Sony str-k502p Amp quiet channel.

[NxB]

I have an STR-K502P amp that I got for free. The left channel seems to be quieter than all of the others. I don't have the AV System remote so I can't individually set the channel volume. Thing is I already did a full reset. Any idea of what it could be. If an IC was dead I figure it would go into protect.

I'm planning on borrowing a laptop with irda and trying to use LIRC to emulate the RM-U305 remote I need. I have a feeling something is broken though, any thoughts or experiences with similar models?

[Krankshaft]

Re: Sony str-k502p Amp quiet channel.

There is a chance that the system saves those settings in an EEPROM if they don't go away after unplugging.

It all depends on whether the reset resets all of the EEPROM values if not then yes an IR emulator would be a good bet to check the volume level of that channel.

Give that a shot first and if that doesn't work post back.

[Toasty]

Re: Sony str-k502p Amp quiet channel.

Plug headphones in, see if quiet problem remains on channel.

Surround system typically doesn't have any control for L-R balance or F-R fader. It is set to distances from listener according to Sony manual. Remote just duplicates front panel. Make sure speakers are polarized correctly and react properly to input. Use 1 or more C or D battery to test.



Toast

[NxB]

Re: Sony str-k502p Amp quiet channel.

Remote lets you change individual channel volume according to the manual. The 2 functions I need are on the remote, test tone and vol+ (not master). Different speakers do the same thing so its not just the 1 speaker. Balance is adjustable from the menu on the unit. When I adjust it all the way to one side, its still quiet. I'll try doing the same thing with headphones.

[Toasty]

Re: Sony str-k502p Amp quiet channel.

Yeah, my bad. Not used to setting that on a surround system. Page 33 says you can set individual levels from unit, no need for remote.

Is this loss all on one side?

[NxB]

Re: Sony str-k502p Amp quiet channel.

Headphones work fine. Balance setting does nothing for them. It seems like there is something up with the balance. You have to move it all the way to R to get the L and R to be relatively the same level. If you put it to L all the way you get no sound from the right speaker. If you put it to R all the way you still get sound from L.

Level menu has no volumes for L and R but the remote has 2 volume controls. Even after re-reading the manual I'm not sure if I can change the volume with it or not.

Anyways,

I'm guessing something is up with the outputs. What should I look for, since everything at least partially works.

[NxB]

Re: Sony str-k502p Amp quiet channel.

I looked inside and some ICs are disconnected. It doesnt look like they are shorted out... hmm.

[NxB]

Re: Sony str-k502p Amp quiet channel.

Resoldered ICs, not much changed. The NEC PC2581V get fairly hot, almost too hot.

[Toasty]

Re: Sony str-k502p Amp quiet channel.

Nice blurry picture... lol Glasses just make it crystal clear that it's blurry...

>>I looked inside and some ICs are disconnected...<<
Oh Joy! Somebody's f**ked with it before! See if any parts appear missing. Service manual is out there for $4 or so. WOW! 44 pages -

http://www.e-servicemanuals.com/prod...d_id=954645026
**NOTE - NOT an endorsement of that site. I just found it on Google.

Here's the part you mentioned. If it's getting hot, without volume being turned up, it's very suspect. Just make sure speakers are always connected when on. Or at least a proper resistive load.

http://www.bdent.com/search/part.jsp?partnum=UPC2581V
Be wary of fakes. Wizard sent me to this site for my Panasonic parts because of fakes.

Toast

[Krankshaft]

Re: Sony str-k502p Amp quiet channel.

Most fake ICs on the market are factory rejects that didn't pass QC standards so what do they do?

Some damn assholes scoop them up and resell them to unsuspecting people.

I got conned on my first set of STK amps in 06 10 bucks each my ass.

I only order from Encompass now who gets their stock straight from Sanyo .

Modifications are never a good thing unless careful thought and understanding of the circuit are put into them.

I'm working with a guy via e-mail with a HP 1955 monitor now where the tech did some creative modifications removing components and subbing others never good . Yeah great idea remove a poly cap on one side of the circuit and leave it on another it leaves me to question whether he subbed a replaced transistor with a proper equivalent.

But I'm going on a tangent that picture is way too blurry to make out anything I don't wear glasses but even if I did they wouldn't help .

[kc8adu]

Re: Sony str-k502p Amp quiet channel.

many of these parts are lower rated parts remarked.depending on the app they may work anywhere from 5 seconds to 50 years.
ran into some stk730 like that.they were fine in the 27" rca set but would run about 5 minutes and go bang in the 36" even though they were the -120 .
talked to the supplier and we figured out that the whole lot was remarks.probably the -050 or -080 type.

[Krankshaft]

Re: Sony str-k502p Amp quiet channel.

Remarks that's NTE's entire business isn't it ?

They do that crap right in the good ol' USA too about 1 town away from me a matter of fact Bloomfield, NJ.

Popular ICs are the scammers favorites all you can do to protect yourself is order from major suppliers that have accounts and order directly from the component manufacturer.

That means staying away from fleabay and googled suppliers no matter how tempting their prices may be.

[NxB]

Re: Sony str-k502p Amp quiet channel.

Thanks for finding the ICs, I don't think anything else was changed except some mosfets on the controller board. They appear to be working. Better pictures are coming. I could only use my phone as my batteries were dead in the camera. You have to turn the volume up to 20 or 30 to get a decent level which seems wrong. I'm testing with 2 8ohm 75 watt speakers.

Don't know if I should get new drivers for the amp or if I should replace some of the output ICs. There is also a cap I'm suspicious of. Its 16V 47uf and its right by the inputs.
I don't know if the so called "service manual" is just schematics and nothing else. I might give it a shot but I don't know if its worth spending money on.



These 2 were either desoldered or the solder broke off.

[Krankshaft]

Re: Sony str-k502p Amp quiet channel.

Do you have a scope so that you can measure the amplitudes of the input before the transistor amp and after it (the output signals)?

You first must figure out whether it's a failing output transistor or a reduction in signal to the transistor amps input due to the volume control.

Inject a steady tone into it from your computer sound card I think there is a free tone generator on the Internet somewhere the name slips my mind at the moment.

The fact that a component needed to be replaced in the past doesn't give me much doubt that another component may be on it's way out.

Personally I've had more trouble with Sony products then I'd care to admit I seem to spend more time fixing them than using them. From my PS2, my two Sony TVs, and my lastest Cybershot digital camera . I eventually junked the two TVs I had to stop the monetary bleeding.

[NxB]

Re: Sony str-k502p Amp quiet channel.

No scope. I got the service manual. I should upload it here. Thing is I don't know why the 2 output Ics were disconnected and how it worked without them.

[Toasty]

Re: Sony str-k502p Amp quiet channel.

NxB >>These 2 were either desoldered or the solder broke off.<<
Solder broke off? How do you mean?

Unsoldered underneath, from circuit board do you mean? Somebody was def messing there. Make sure their tabs are not shorted to the heatsink. Ohmmeter plz.

They could be the cause of that IC being so hot. Are they connected to/from it?

NxB >>There is also a cap I'm suspicious of. Its 16V 47uf and its right by the inputs.<<
Why suspicious?

Krankshaft >>...more trouble with Sony products...<<
Yes. Very finicky products. They always seem to have 2x the number of adjustments compared to everyone else. Primary rule with Sony -NO (semiconductor) SUBS- Original parts only. Goes waaay back to early Trinitron days. Couldn't get guys to learn to stop using SK or ECG subs. Get Sony part; problem goes away and stays away.

Toast

[NxB]

Re: Sony str-k502p Amp quiet channel.

Cap is dented at the top, its in the pic. Yes, ICs were completely disconnected as if someone had used a desoldering tool on them. Every input and output still worked on the amp. I checked them for obvious shorts, like the heatsinks and nothing. I don't know if the NEC ICs got hot before I reconnected the MN and the MP, I never ran it with the cover off when first testing it.

[Toasty]

Re: Sony str-k502p Amp quiet channel.

Can't determine problem of dented cap from pic. Not really evident. Minor dent is likely not a problem. Big dent, yes, could short. Unsure? check with ESR meter if you have. If not, then check with ohmmeter or just replace it.

Pics are of transistors or IC's you said got hot? I'm unclear what MN & MP are or what that means. What IC is getting hot?

Can you post the schematic or at least the board layout so we can follow along?

Toast

[NxB]

Re: Sony str-k502p Amp quiet channel.

MN and MP are the output ICs, they start with that.
NEC PC2581V are the amp drivers, they get burn your finger hot.

Here is the service manual:

http://www.quickfilepost.com/downloa...5891b93059cb32

[Toasty]

Re: Sony str-k502p Amp quiet channel.

Sony puts out some damn fine manuals, eh?

MN2488 & MP1620 are output transistors, not IC's. Now I'm not confused.. LOL

Are they getting hot since resolder?

Both of the uPC2581V are getting hot? IC701 & IC702?

How about the other? IC501 STK350-230 ?

Toast