Sony HT amplifier/receiver repair

[onedog]

Hi
I'm interested in learning more about electronics repair using a "protect mode" receiver as a project and, at the same time, saving a bit of the planet from land-fill misuse. Disclaimer - I'm coming off a low knowledge base.

The receiver goes into protect mode (with or without speakers attached and even at low volume) after varying times but generally just after the first relay kicks in. When first noticed, the main heat sink for the 5 amplifier ICs got very hot but now I don't leave it on long enough to get hot. On a recent occasion using the remote's Test Tone, there was no output from the (front) right or the sub-woofer channels. In the photo, I have put a small black mark on the heatsink above IC751 (the R channel amplifier).

From Google, I see that this gear may be prone to poor solder joints??

My local repair guy doesn't want to know but, just maybe, there might be a simple fault/fix.

I'm always concerned not to breach etiquette in a forum such as this but if I slip up, please yell.

The User and Service manuals were too big to upload, so they can be accessed from the following DropBox link.

https://www.dropbox.com/sh/6elqb0zx30yf7eq/AAAwIdRRUTUbtb1Sy2VjJBhCa?dl=0

I'd be grateful for any pointers.

 

[davenn]

hi there
welcome and greetings from another Sydneysider

I don't see any obvious bulging caps.
You really do need to remove the boards from the case so you can get at the solder side of the boards and check for dry joints

particularly on the small PSU board and large main board

 

[onedog]

Apparently, someone has had a shot at this receiver previously.
Taking one board at a time, pics below are
1. solder-side of amp board, showing a faulty join at the FR speaker connection.
2. close-up of faulty join.
3. same area after I 'fixed' the join

I continuity-checked the area and I think I made a proper fix.

Living in hope, I re-connected but still got protect mode.

I can't see anything else obviously amiss.

 

[73's de Edd]

Sir onedog . . . . . . . (is enough)


Page 13 of your schematics SECTOR D6 is where your dastardly deed is probably being collected and routed to.

Your O/L protection circuit sensing area.

Use DVM in DC voltage function, low range to monitor the base of Q731 and just see if any unwanted voltage level presence shows up there after power up and your usual wait..

PROBABLY SO . . .then we just need to backtrack to Potted Power IC's 751-701-501-601-651 to confirm from whence it doth emanate . . .therewith.

Looks like your foil repair corrected the interconnected / crossover connection error and is now in proper order.


73's de Edd

 

[onedog]

I hear you, Sir Edd
The time difference and my golf booking will slow me down a bit.

Q731 is blocked on one side by the main heatsink and on the other by C730 but I'll try to find an equiv point to monitor (after I find my magnifying glass).

Thanks for your direction.

 

[73's de Edd]

Sir onedog . . .

Well the bad news is that Drop Box has already dropped your Sunny schematic / manual..
But the good news was that I was able to glean that info at that time, direct from the schematic.
Since Drop Box wanted the additional hassle of signing up, in order to be able to download the full manual.
So I therefore didn't get and now have the FULL model number identification of that Sony Home Theater unit.
Respond to my accompanying "conversation" message; to then initiate an E-mail exchange of the manual.
I do believe that my " Clouds" 100 terabytes can then fully accommodate it.
There must be about 4-6 laterally conjunct circuit trails that also co-join with that connection that I referenced.

73's de Edd

 

[onedog]

Sir Edd

My bad on the DropBox - over-enthusiastic cleanup. Manuals now re-instated at:

https://www.dropbox.com/sh/v5ejz7h85h5xs4b/AADaxuB2KIKVXhMNJgj45QM7a?dl=0


As you suggested,

no speakers connected,
black probe on chassis,
DVM set to 200mV,
red probe to base of Q730 (same as Q731),
reading when in protect mode -8.1
​

How am I doing?

 

[onedog]

I have just about reached my limits here. Given the earlier indication of a problem with the FR channel, I expected to find a cause somewhere around IC751. Instead, with protect mode engaged, no input and no speakers, I detected almost B- voltage on pin1 of both IC601 and IC701. The other 3 channels had 0 volts on pin 1.

Any suggestions gratefully received.

 

[73's de Edd]

Sir onedog . . .

Why 'soitanly . . .as per the suggestions .

You said above :

DVM set to 200mV,
red probe to base of Q730 (same as Q731),
reading when in protect mode -8.1

Now to me that reads as -8.1 mv . . .considering you being on the 200 mv range.
Thereby that would be no problem.

THEN the statement :

I detected almost full B- voltage on pin1 of both IC601 and IC701

Would be indicative of a serious problem, internally of those two I.C.'s
Since pin 1 is an input and it should be Zero volts unless resistors R602 and R702 , respectively are letting that voltage in.
Otherwise that pin is being capacitively isolated from DC entry ..
You can see that the DC power input pins are PIN 5 for the +28 and PIN 3 for the -28.
and our usual concern is that the IC's internal circuitry balances out and leaves close to 0 volts at amp output pin 4.

Considering that IC's IC 602 and IC 702 are bad . . . . .

Suggestion:

You then should still have 3 good units out of the 5.

Choose one of the good ones . . .and one of the bad ones,Take out the heat-sink mount screw on each unit
and then use a knife blade's edge to ever so gently lever the IC's heatsink plate away from the big heat-sink.
Take note of the degree of moistness of the heat sink compound . . . .being thermally conductive . . .is it still that way ?
OR has the silicone oil creeped away laterally, and left that intermediate applied thermally conductive medium, now being merely a dry . . . . . and now being a thermally INSULATIVE . . . . layer of DRY tin oxide.

Place the unit so that the I.C. pins will be facing the ceiling.

Use a touch of rosin soldering flux / fluid to each IC pin and touch fresh solder to each pin and build up all of them to a big B-B size.
Confirm that almost all of your soldering iron is being well tinned and shiny. A rapid walking between those blobs with the tip at a slant, should have all of those blobs melted and that IC then being very easily extracted with a pull from the other side.
Clean off your excess solder blobs at BOTH positions .

Power up the unit with that transferred I C that is now being in either the 601 or 701 position and then test its pin 4 to find that errant minus voltage is then being way down to normal.
If that passes, then repeat the procedure with the other bad ( '601 or '701 ? ) to get another good IC into its hole.
Remember to clean off the excess solder blobs .
Check for a now normal reading on pin 4 of the new substitute.

If both sections pass, you can power up and expect to see no voltage being present at the initial transistor test point for the protection circuit.Look MOM . . . .no OP indication !
You then need to find 2 new IC's to replace the scavenged ones.

I am finding them as high as $28 or as low as .$18 over here in the bastard colonies. . . . . .no wait . . . .aren't you a bastard colony also? . . . . now . (pause) . .speaking . . . . . bastard to bastard . . . . .



73's de Edd

 

[onedog]

Sir Edd

(...aren't you a bastard colony also?) Yep, and I arrived as a settler back in 1948.

Pause to note that, with your help, I'm achieving my primary aim, i.e. to learn more about electronic repair rather than to fix the amplifier . One thing I know now (among many) is that de-soldering without damage is a special skill. I now need to learn to fix a damaged trace so I could be a little while getting back to y'all.

Onedog

 

[onedog]

Sir Edd (if you are out there)

I'm back from outer space with that sad look upon my face.

I've studied and practiced trace and pad repair and am ready to fix the pcb. I removed the 5 x IC amplifier chips and ran a diode check across each of the possible pin pairs. Readings attached.

Without knowing what I'm talking about and purely from looking at the readings, I believe that IC501 and IC701 are the only possibly good chips. Is that a fair assumption?

Onedog

 

[elebish]

Put a 75 watt incadescant 115 volt bulb across the ac fuse with the fuse removed so you can work with power on. If a short exists somewhere, the bulb will light up bright to act as a shunt to keep your boards from being damaged. Then isolate the short by removing the output transistors or large IC's first, one at a time! Also check for overheated components by touch.

 

[onedog]

Hi elebish
I'm out of action for a couple of weeks but will make use of your tip when I'm back. Thanks a lot.

 

[onedog]

Possibly a dumb question but we have a 240v system here and, through green power, a scarcity of incandescent globes. My choices appear to be Compact Fluorescents, Halogens or LEDs. Do you guys have any further advice on what will work instead of the 75W 115V incandescent suggested?

 

[davenn]

Possibly a dumb question but we have a 240v system here

yeah, no prob's, @elebish didn't realise where you were
75 - 100W 240V globe

through green power, a scarcity of incandescent globes.

I bought lots of them before they disappeared, still have enough to last a year or so

My choices appear to be Compact Fluorescents, Halogens or LEDs. Do you guys have any further advice on what will work instead of the 75W 115V incandescent suggested?

I have never tried using a compact fluoro's for this repair trick, they may work, but they may not have the same sort of response as a filament globe

try carefully and report back


Dave

 

[73's de Edd]

Sir onedog . . . . .

75 - 100W 240V globe
I bought lots of them before they disappeared, still have enough to last a year or so

If I interpret you as having a years cache of 240 volt versions of INCANDESCANT lamps, then a 60-100 watt version of one of those is what you will need to be using.

I believe that IC501 and IC701 are the only possibly good chips.

Check out your measurements again, but, his time, with heavy concentrating on the pin 3 to 4 aspects.

The bad units are being your IC601 and 701.
If you have all of the pulled units well marked ,then set aside the bad units and then reinstall a good unit at
IC 701 position and then do the:

Dim bulb test
Lamp installed in place of the main fuse for the initial power up test.
Lamp is BRIGHT on turn and stays . . . . .youse gots problems.
Lamp is slightly bright on turn on and then dims . . .OK.
If it passes the no shorts test above, then install the fuse in place and test out for sound from that units .
particular speaker.

With you expecting no overload / or / being in protection mode .

Then pull up another good IC unit and install at IC751 position with the same test procedure.

On a roll ! . . .?

Use the third and final good IC and install it at IC501 position.
If all is well up to that point, you should have a good working Right and Left channel for stereo and the Center channel as bass fill in.
You have now done all of this for zero parts expenditure.

Now, if you additionally wants that rear surround crap . . . . then you pays yer munneys and buys tew new Eye Sees for those final two IC601 and IC 651 power amp modules positions.

RELEVANT TECHNICAL REFERENCING:

73's de Edd