Sony STR-DH820 not powering up

[the loner]

I have purchased this AV amp, (along with 3 others, but I want to work on 1 maybe 2 at a time) from an auction for cheap, $40 for 4 of them.
When I plug in the amp, I can hear the relay click on to energize it(it is a Tyco Electronics SDT-S-105DMR2).
If I unplug and re plug it back in, after about 20 or so times, it will power on .
When it does power on, I get sound from the 2 speakers that I connected to it, I haven't plugged in all 7 speakers in because I'm trying to get it to work.

I have a feeling that it maybe the relay being weak, or maybe a cap that is dying, but I don't know how to test it to correctly find the problem.

These are my voltage readings.
From the power plug
71.7 V hot (black)
25.2 V common (white)
Fuse 71.4V both sides
Relay has 5.2V from under side
First picture.

I could be wrong, but the transformer looks burnt, but that maybe the from the welding (second picture)

DCDC power supply voltages (third picture) are as follows...
starting from left plug pin 1 working to the right
14.53v,
n/c,
0v,
0v,
0v,
6.3v

right plug pin 12 working to the right
6.3v,
0v,
3.95v,
3.95v,
n/c,
6.3v,
6.3v,
0v,
0v,
3.9v,
n/c,
3.9v

The next 6 pictures are what looks like fluid/water damage which I'm not to worried about, I have cleaned up the board but if I can get it working properly, then I will put all boards into my ultrasonic cleaner.

The last picture is the bottom of the power supply.

I know that you don't really do amplifiers, but any help would be greatly appreciated.

Thanks.

[budm]

Re: Sony STR-DH820 not powering up

I cannot find the service manual for this model, but from the look of the first picture which has the small transformer and relay on it, that should be the standby power supply to run the main board, when the receiver the turn on command from the remote or the power switch, the main board will then send the signal to turn the big power transformer through the relay contact. So if the relay contact is bypassed, then you should see 120V on the primary winding of that big transformer.
By the way, when you measure the AC in the primary side, you do not use the safety/chassis ground as the ref point, that is why you are reading 71V on the Hot (black), you will put the AC probe on the Hot and Neutral to see the AC input voltage feeding the transformers.

[the loner]

Re: Sony STR-DH820 not powering up

Thanks budm. I do get 115.9v when connected properly as you stated.
I have the service manual also.
I just don't know what to check as the amp will turn on after about 20 un plugs and re plugs to get it to come on, it's a guessing game and the luck of the draw when it comes on.
When it does work and I shut it off, then try to turn it back on again, I go through the same process of un plugging and re plugging it in.

[rhomanski]

Re: Sony STR-DH820 not powering up

Sounds like the contacts in the relay. Either open it up and clean them or replace the relay.

[ben7]

Re: Sony STR-DH820 not powering up

I wonder if it is one of those "energy saving", "switching" standby power supplies.

Like this one from the EEVblog: http://www.youtube.com/watch?v=MwvjAtSr5t8

[the loner]

Re: Sony STR-DH820 not powering up

Thanks rhomanski, the relay is the problem. I sanded the contacts and it works a lot better, I just need it to work 100% as it will be given to my father in law as a present.
I just need to source out a relay now.
If I can't find a direct replacement relay, can I use one of these as a substitute...
SDT-S-105LMR2,000 5VDC Sensitive 150mW coil 8-1419125-3 or
SDT-S-105DMR,000 5VDC standard coil 8-1419125-0 or
SDT-S-105LMR,000 5VDC Sensitive new design AgSnO2 1 form A (NO) 250mW 8-1419125-1
Either I'm not looking in the right place or I can't seem find exactly what I'm looking for.
And I don't need 500+ minimum quantity, just 1

[the loner]

Re: Sony STR-DH820 not powering up

I hope that I don't get into any trouble posting the relay data sheet but here it is...

[budm]

Re: Sony STR-DH820 not powering up

So what is the original relay P/N as printed on the body? SPST (Single Pole Single Throw) type? Or it is the one you post the PDF spec ?

[the loner]

Re: Sony STR-DH820 not powering up

The original relay # is SDT-S-105DMR2. I put the pdf sheet there for everyone's reference if they would like to see it to compare.

5V Rated voltage VDC,
3.75 Operate voltage,
0.5v release voltage,
100 ohm resistance +- 10%
250 mW Rated coil power.

I have read the coil resistance and rated coil power are different, but I don't know if it will cause any damage if I use a different value, because it is working nicely right now.

[budm]

Re: Sony STR-DH820 not powering up

It is relay with 5V DC coil voltage, the coil has 100 Ohms reistance and consumes 250 mili-watt. To improve the reliability is to find the one that has the contacts that can handle high inrush current, that big transformer and the large filter caps will draw lots of current when the power is first applied.

[rhomanski]

Re: Sony STR-DH820 not powering up

The original relay is rated at 10 amps. Should be just fine. This place sells a similar one. http://www.onlinecomponents.com/te-c...tml?p=12114038 . I would try for an original replacement part. If the pins line up I would just use it.

It does have a slightly lower coil resistance which may cause the transistor that runs it to get hotter. Just monitor the temp for a while when you first install it. If you have to put a bigger transistor in.

[the loner]

Re: Sony STR-DH820 not powering up

So if I understand correctly, this relay, SDT-S-105DMR,000 5VDC standard coil
(part #8-1419125-0) is fine, since the voltage is the same, it has less coil resistance
(46.3 ohms vs 100 ohms) , and it can handle more current (540 mW vs 250 mW)

[the loner]

Re: Sony STR-DH820 not powering up

All 3 relay's are physically the same, as in pin layout and dimension, just the internals are different, as in current draw, and resistance.
SDT-S-105LMR2,000 5VDC Sensitive 150mW coil 8-1419125-3 or
SDT-S-105DMR,000 5VDC standard coil 8-1419125-0 or
SDT-S-105LMR,000 5VDC Sensitive new design AgSnO2 1 form A (NO) 250mW 8-1419125-1

I'm not sure what the coil type means on the last page of the pdf file stands for though.

[the loner]

Re: Sony STR-DH820 not powering up

I did see that website, but I wasn't sure if the specifications were ok to use that relay.

http://www.onlinecomponents.com/te-c...tml?p=12114038

[budm]

Re: Sony STR-DH820 not powering up

"it has less coil resistance
(46.3 ohms vs 100 ohms) , and it can handle more current (540 mW vs 250 mW)" The lower coil resistance will cause more current draw by the transistor to be higher, that is why rhomanski suggested to check the temp of the transistor that drivea this relay coil, since the resistance is half the original, the current will be twice as much through the transistor which can cause the transistor to heat up, it not relay current handling specification, there is current handling spec for the relay contacts current spec, which is 10A.
Bottom line is that the sub relay consumes twice as much power as original, so if the transistor that drive this relay can handle it, then there will be no problem, if not, the transistor can be damaged.

[rhomanski]

Re: Sony STR-DH820 not powering up

This one http://www.mouser.com/ProductDetail/...p1G2fZFP9mw%3d is the best electrical fit but will not fit your holes. If you turn it upside down and run wires from it's contacts, what we call dead bugging, you shouldn't have to worry about anything else. Just glue it upside down somewhere on the board as close to the original spot as you can. I've used RTV in the past. The form a gasket for your car. It holds forever but won't dry out so it can be removed pretty easily. I have always made sure to keep it away from all contacts because I'm not sure if it is conductive. It could short something out if it isn't used properly. I don't think it would but I've never tried it, so I can't say for sure.

[rhomanski]

Re: Sony STR-DH820 not powering up

To explain a little better. Your relay is probably used to control the power to at least parts of the unit. This means you don't have full currant flowing through switches and such as that. Since the unit probably has a remote control, it will be run by a transistor. In the old units I work on the relays are to delay start up to control the currant draw in the first second it's turned on. Also they are used to protect the speakers, when the power supply voltages are all correct, the relay closes and connects the speakers. That keeps you from putting DC voltage on the speakers in a malfunction.

The transistor supplies all the currant for the coil, it has to be large enough to to do it without overheating. If the coil draws 250 mW's then the transistor has to be able to put out more than that. Engineers almost always leave a little fudge room. If they run it close to it's maximum output they usually put a heat sink on it. This helps it dissipate the heat generated by that much currant flow. What I meant in my other post is that with less coil resistance, the relay might draw more currant and overheat the transistor. It can be replaced with a bigger transistor or it could be fitted with a heat sink. Another possible solution would be to mount a small resister in series with the coil to bring the resistance up to what the transistor is designed for. If the relay still actuated then no problem.

One thing engineers discovered in the mid seventies when they started doing this, is that when the relay is deenergized, the collapsing magnetic field will induce a voltage in the opposite direction. This reverse voltage will ultimately break down the P N junction and kill the transistor. They began putting in diodes in the path so currant would flow normally but the reverse voltage would be stopped by the diode. The diode gets damaged just like the transistor would, but it has a larger P N junction and will last longer. I hope that clears up some things.

It would probably be easiest to just dead bug the relay I pointed out. The other things I spoke of could work, but might not be easy or as reliable as you want.

[budm]

Re: Sony STR-DH820 not powering up

From the way it looks, that relay is used for supplying the 120V to the primary side of the large power transformer for the audio power amp section, picture #2 on post 1, this is very common setup for the receiver, that is why I suggested higher inrush current rating of the relay contact, the inrush current can be as high as 10 time the running current. Most relay company will post the inrush current rating of their relay. There are other relays for speakers protection as well.

[the loner]

Re: Sony STR-DH820 not powering up

Sorry for not getting back sooner to everyone, it's been a busy week. Reinstalling windows 7, helping a friend move.

I plan to order that relay this week and try the "dead bugging" you mentioned rhomanski.
Not sure if there are any other Canadians in this posting (it doesn't look like it), but Digikey also has the relay that you mentioned rhomanski,
http://www.digikey.ca/product-search...Q305&x=18&y=13

I do appreciate the help everyone has given me though.

There is way too much to learn but I can slowly learn from other members. I like to think about ways I can fix electronics and I don't expect to be spoon fed, but when I don't understand, or I don't feel safe, especially with high voltage transformers, I ask questions.

baman, the receiver was purchased from an auction, so there is no warranty on it at all.