Hi,
My old Pioneer receiver has developed an issue with its tuner after many years service. A static, crackling noise is now audible on FM only. The amp behaves perfectly on all other inputs.
The noise is very obvious on spoken word broadcasts although with the muting on there is no noise in between stations just silence until the tuner is tuned to a broadcast.
The protection circuit board required all the electrolytics replacing last year and maybe the tuner circuit board now needs the same upgrade or is there anything else to investigate first ? The part number is aws067.
Would it be simpler to change the complete tuner circuit board from a known good unit rather than all the many capacitors ?
Any advice welcome.
David.
My old Pioneer receiver has developed an issue with its tuner after many years service. A static, crackling noise is now audible on FM only. The amp behaves perfectly on all other inputs.
The noise is very obvious on spoken word broadcasts although with the muting on there is no noise in between stations just silence until the tuner is tuned to a broadcast.
The protection circuit board required all the electrolytics replacing last year and maybe the tuner circuit board now needs the same upgrade or is there anything else to investigate first ? The part number is aws067.
Would it be simpler to change the complete tuner circuit board from a known good unit rather than all the many capacitors ?
Any advice welcome.
David.
Do the center tuning meter and signal level meter work properly?
The center tune meter should be in the middle if no antenna signal is present. Does it detect a stereo signal?
Those old Pioneers are notorious for oxidized switches and could use a cleaning of the contacts in the tuning capacitor.
The center tune meter should be in the middle if no antenna signal is present. Does it detect a stereo signal?
Those old Pioneers are notorious for oxidized switches and could use a cleaning of the contacts in the tuning capacitor.
Thankyou for your reply.
The tuning meter and signal meter are working properly. The tuning meter is in the centre with no antenna connected. The amp works perfectly on all other functions it’s just the noise on FM which is a problem. It sounds like all radio broadcasts are being played from a badly scratched LP.
The amp’s switches and rotary controls were all properly cleaned 3 or 4 years ago due to a channel imbalance and scratchiness which improved things greatly. Perhaps it’s time the tuning contacts had the same treatment. Is this the same procedure using deoxit or Servisol cleaner ?
The tuning meter and signal meter are working properly. The tuning meter is in the centre with no antenna connected. The amp works perfectly on all other functions it’s just the noise on FM which is a problem. It sounds like all radio broadcasts are being played from a badly scratched LP.
The amp’s switches and rotary controls were all properly cleaned 3 or 4 years ago due to a channel imbalance and scratchiness which improved things greatly. Perhaps it’s time the tuning contacts had the same treatment. Is this the same procedure using deoxit or Servisol cleaner ?
Very possible it’s the tuning contacts. Tell tale signs are noise produced with fm muting off and as you move or rock the tuning wheel you hear all kinds of noise.
There is a well written procedure on audiokarma’s tuner section for cleaning the variable capacitor. Best to use a non-residue cleaner only on the contacts and not get any on the fins or vanes. Some have used a hypodermic needle and put a small amount of Caig fader lube on the contacts as written by a member on the fm tuner group.
Good luck
There is a well written procedure on audiokarma’s tuner section for cleaning the variable capacitor. Best to use a non-residue cleaner only on the contacts and not get any on the fins or vanes. Some have used a hypodermic needle and put a small amount of Caig fader lube on the contacts as written by a member on the fm tuner group.
Good luck
After researching Audiokarma’s correct procedure to clean the tuner contacts etc this has now been done. Although the slight scratchiness always present when fine tuning to my preferred Radio 4 at 93.4 has been eliminated the main issue persists.
Upon initial switch on today the amp behaved fine on FM for several minutes before the noise returned. I then checked the tuner board for any dry joints in operation without success.
The amp’s protection also briefly cut in after around an hour which it also did yesterday when the fm problem appeared. This hasn’t happened since replacing the caps on that board some time ago.
As the unwanted noise now appears to be temperature dependent the next option seems to be freezer aerosol as the issue is possibly being caused by further failing passive components on the tuner board. Hopefully this may isolate the reason for the fm noise but why the protection has briefly been triggered is confusing as the protection board voltages all test as expected.
Upon initial switch on today the amp behaved fine on FM for several minutes before the noise returned. I then checked the tuner board for any dry joints in operation without success.
The amp’s protection also briefly cut in after around an hour which it also did yesterday when the fm problem appeared. This hasn’t happened since replacing the caps on that board some time ago.
As the unwanted noise now appears to be temperature dependent the next option seems to be freezer aerosol as the issue is possibly being caused by further failing passive components on the tuner board. Hopefully this may isolate the reason for the fm noise but why the protection has briefly been triggered is confusing as the protection board voltages all test as expected.
sx-5580 = SX-1050
Somethings intermittant or goes noisy,
it might be because of a DC bias disturbance in the FM section causing the protection to activate.
One test is to take the Composite FM that comes out the back and feed it into a tape play input, switch to that, to monitor the Fm composite to determine if the problem exists before or after the stereo decoder section.
That muting relay has also to be known to cause problems. so test with muting off
Another problem that causes the protection to trip are c1,c2 on AWM-090(protection), we usually repklace them with 0.22uF/50V film with 5mm lead centers. But you say you changed ecaps on that pcb.
Other causes could be pre-amp, 2sa725 are known to go noisy, replace with KSA992FB, but it could be others as well, narrow down to section, see if it happens on both channels, lots of things to try out.
Somethings intermittant or goes noisy,
it might be because of a DC bias disturbance in the FM section causing the protection to activate.
One test is to take the Composite FM that comes out the back and feed it into a tape play input, switch to that, to monitor the Fm composite to determine if the problem exists before or after the stereo decoder section.
That muting relay has also to be known to cause problems. so test with muting off
Another problem that causes the protection to trip are c1,c2 on AWM-090(protection), we usually repklace them with 0.22uF/50V film with 5mm lead centers. But you say you changed ecaps on that pcb.
Other causes could be pre-amp, 2sa725 are known to go noisy, replace with KSA992FB, but it could be others as well, narrow down to section, see if it happens on both channels, lots of things to try out.
I have an SX-580 that had the same problem and cleaning the variable capacitor was my first instinct. Before resorting to cleaning/lubricating chemicals I decided to blow it out with air using a wet/dry vac in blow mode. I often dust of the PCBs this way before starting a restoration. The SX-580 tuner hasn't crackled since. It's been about 3 years now. I haven't restored this one yet. It's a daily driver that works well enough for now and it has all of it's 1979 electrolyics.
Thanks for your input Retrofier, it’s good your 580’s issue was easily sorted, the SX 50/80 receivers are well worth maintaining. Before beginning chemical cleaning a hair dryer on cold setting was used to remove the dust etc from the tuner gangs but unfortunately without improvement.
Switched the amp on from cold today and again it sounded great on FM for around 10 minutes warming through then the snap, crackle & pop began. I’m awaiting delivery of freezer spray to isolate the failing component/s.
Hopefully progress can be made in the next day or so and a repair can be attempted. After necessary replacement of the protection board electrolytics it’s possible there are failing caps on the tuner board or possibly a transistor, but I’ve been wrong before 🙂
Switched the amp on from cold today and again it sounded great on FM for around 10 minutes warming through then the snap, crackle & pop began. I’m awaiting delivery of freezer spray to isolate the failing component/s.
Hopefully progress can be made in the next day or so and a repair can be attempted. After necessary replacement of the protection board electrolytics it’s possible there are failing caps on the tuner board or possibly a transistor, but I’ve been wrong before 🙂
Spent some time over the weekend further investigating the problem with the aid of freezer spray.
Once the snap, crackle & pop began I tried very localised application of freezer spray on the caps and transistors on the FM board which made no difference. However, after cooling the transistors on the protection board the noise disappeared and the amp is now working fine with no noise issue or the protection briefly kicking in.
Is it possible that one or more of the 6 transistors on the protection is breaking down and emitting rf noise which is being picked up by the fm tuner section that is sat right next to the protection board ?
I understand from research that Q6 & Q7 are known to become weak and cause the amp to trip into protection. This theory is possible as after changing all the electrolytics some time ago, following regular amp tripping off, that problem went away but was this down to the new caps covering up the weakening transistors ?
Guess the only way to confirm the protection board transistors are at fault is to change them all which I’m able to do as they were bought at the same time as the caps. But confirmation a failing transistor on the protection board is possibly causing the fm interference would be appreciated.
Once the snap, crackle & pop began I tried very localised application of freezer spray on the caps and transistors on the FM board which made no difference. However, after cooling the transistors on the protection board the noise disappeared and the amp is now working fine with no noise issue or the protection briefly kicking in.
Is it possible that one or more of the 6 transistors on the protection is breaking down and emitting rf noise which is being picked up by the fm tuner section that is sat right next to the protection board ?
I understand from research that Q6 & Q7 are known to become weak and cause the amp to trip into protection. This theory is possible as after changing all the electrolytics some time ago, following regular amp tripping off, that problem went away but was this down to the new caps covering up the weakening transistors ?
Guess the only way to confirm the protection board transistors are at fault is to change them all which I’m able to do as they were bought at the same time as the caps. But confirmation a failing transistor on the protection board is possibly causing the fm interference would be appreciated.
No the transistors in the protection circuit would not be creating RF noise in the FM band.
Do the fm composite test? It will test your rf noise theory.
Hey thanks for your fast reply.
Not exactly sure what connect composite fm to tape playback means ? Do you mean the single rca on the back labelled fm set 4 channel being connected to tape 1 input ?
Not wishing to contradict your obvious knowledge and appreciate you taking time to respond, but the amps been switched on for most of today and the noise on fm reappeared after an hour or so and further application of the freezer spray to Q3 instantly kills the noise for a further hour or so. Freezing any of the other transistors does not have any effect.
Not exactly sure what connect composite fm to tape playback means ? Do you mean the single rca on the back labelled fm set 4 channel being connected to tape 1 input ?
Not wishing to contradict your obvious knowledge and appreciate you taking time to respond, but the amps been switched on for most of today and the noise on fm reappeared after an hour or so and further application of the freezer spray to Q3 instantly kills the noise for a further hour or so. Freezing any of the other transistors does not have any effect.
Yes. using FM mono as your source, tape monitor #1 or #2 play input, push down the toggle to select the input that is used.
Its mono so you can try only one input at a time unless you use a splitter.
You did not say if the noise was comming from one or both channels?
If your theory of "RF FM radiated noise" is true. Then try using another FM tuner/radio to see if it gets affected at the same time?
Follow up.
After being convinced the issues were being caused by the protection board it was decided that a replacement would be installed.
A known working board was sourced from Jerry at Oak Tree Vintage in the US at a not unreasonable price inc’ expedited shipping and fitted several weeks ago.
The Pioneer has worked flawlessly since with no fm interference or going into protection. The time it now takes to switch the speakers on is around 5 or 6 seconds against the original boards 2 or 3. The sound also seems more detailed and it’s now unnecessary to rotate the balance control 15 degrees anti-clockwise to centre the stereo image.
It’s good to have the amp back in full health and can only assume a component on the protection board was causing the issues although all caps and transistors were changed. Maybe the relay ?
Hopefully the problem is now sorted and the amp can be enjoyed. Whilst on the bench the bias was checked too and found to be within 10% of factory spec which is impressive after 48 years. It’s a lovely, rich and powerful beast which has outperformed many modern offerings 🙂.
Thanks for responses.
David.
After being convinced the issues were being caused by the protection board it was decided that a replacement would be installed.
A known working board was sourced from Jerry at Oak Tree Vintage in the US at a not unreasonable price inc’ expedited shipping and fitted several weeks ago.
The Pioneer has worked flawlessly since with no fm interference or going into protection. The time it now takes to switch the speakers on is around 5 or 6 seconds against the original boards 2 or 3. The sound also seems more detailed and it’s now unnecessary to rotate the balance control 15 degrees anti-clockwise to centre the stereo image.
It’s good to have the amp back in full health and can only assume a component on the protection board was causing the issues although all caps and transistors were changed. Maybe the relay ?
Hopefully the problem is now sorted and the amp can be enjoyed. Whilst on the bench the bias was checked too and found to be within 10% of factory spec which is impressive after 48 years. It’s a lovely, rich and powerful beast which has outperformed many modern offerings 🙂.
Thanks for responses.
David.
The protection board has no effect on the power amplfier unless... something is so wrong that it's affecting one of the voltage regulators but this isn't likely. The relay contacts however can cause some serious problems with the sound. I have measured distortion from oxidation causing some serious non-linear resistance on the contacts. I have also seen this clear out with use, and the units with the problem were sitting around for decades. It's kind of a quirky problem with some output relays. None of my amplifiers that see frequent use have this problem. I have only seen it when starting a restoration on something that's been in a barn for years or something similar.
I replaced the small Electrolytics around the stereo chip with ceramic of similar value. Cleaned tuner variable capacitor.
No more crackling on sx780 FM tuner.q
No more crackling on sx780 FM tuner.q