 31V... just before.
 
So, are the bias and DC offset set to spec?
If you have a scope see if the output is clipping at your max volume.
 
The above. If it's clipping/tossing out DC, there you go. Does the protection section have any possible adjustments? On the 20 series there's a trimmer to control the cutoff somewhat is why I'm asking.
 
If you have a scope you can look at the source of the triggering. Look at pin 4 of the PA3004 on AWM-120. it will be momentary so you may require a digital scope to catch it happening.
I noticed that they are using a polarized ecap for C2, I would suggest a BP ecap for this app.
Q1 turns on in the event of an over current condition. Base gets pulled low by the balanced bridge,Q8 on the PA ckt.(AWM-071)
I also like to use a film cap for C11 on AWM-071
 
Thank you for the guidance.
I'm at the vet right now with my wife and our puppy, Vincent, who apparently broke his leg in a fall off the bed this morning. :(
Once he's been taken care of and things have settled down a bit, maybe later tonight, I'll go through your suggestions with the scope and get back to you.
Until then, thanks again.
 
Well, I'm disappointed to say that things have gone from bad to worse. Whereas before it seemed to only go into protection at high volume, now it is going in and out of protection at random intervals (every few minutes at least) at no volume whatsoever and without outputs A or B even turned on. Doesn't seem to matter which input is selected either. *sigh*

Bias and DC are both within 1 or 2 mV of spec.

It definitely wasn't doing this before the recap so I think it's safe to assume that this is my doing.

Here's my full recap list. It probably makes sense to start there and eliminate the possibility that I've swapped in something wildly inappropriate for its function. I did have to make several substitutions as some items were no longer available. I'm especially concerned about my choice of sub for the now-obsolete 512-1n4004 on the Power Supply Assembly.

Have a look...

<GWS-125 Function and Equalizer Assembly>

C3 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C4 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C9 470 6 CEA 470 16 647-UPW1E471MPD
C10 470 6 CEA 470 16 647-UPW1E471MPD
C11 100 25 CEA 100 35 647-UPW1V101MPD1TD
C12 100 25 CEA 100 35 647-UPW1V101MPD1TD
C17 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C18 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C19 220 6.3 CEA 220 10 647-UPW1A221MED
C22 10 16 CEA 10 50 647-UPW1H100MDD

<GWG-112 Flat Ampifier Assembly>

C3 0.1 35 CSZA 0.1 63 80-F612JF104J063L
C4 0.1 35 CSZA 0.1 63 80-F612JF104J063L
C5 1 25 CSZA 1 50 647-UKL1H010KDDANA
C6 1 25 CSZA 1 50 647-UKL1H010KDDANA
C13 100 10 CEANL 100 35 647-UKL1V101KPDANA
C14 100 10 CEANL 100 35 647-UKL1V101KPDANA
C15 100 10 CEANL 100 35 647-UKL1V101KPDANA
C16 100 10 CEANL 100 35 647-UKL1V101KPDANA
C17 100 25 CEA 100 35 647-UPW1V101MPD1TD
C18 100 25 CEA 100 35 647-UPW1V101MPD1TD
C19 4.7 25 CEANL 4.7 50 647-UKL1H4R7KDDANA
C20 4.7 25 CEANL 4.7 50 647-UKL1H4R7KDDANA

<AWG-056 Tone Control Assembly>

C1 4.7 25 CEANL 4.7 50 647-UKL1H4R7KDDANA
C2 4.7 25 CEANL 4.7 50 647-UKL1H4R7KDDANA
C3 4.7 25 CEANL 4.7 50 647-UKL1H4R7KDDANA
C4 4.7 25 CEANL 4.7 50 647-UKL1H4R7KDDANA
C17 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C18 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C19 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C20 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C21 100 10 CEA 100 10 647-UPW1A101MDD
C22 100 10 CEA 100 10 647-UPW1A101MDD
C23 47 35 CEA 47 35 647-UPW1V470MED
C24 47 35 CEA 47 35 647-UPW1V470MED
C25 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA
C26 2.2 50 CEANL 2.2 50 647-UKL1H2R2MDAANA

<AWT-001 Filter Assembly>

C1 0.47 35 CSZA 0.47 63 80-F612JG474J063C
C2 0.47 35 CSZA 0.47 63 80-F612JG474J063C

<GWS-124 Speaker Selector Assembly>

C1 4.7 6 CSZA 4.7 50 647-UKL1H4R7KDDANA
C2 33 10 CEA 33 35 647-UPW1V330MDD
C3 4.7 6 CSZA 4.7 50 647-UKL1H4R7KDDANA
C4 33 10 CEA 33 35 647-UPW1V330MDD
C5 100 6 CEA 100 10 647-UPW1A101MDD

<AWH-071 Power Amplifier Assembly> x2

C1 2.2uf 50v & C2 2.2u 50v replaced with one low leakage cap 667-ECQ-E1105KF
C11 0.22 25 CSSA 0.22 250 667-ECQ-E2224KF

D1 1s2471 512-1N4148
D2 1s2471 512-1N4148
D6 1s2471 512-1N4148
D7 1s2471 512-1N4148
D3 SIB01-02 512-UF4004
D4 SIB01-02 512-UF4004

VR1 100 ohm single turn trimpot 652-3386H-1-101LF
VR2 150k multi-turn trimpot - 652-3296P-1-254LF

<AWR-152 Power Supply Assembly>

C11 220 100 CEA 220 100 647-UPW2A221MHD
C12 220 100 CEA 220 100 647-UPW2A221MHD
C13 220 35 CEA 220 35 647-UPW1V221MPD6
C15 220 80 CEA 220 100 647-UPW2A221MHD
C16 220 80 CEA 220 100 647-UPW2A221MHD
C17 47 16 CEA 47 16 647-UPW1C470MDD
C18 47 16 CEA 47 16 647-UPW1C470MDD
C19 4.7 50 CEA 4.7 50 647-UPW1H4R7MDD
C20 4.7 50 CEA 4.7 50 647-UPW1H4R7MDD
C23 2200 35 ACH-060 2200 35 647-UPW1V222MHD
C24 47 25 CEA 47 25 647-UPW1E470MDD
C25 47 25 CEA 47 25 647-UPW1E470MDD

D1 10E2 400v 1A 625-1N4004GPE-E3/54
D2 10E2 400v 1A 625-1N4004GPE-E3/54
D3 10E2 400v 1A 625-1N4004GPE-E3/54
D4 10E2 400v 1A 625-1N4004GPE-E3/54
D6 10E2 400v 1A 625-1N4004GPE-E3/54
D7 10E2 400v 1A 625-1N4004GPE-E3/54
D8 MZ140 512-1N5244B
D9 MZ130 512-1N5243B
D10 LZ230 512-1N4748A
D11 LZ230 512-1N4748A

<AWM-120 Protection and Surge Killer Assembly>

C1 220 35 CEA 220 35 647-UPW1V221MPD
C2 100 16 CEA 100 35 647-UPW1V101MPD1TD
C3 10 16 CEA 10 50 647-UPW1H100MDD
C4 47 16 CEA 47 16 647-UPW1C470MDD
C5 47 16 CEA 47 16 647-UPW1C470MDD
C6 1 80 CEA 1 100 647-UKL2A010KDD

D1 MZ-130 512-1N5243B
D2 1s2471 = 512-1n4148
D3 1s2471 = 512-1n4148

Q1 2sa733 to-92 ecb 512-KSA1013YBU

Q2 2sc1438 to-92 ecb 512-KSC2690AYS

<Miscellaneous>

ACH-085 C7 22000 100 661-E36D101N223TDB7M
ACH-085 C8 22000 100 661-E36D101N223TDB7M
CEA 010P 80 C9 1 80 CEA 1 100 647-UKL2A010KDD

Thank you.
Brian
 
I'd suspect that something has gone awry since your initial high power testing.
I'd look for capacitors put in backwards and test the transistors - especially on the protection board.
What did you sub for the 1N4004? That variant with no suffix letter is an old number but there are lots of newer versions available - search Mouser for "1N4004".
 
w1jim said:
I'd suspect that something has gone awry since your initial high power testing.
I'd look for capacitors put in backwards and test the transistors - especially on the protection board.
What did you sub for the 1N4004? That variant with no suffix letter is an old number but there are lots of newer versions available - search Mouser for "1N4004".
Click to expand...
Thanks for the help. Yes, it would certainly appear that something has gone awry.
I've been over the protection board as well as the power supply assembly and power amps looking for backwards caps but everything looks good. As for testing the transistors, I have a handy Atlas DCA55 semiconductor tester that I test all diodes and transistors with before they go into circuit. If I am to re-test them, do I need to pull them out of circuit?
My choice for the 1N4004 is in the parts list I posted last night - Mouser p/n: 625-1N4004GPE-E3/54. I did exactly what you said and searched for available variants on the 1N4004 and chose one that seemed to best match the specs of the original... but I only kinda, sorta know what I'm doing. :)
 
Scope your output. I suspect the 1080 is clipping around the 3 o'clock position. And the protect circuit is doing what its designed to do.
 
Barkingshins said:
See my post #12...
Yesterday it started going in and out of protection with no output at all.
Click to expand...
Go over your work with a bright light and a magnifier... Look for cold iffy solder connections and solder bridges on the power supply board and the protect board.
 
Question, was Q8 replaced on both power amp boards (AWH-071)?

Edit: corrected numbers
 
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