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Louie
Louie, Technician
Category: Home Theater-Stereo
Satisfied Customers: 1086
Experience:  Have been in the business 25+ yrs., down to component level.
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I have a dead A-9555 amp: fuse is good, no relay click, no

Customer Question

I have a dead A-9555 amp: fuse is good, no relay click, no pwr supply output.
Submitted: 3 months ago.
Category: Home Theater-Stereo
Expert:  Louie replied 3 months ago.

Hi Sid, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, a little more background info please:

  • • has it been in storage for a length of time;
  • • is this a sudden recent issue;
  • • perhaps after a recent storm, power outage and/or the likes;
  • • or slowly / intermittently developing while in use;
  • • any recent work, repairs or mods done.

Additionally confirm; performing a a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even a soldering iron?

Customer: replied 3 months ago.
It's been 'broke' for a while before that infrequent use, I've tried the protection reset
it's on a surge protector, no problems with other equipt - CD player, turntable etc
no work, repairs, or mods
this is a DIY and familiar with mm and soldering iron
Expert:  Louie replied 3 months ago.

Great on the DIY!

Proposed preliminary checks (if have not been done) on suspects:

  • • check switch S901 and fuse F901
  • • with the Onkyo unplug, check the resistance of the primary winding of the standby transformer T901;
  • • likewise check the resistance of resistors R906, R909, R910 and R913;
  • • with the Onkyo plug in, check the voltage at the cathode of D904;
  • • and when attempting to turn on, measure the voltage at the base and collector of transistor Q901.

A friendly reminder; voltage measurements by its very nature requires that the Onkyo be plugged in and therefore LIVE! Please exercise due care and caution.

Customer: replied 3 months ago.
Sorry this took so long had to stop a couple of times hope these are good readings - have a cheap meter, unstable
...S901 and F901 check good
...T901 pri (P901a - P901b w/ S901 disconnected)= 0 open .0LMohms
...R906= 2.5 R909= 109= 1.9 R910= .8 R913 = .7
...v D904 = 66.4 mv
...Could not find Q901, Q902vbc = 1.9mv
Customer: replied 3 months ago.
T901 change to P901B - P904A = 4.4k
Expert:  Louie replied 3 months ago.

The "...T901 change to P901B - P904A = 4.4k..." appears to be high.

Please check the voltage across C913.

Customer: replied 3 months ago.
4.3
Expert:  Louie replied 3 months ago.

Sid, it would appear that the issue would be with the standby voltage at C913 as it appears to be very low with a 4.3V reading. I was expecting something like 10~12VDC. Do you have a 12V power supply? ....that we can use to test

Customer: replied 3 months ago.
let me take a look
Expert:  Louie replied 3 months ago.

Yes please. (I sometimes use the power supply of an old desktop computer as it has several output including +5 and +12.)

Customer: replied 3 months ago.
I have Netgear transformer 12VDC 1A out
Expert:  Louie replied 3 months ago.

Should do the job.

Another firendly reminder; observe correct polarity.

Customer: replied 3 months ago.
Ok, measured 16.7VDC out will have to remove the plug. Where do you want me to attach it?
Expert:  Louie replied 3 months ago.

That would be the no load voltage.

First disconnect connector from main transformer T911 and the connector to JL901B.

Then feed this 12V source to the pins of C913.

Then measure again the voltages above posted.

Customer: replied 3 months ago.
I don't have access to C913 pins, I'll have to remove the PS bd or improvise a connection to the anode of D906 and the RLGND pin of JL901B. Any suggestions ?
Expert:  Louie replied 3 months ago.

I normally use alligator clips with wires similar to the products shown HERE.

Yes on the RLGND but perhaps you meant cathode of D906.

Customer: replied 3 months ago.
No alligator clips. Had meter lead kit until it got pinched by a worker from my garage along with my Fluke. Stand corrected on the cathode, (it's been awhile) - thinking may have more room at R906. Do you need a special tool or procedure to disconnect JL901B.
Expert:  Louie replied 3 months ago.

Depending on the version, JL901B may be plug in or soldered.

But we can try even with it still tied to the board.

Sorry, no board layout just the schematics so could not suggest alternative test point.

And yes R906, R909, D906 all would serve as tap point to inject the external +12V.

Customer: replied 3 months ago.
Louie
Are you avail this afternoon? I am not making progress with this step and it's after 3. I have an appointment early am, can we take this up later in the day?
Expert:  Louie replied 3 months ago.

I understand and no prob; later when able.

Please do a Ctrl + D to bookmark this page or click on the link sent by the site.

I would be prompted soon as you post an update.

Customer: replied 3 months ago.
Thanks and good morning.
Expert:  Louie replied 3 months ago.

Cheers.

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