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Hi,
I have a Pioneer sx-727. I'm the original owner over 40 years.
Recently developed fm problem.
Crackling sound on fm station and then station drifts. No noise at all between stations.
AM reception also not good, background buzz, humm between
stations on AM only. Unit works perfectly with CD and other inputs.
Any ideas what my problem might be? This all started a couple of weeks ago,
when I noticed that signal strength meter was not illuminated, I assumed just bulb burned out.
Tuning center meter still works. Any help would be appreciated. Thanks.
Follow Ups:
Solder all wire wraps. Time to replace all electrolytics. If still does not work, the tuner requires lab equipment to repair & align. You will have to hire a tech.
As for electroyltics, use CDE 380DX for the main PS filters & if you cannot trace the audio caps, just replace the rest of smaller caps outside of the power supply board with Elna Silmic II. The Elna are pennies each from DigiKey and outperform the expensive Black Gate anyways that are not being manufactured any longer.
I did the op-amp & capacitor upgrade to a Philips 7851 & the receiver sounds way better than anyone with reason will believe- until they hear it.
You should recap it. If its the same as a SX-737 there are also a lot of wire wrap terminals in that receiver. Oxidation can play a major part in failure in these receivers. If you are going to do the recapping yourself you should consider soldering those wire wrap terminals.
Minor build up of oxidation on the wire wrap terminals seems like a small issue but if you consider the number of wire wrap connections, the oxidation is a big player in failure in these units.
I have a SX-737 that still works but the tuner is also not what it should be and the PS caps are starting to leak. I am certain that the electrolytics in my SX-737 are out of tolerance or on the point of failure. I have the unit on a shelf awaiting recapping and soldering of the wire wrap connections.
Your SX-727 is older than my SX-737 and should need recapping. Following the recapping and fixing the wire wrap connections you will then have to have the tuner aligned.
Sorry there isn't any good news here,
Ed
We don't shush around here!
Life is analog...digital is just samples thereof
I've had a number of Pioneers that drifted.
The bottom line is worn out wraps, caps and coils. But the real bottom line is it is going to need equipment that most people either don't have or don't know how to use properly.
If the IC failed you would not get FM in. Drifting is a component failure or corrosion in a coil. So if you can check the MHZ cominig out of those coils - go to it.
charles
While it might be a small issue in something like the power supply, the level of resistance due to oxidation could cause BIG problems in a tuner's RF stages.
You've given him great advice, Ed! Re-cap, and clean and solder those wire wrap connections.
No kidding it needs to be repaired! I hoping to get some suggestions on
where the problem might be, or how to diagnose it. I have schematics,
and can replace components.
You have one two issues or both going on..What you have in this unit is a muting and filter IC for the multiplex as well as the AM audio signal that may get processed thru the same IC..The other issue would be the power supply source that feeds that IC and chances are the DC voltage could be low or have lots of ripple on it due to bad filter caps in the power supply.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
Mikey,
Doesn't the SX727 use ua741 IC's in the IF strip. If so they were often problematic back in the day with just the symptoms the OP listed. That said the capacitors and wire wraps as per Ed's suggestion above would have to be taken cars of first.
Gerry
Thats the one...You hit it exactly..Hopefully its just the filters feeding because that IC is no longer in production.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
Thanks for the info.
I'm going to look at the AWR-011 Power supply unit board.
I'll check the voltages, they should be
pin 2,5,6,7 12.5v, 30v, 30v, 36v
Sound reasonable?
Yes
That's correct but it's important to note that even if the voltages are correct,you still can have ripple feeding that IC in the multiplex and therefore you need to change those power supply caps for the source that feeds the IC in question.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
Anyone know what the tolerance should be on these voltages.
For the AWR-011, Power Supply unit board
the schematic says
pin 2,5,6,7 12.5v, 30v, 30v, 36v
I'm measuring
pin 2,5,6,7 10.5v, 27.5v, 27.5v, 33v
Is this within tolerance?
Also anyone know what the output of the big transformer (ATT-050)should be
Nothing listed on the schematics.
I'm measuring
pins 13, 12, 10, 3 26vAC, 25.5vAC, 35v AC, 0 (AWR-011 board).
Numerouno
Chuck is correct in that you are in the normal 10% range however,for that receiver, I would say you are low being all the sources are reading below published spec..You need a recap and I can almost bank on it..If I put on a scope on your amp with a signal going thru it,i will see audio riding all over that power supply.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
You're in range. ALways give it about 10% for age and part tolerances.charles
PS if you feel a need to have a snotty reply - find another site to do it on.
Edits: 02/11/12
If you are getting drift then at the least you are going to need an alignment. But it sounds like you need it repaired anyway. Tuners are kind of a specialty in repair work.
charles
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