Author |
Message |
stratozen
|
Post subject: Pioneer sx-1050 HeadAche Posted: May Sat 26, 2018 9:49 pm |
|
Joined: Apr Wed 03, 2013 2:38 pm Posts: 103
|
Problem: Power on, Tune to a station, low volume, sounds great
Turn volume up past a certain level, cuts out until you back the volume level down then it comes back on.
Heres what I've done so far:
Downloaded service manual from Hi-Fi Engine, and singled out the Protection Circuit board.
Checked all transistors and replaced 3 that were bad, including Q1 and Q2 which were mentioned in threads before as always being suspect when this problem occurred before, recapped all capacitors with new, checked all resistors and diodes.
Now I'm kinda stuck as I figured that would be where the problem was.
Any help would be appreciated
|
|
Top |
|
 |
pixellany
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sat 26, 2018 10:17 pm |
|
Member |
 |
Joined: Jul Mon 26, 2010 8:30 pm Posts: 29191 Location: Annapolis, MD
|
No time right now, but one easy check: monitor relevant voltages and see if the protection circuit is shutting it down. ....or temporarily bypass the protection circuit
First option preferred.
I assume both channels are quitting.....if so, that points to the protection circuit.....or any other element that is common to both channels...like a power supply.
_________________ -Mark "Voltage is fun to watch, but it's the CURRENT that does the work."
|
|
Top |
|
 |
Johnnysan
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 1:09 am |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 16749 Location: Albuquerque, NM 87123
|
I would check bias adjustments.
|
|
Top |
|
 |
Don Cavey
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 1:23 am |
|
Member |
 |
Joined: Jan Thu 01, 1970 1:00 am Posts: 12209 Location: Fernandina Beach, FL
|
Johnnysan wrote: I would check bias adjustments. But if the bias is off, why? I agree but you might want to find out why (IF) the bias is off. Electrolytic capacitors etc...
_________________ Don
|
|
Top |
|
 |
Johnnysan
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 2:23 am |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 16749 Location: Albuquerque, NM 87123
|
Don Cavey wrote: Johnnysan wrote: I would check bias adjustments. But if the bias is off, why? I agree but you might want to find out why (IF) the bias is off. Electrolytic capacitors etc... Poster has already said he replaced/checked resistors, capacitors, transistors and diodes. What else is left? The bias adjustments. Nuff said?
|
|
Top |
|
 |
Don Cavey
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 7:01 am |
|
Member |
 |
Joined: Jan Thu 01, 1970 1:00 am Posts: 12209 Location: Fernandina Beach, FL
|
Johnnysan wrote: Don Cavey wrote: Johnnysan wrote: I would check bias adjustments. But if the bias is off, why? I agree but you might want to find out why (IF) the bias is off. Electrolytic capacitors etc... Poster has already said he replaced/checked resistors, capacitors, transistors and diodes. What else is left? The bias adjustments. Nuff said? You're right. Somehow I missed that... Sorry.
_________________ Don
|
|
Top |
|
 |
stratozen
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 1:53 pm |
|
Joined: Apr Wed 03, 2013 2:38 pm Posts: 103
|
Thank you for the replies. Upon closer inspection it looks like the power amp board has been removed some time before. With the concensus that there could be a problem with the bias I have decided to remove the power amp board and replace the (4) 470 uf orig electrolytics and check/and or replace transistors.
Is there a way to clean the bias controls while accessible?
|
|
Top |
|
 |
pixellany
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 2:11 pm |
|
Member |
 |
Joined: Jul Mon 26, 2010 8:30 pm Posts: 29191 Location: Annapolis, MD
|
I'm missing the logic for the bias theory.....is the bias adjusted separately for the two channels? If so, then we would need two failures for both channels to quit. Also, how would a bias problem cause the observed symptoms?
_________________ -Mark "Voltage is fun to watch, but it's the CURRENT that does the work."
|
|
Top |
|
 |
stratozen
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 4:46 pm |
|
Joined: Apr Wed 03, 2013 2:38 pm Posts: 103
|
According to the service manual each channels bias is adjusted by (2) bias controls on the power amplifier board. The (4) 470uf caps all checked about 595uf so they will be replaced but I don't think this is the area of my problem, I don't know where to look,really. just for the record both channels do shut down.
|
|
Top |
|
 |
Don Cavey
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 5:25 pm |
|
Member |
 |
Joined: Jan Thu 01, 1970 1:00 am Posts: 12209 Location: Fernandina Beach, FL
|
stratozen wrote: According to the service manual each channels bias is adjusted by (2) bias controls on the power amplifier board. The (4) 470uf caps all checked about 595uf so they will be replaced but I don't think this is the area of my problem, I don't know where to look,really. just for the record both channels do shut down. Did you check the value of the 470 ufd capacitors with a digital meter? Or were they tested with a capacitor tester, something like a Heathkit C-3 or EICO 950B? Reading high with a digital meter is sometimes suspect, as in they are actually going bad.
_________________ Don
|
|
Top |
|
 |
stratozen
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 6:16 pm |
|
Joined: Apr Wed 03, 2013 2:38 pm Posts: 103
|
Caps were checked with a digital Pretty sure they are the orig so I'm going to replace with new wish I knew with a little certainty I am in the right area before I start pulling transistors but it's good I pulled that board cause the last removal they just cut the wires and then resoldered Took me 1/2 hour to unwind the old off the 20 pins
|
|
Top |
|
 |
Don Cavey
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 6:21 pm |
|
Member |
 |
Joined: Jan Thu 01, 1970 1:00 am Posts: 12209 Location: Fernandina Beach, FL
|
I would certainly suspect capacitors before transistors.
_________________ Don
|
|
Top |
|
 |
pixellany
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 7:50 pm |
|
Member |
 |
Joined: Jul Mon 26, 2010 8:30 pm Posts: 29191 Location: Annapolis, MD
|
If the bias settings are separate for each channel, it does not seem likely that this would cause the issue. BUT--why not try it?
I would be looking for things that are common to both channels.
there was discussion of the protection circuit---can someone summarize how it works?
_________________ -Mark "Voltage is fun to watch, but it's the CURRENT that does the work."
|
|
Top |
|
 |
radiotechnician
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 8:39 pm |
|
Joined: Sep Thu 23, 2010 6:37 am Posts: 12437 Location: Powell River BC Canada
|
Set tone controls to flat, filters and loudness turned off.
Scope both channels across load resistors. Make sure scope ground on probe doesn't short a channel.
Feed 200 Hz into an aux input, with amp connected to two 8 ohm load resistors.
Plug power cord into a kill-a-watt meter. Slowly advance level watching input wattage.
Try test with balance control, to one side only, or feed only one channel.
Then try test with 33 ohm load on one channel, 8 on the other.
_________________ de VE7ASO VE7ZSO Amateur Radio Literacy Club. May we help you read better. Steve Dow ve7aso@rac.ca
|
|
Top |
|
 |
Johnnysan
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 9:38 pm |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 16749 Location: Albuquerque, NM 87123
|
radiotechnician wrote: Set tone controls to flat, filters and loudness turned off.
Scope both channels across load resistors. Make sure scope ground on probe doesn't short a channel.
Feed 200 Hz into an aux input, with amp connected to two 8 ohm load resistors.
Plug power cord into a kill-a-watt meter. Slowly advance level watching input wattage.
Try test with balance control, to one side only, or feed only one channel.
Then try test with 33 ohm load on one channel, 8 on the other. What will this prove? Never heard of such a test for an audio amp.
|
|
Top |
|
 |
stratozen
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Sun 27, 2018 10:32 pm |
|
Joined: Apr Wed 03, 2013 2:38 pm Posts: 103
|
OK, I tried to adj the bias and the best I could get was 001.0 to 003.0, supposed to be "0" once in a while goes to -001.0 but the controls are so sensitive and like a dirty volume control but when I got it to the best I could when I turned up the volume it cut out. It took me about 10 min for each one to get to the lowest because of having to make micro adjustments and then letting it settle down. When turning adj the voltage was all over the place hitting over 100 and then settling down.
|
|
Top |
|
 |
Johnnysan
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Mon 28, 2018 12:42 am |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 16749 Location: Albuquerque, NM 87123
|
Those controls need to be cleaned or replaced.
If you cannot achieve the result expected then there is still something wrong in the circuit; your bias diodes may be at fault. They may be mounted to the heat sink (usually brown or maroon).
|
|
Top |
|
 |
joelandjoyce
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Mon 28, 2018 3:23 am |
|
Joined: Apr Thu 11, 2013 11:03 pm Posts: 664 Location: 649 Lacy Wilkerson Rd Roxboro, NC 27574
|
The protection circuit has only one relay that cuts off both channels when it detects a problem on either channel. On my SX 950 which is similar the problem of over sensitive protection tripping was due to one of the power supply negative voltages being way out of regulation. That voltage was supposed to be something like -38 or so and it had gone up to -50. The receiver worked but it tripped the protection very easily. There were a couple of cooked regulator transistors caused by bad electrolytics.
_________________ Joel Walker
|
|
Top |
|
 |
radiotechnician
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Mon 28, 2018 3:48 am |
|
Joined: Sep Thu 23, 2010 6:37 am Posts: 12437 Location: Powell River BC Canada
|
Johnnysan wrote: radiotechnician wrote: Set tone controls to flat, filters and loudness turned off.
Scope both channels across load resistors. Make sure scope ground on probe doesn't short a channel.
Feed 200 Hz into an aux input, with amp connected to two 8 ohm load resistors.
Plug power cord into a kill-a-watt meter. Slowly advance level watching input wattage.
Try test with balance control, to one side only, or feed only one channel.
Then try test with 33 ohm load on one channel, 8 on the other. What will this prove? Never heard of such a test for an audio amp. How else could you find which channel may be causing the trip without taking off the cover ? Also, the kill-a-watt is a fairly good dim bulb indicator without input voltage starvation. Ive seen lots of them incorporated into bench systems. Radio power monitoring has been possible for 70 years with the wattage eye function on signal tracers.
_________________ de VE7ASO VE7ZSO Amateur Radio Literacy Club. May we help you read better. Steve Dow ve7aso@rac.ca
|
|
Top |
|
 |
Vin Tageman
|
Post subject: Re: Pioneer sx-1050 HeadAche Posted: May Mon 28, 2018 3:53 am |
|
Joined: Aug Fri 12, 2016 1:49 am Posts: 1711 Location: Houston area, TX
|
Did you look on page 20 Fig. 16 and check for potential difference at the diff amp (Q2 & Q3)?
I see you checked DC balance, but what does your meter say for idle current? Are you able to get a stable reading?
|
|
Top |
|
 |
Who is online |
Users browsing this forum: No registered users and 5 guests |
|
|