The radio was bought with no audio, i got the audio back on by replacing an opamp on the audio board & a zener diode that had burnt out but the fault now is faint & distorted audio on am ie sw & air band the later being the worst
Hi I was the one who had the the Satellite 750 with the no audio fault I have borrowed a friends Radio to find out what had been burnt out,I found out it was a low dropout regulator that feeds a opamp it should supply 4 volts ,I have found out that the only known company who has these in stock is Mouser Electronics in Germany & they wont supply to England so i have ordered a variable voltage regulator pre built off ebay so I will link this with wires onto the Audio board,This radio has been working for a few months with a resistor feeding the op amp with 4 volts but the audio is a bit distorted at high volumes, the regulator should help I hope.
Testimonial: "You did not say what you did but i think you mean a reset which i have already done,the problem with these sets is the lack of circuit diagrams thank you for taking the time to post a reply it might help someone who has a processor lock up many thanks again."
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The SW FET preamp transistor, Q1, on the underside of the circuit board blows if a static electric discharge hits the whip antenna. In my case, a cat rubbing against me & the radio on a very dry winter day did it in. The back & circuit board has to be removed to get at it. The micro transistor & the solder connection are very tiny, so hard to replace. The antenna jack should still work, because the preamp is only for the whip antenna's SW reception. An easier solution would be to just run a wire from the antenna jack to the whip antenna, but you would no longer have the whip's preamp benefits, or just use a longwire antenna connected to the jack for SW. Also beware plugging into the jack disables the AM ferrite antenna inside, so you might not want anything plugged into it for AM reception because the internal ferrite seems to perform better than any external antenna.
I dont know what all modifications you have done but here are some tweaks that would be good:
IMO the tweak steps that should be made and order I suggest is good would be following
1) eliminate the output electrolytic caps from analog output (C656, C658, C655, C657)
I have replaced them with wire jumpers. It would be wise to check the
DC component at output connector with multimeter. In my experience it's
never more than abou +/- 20mV, which is mostly of no concern. Only if
you have a true direct coupled amp where there are no caps in signal
line it might happen that the DC component will also be amplified and
sent to speakers. I think there is no commercial amp built this way,
but some DIY projects might be.
2) Change the opamps. National LM6172 seems to be the most popular candidate and is the one I'm using.
Here the most important is to make sure you will place the additional
decoupling caps to the supplies of opamp as close to pins as possible.
I have 0.1uF polyprop caps from pins 4 and 8 to ground. When choosing
the caps go for the ones that have as small dimensions as possible and
as short legs as possible. Also place a cap on top of the opamp between
+/- pins (pins 4 and 8). The value of this cap is not critical. Here
you should pick some sort of SMD cap with as big capacitance as
possible. I used some that were soldered off of some scrapped Intel PC
motherboards. It is (at least I think so) non polar cap and the DMM
measured it 20uF !!! I don't know if its right but it fits well on top
of SMD opamps (I didn't get DIP cases from RS for some reason, even
though the part nr. was right). A good place to look for ideas about
opamps and decoupling is audioasylum forum.
3)Modify the clock. Install a sepparate one or use the description on
acoutica.org site. I did my clock mod very sililar to that
independently and as it turns out the techical solutions were similar
and also our findings about changes in sound...
4)Better decoupling to supply lines. Use your imagination here.... One
warning though, I once decided to change almost all the el. caps in the
player for better ones (Nichicon xx, I don't remember the series at the
moment). So, I replaced them and to some places I just put bigger
values than stock. Well as it turned out I managed to overtweak a bit
and now it takes about 30 sec before the display lights up :) I have
studied it a bit, also with scope but can't fiqure out what causes the
delay. Player starts normally and other than that there is no
problem... so I have accepted it as just one more little thing that
makes my player special.
The bad news is it could be any of them. or it could be the lighting- CFL's and regular flourescent lighting are bad for audio, as are switching supplies used in TV's, microwave ovens and some musical gear. They are worse than lighting dimmers for noise.
The thing to do is start at the speaker itself and work through the chain of devices to find the one distorting. An old transistor radio is useful here. Most actually do have enough power to faintly drive a large speaker- listen for scraping and rattling- it would mean the voice coil windings may have come loose or the coil form is damaged from heat.
Move back to the amp input and try again- this time listen for a clipped sound if the speaker checked out okay. It would sound like the Charlie Brown adults in the cartoons. That would be a failure of an active component in the amp. If you now hear rattling or scraping- the speaker voice coil is bad and should be repaired or replaced.
If it sounds good, move back to each deck. apply your radio- volume turned down to an input it one is provided. Each should sound clean like the amp did. If no sound or distorted sound is found here- which is the most probable location, it is likely one of the IC chips is at fault. Likely a 4558 if an IC fault, otherwise suspect dirt or hair on the encoder connected to the spin platters.
I left mine under my bed for 2 years, when I turned it on it sounded very distorted. I took it apart and found the speaker to be faulty, I suspect my under floor heating may have had something to do with it. The internet suggests it's a fairly common problem. People seem to agree a sony 7600 speaker is the best replacment.
All inputs are switched and go through a series of amplification stages. If the volume appears to change correctly, but hte sound is just distorted independent of the voluem, then the problem is likely to be in the beginning stages of the amp. This can be as simple as a defective OpAmp IC or diff-amp section or even a voltage regulator failure. Without the exact model number and some internal measurements, I can not say for sure. Can you supply more details?
the ddt circuit on this amp is goofy, they use a 4060 opamp with the inputs at -14 to -15V, the spec range is only +/-12V. So it is possible for it to nuisance trip. There is a button on the back to disable the ddt, try that. I've alos had luck replaceing the 4060 with an LM358 whose input spec is not violated in this application
Distortion comes from the audio signal being clipped by one of your elements in the system.
What I would do first is measure the output of the radio with an oscilloscope to see if the signal is good. If it is then I would determine if the source of the distortion is the amplifiers or the speakers.
If it is the radio have that fixed or changed, If it it not, it might be a case of the radio overdriving the Amps causing them to clip the signal peaks. check for the max signal input of the amps and make sure the system is adjusted for that.