Sony HCD-MG510AV 60 cd receiver w/surround and A/V jacks - WONT TURN ON

If the fuses are really good, this is a bad sign, given what you have said about using the 12 to 120 converter. Possibly a bad power transformer. With the receiver unplugged, use your DMM to measure resistance (ohms) at the AC switched outlet on the rear panel. This outlet directly parallels the main transformer primary. If the transformer primary is OK, and there are no blown fuses or other open circuit, then the resistance should be very low, probably less than 1 ohm, since it is a large transformer. If it's in the

100 ohm range or greater, you are measuring only the primary of the standby transformer, and the main transformer may be bad. Possibly a thermal fuse opened inside the transformer.

Mark Z.

Hi Mark - there is no switched outlet in the back of the stereo. It has the main plug hard-wired in and various jacks for speakers and what not, but no other place for any AC plug to go into. This is one of the "mini-stereos" with the CD player, cassettes, etc, all in one self contained unit.

I do currently have the main cover off and notice when you plug it in, it makes the "normal" click after a couple of seconds (at least I think that is normal), and one of the belt drives on a cassette motor jogs forward for a split second. After that, the light to the main power button LED is lit red, but the power to the system will not come on. With that said, what else do you recommend? Thanks - John

If it seems to turn on normally, with the speaker relay coming on after the usual delay, and just no display, there is a chance that only the -30 volt line for the display is down (or some other section of the power supply). There is a 100 ohm fusible resistor on the power board, R901, near the large connector which goes to the main board. This resistor could be bad.

There is also a separate fuse board, and there could be bad fuses there - don't recall if you said you had checked those.

Mark Z.

I actually checked the "hidden" fuses on the power supply board above the transformer a while back. I went ahead and removed the power supply from the stereo again tonight, removed the fuses again and they checked ok for continuity. I then checked the resistors on the board and they seemed to check within tolerance - one of these was the R901 you speak of. I went ahead and checked the switching diodes (they seemed ok) and the two 1N002 diodes. One of the 1N002's (D902) tested kind of odd so I pulled one leg out and it checks out the way it should. When I put it back in the board it cheked out the same as before across the ends - ".051" and it didn't matter which way I had the black and red leads of my DMM. As you probably already know these should ideally check between .4 - .6 one way and "OL" the other. So I am not sure why this diode is reading this way, but I did notice one of the traces is going to a small transistor Q901, but I do not recognize this as one I know how to check/ meter out The numbers on it are C107 (top line) and M131 (bottom line). On the same trace going the other way it leads to an OMRON 5VDC black box (not sure if its function). Does this diode reading sound suspicious or like soemthing else on the board is causing this goofy reading? Considering I pulled one leg out and it read ok I beleive the diode to be good. Other than this, I don't readily see anything that looks out of the ordinary. Any other ideas for me to try? I will leave the power supply on my bench overnight. Thanks for your help this far. John

Oh and as far as it turning on normally, I am not sure if I am misleading you or not. The thing doesn't turn on. When you press the power button it doesn't do jack. When you plug it in though it does put power to the power button LED and it looks like there is fire going to the cassette motor too as it lunges forward a bit. But that's all she does other than make the click after plugging it in, but I don't know what that click means - just seems like it always did that. John

Well, sorry we got off track. These models can be tough sometimes (well, most of the time it seems).

Generally speaking - one must confirm the standby status first. The DC voltage derived from the standby transformer, usually 5 volts. The reset line to the microprocessor should rise smoothly and pretty quick from 0 to 5 volts when the power cord is inserted. The crystal should be running. If no scope is available, the DC voltage on the crystal should be about 1/2 of the

5 volts. There would be a relay turn-on line from the micro which obviously should fire when you press the power button.

I'm concerned about that relay firing when you plug it in, though - doesn't sound right to me.

Although your model is somewhat different, there is a history I should make you aware of.

On the HCD-GX450 and 250 models there was an issue with the flat cable which connected the main board on the side with the front panel. Somehow even though these were new units, sometimes there were bad or intermittent connections where this cable plugged in, both at the main board and at the front panel side. Caused a variety of unusual symptoms INCLUDING one I saw where the relay fired upon plugging in, but would not turn on.

Sound familiar?

Mark Z.

Mark - It may take me a day or two to digest your last post - it's pretty deep for me. I will actually be traveling the next couple of days for work so it may be a while before I can look into what you posted. I should be able to reply by the coming weekend. Thanks - John

You can e-mail me direct at:

snipped-for-privacy@labolgcbs.net

and reverse the domain name.

Mark Z.