Sony STR-DB940 help..

I just got this unit. It powers up and the protection kicks in. I've repaired a 840 with this same problem. but it appears on this unit the 15 volt regulator gets real hot. I've replaced it already with the same results. If anyone has any tips or pointers to where to look I'd appricate it.

-Ron

Reply to
Ronald
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I just got this unit. It powers up and the protection kicks in. I've repaired a 840 with this same problem. but it appears on this unit the 15 volt regulator gets real hot. I've replaced it already with the same results. If anyone has any tips or pointers to where to look I'd appricate it.

-Ron

Reply to
Ronald

If the 15 volt reg gets hot, it seems to me there's some IC or other loading it down. I'd sub in an external 15 volt or so and see what gets hot.

Mark Z.

Reply to
Mark D. Zacharias

I just got a schematic for it. Traced back to the diodes on the dc power board. Gonna replace them tommarow. Odd readings on the diodes, in diode test i tested it both ways one reading of 1.1 and .5 and a few just .5 in one direction. my guess from my repair work on pinball machines .4 - .6 is ok diode but could possiable failed diode. But I'm replacing them with new ones. to ensure a rebuilt power supply.

-Ron

Reply to
Ronald

Follow-up Bump..

I've replaced the diodes, still no change. I got a schematic off the internet. finding a short in the 15 volt line is tough. my thoughts if I unsolder the parts in the line it should resolve the short. Replace them one by one until the short shows up. Sounds logical?

-Ron

Reply to
Ronald

That's why I recommended subbing in an external 15 volts or so (with the unit turned off and unplugged) and see what gets hot. Much quicker and easier. Helped me fix many a unit. These pieces are so complicated that tracing everywhere that 15 volt line goes would take way too much time and effort.

Mark Z.

Reply to
Mark D. Zacharias

should I tap anywhere in the 15 volt line? chassis ground or pcb ground.

-Ron

Reply to
Ronald

The way I would suggest is to remove the 15 volt regulator (positive 15, I assume) and connect the positive lead from the power supply right there or at the capacitor which would usually follow. The ground of the power supply would connect to chassis ground. If the supply is adjustable, you can start at a lower voltage.

The shorted or leaky part is probably on the DSP board or an input switching IC near the inputs, or maybe one or more bad op-amps.

One thing. If it's really a dead, dead short, i.e. zero point zero ohms, then just feeding your power supply into it might not reveal anything, since some resistance is necessary in order for the bad part to generate heat. This is pretty rare but I have seen it happen. However, your regulator IC would probably just shut down if this were the case.

Mark Z.

Reply to
Mark D. Zacharias

With your help we found the short. it in two switching chips... I need some help locating them.

Toshiba TC9273N-004 and TC9273N-013 these both got real warm and one let out a puff of smoke :) so we nailed it.

Thanks for all your help if you have any insites... let me know

-Ron

Reply to
Ronald

Get the IC numbers off the board and you can get order them from Andrews Electronics. Their number is 800-289-0300.

Also, I have seen the TC9273N-004 from Onkyo cheaper. Not sure about the other. Their number is 800-229-1687. They can look up the generic Toshiba numbers you gave - at least they've been able to when I called on one before...

Mark Z.

Reply to
Mark D. Zacharias

Got my replacement parts in no dice. One gets real warm. I'm thinking this amp is screwed. I've only put about 30 bucks in parts into it. I have no clue what else to look for.

-Ron

Reply to
Ronald

I don't think those chips get warm normally. Could be one of the plus or minus 15 volt lines is high. You could still have a blown channel, or a bad voltage amp IC...

Mark Z.

Reply to
Mark D. Zacharias

Now when I put the new chips in, I unsoldered the amp transistors all of them. I can unsolder the zig zag'd ic's I had to replace one of these in my other receiver that had a protection issue. the -15 volt line seems stable its not warm. the +15 line is hot to the touch. But not scolding hot like it was before. its about the same temp as the -15. i can go though and unsolder the ic amps and the transistors amps, and unplug the bias's. One thing odd that I noticed. when I plug in the tuner module the amp goes into protection mode right away. I happen to have an extra module. plugged that in and got the same results. Now with these replacement chips I got the Toshiba TC9273N-004 and TC9273N-013 I found a toshiba tc9273n-007 this is what I replaced them with assuming the pinouts are the same. my guess is they aren't . I don't know where to get some information on these. I can order the 'correct' chips from andrews like you recommend. But thats what I have done so far. Mark I appricate all your help! Most people would stop and not bother to help. You stick around. :) Thanks for that bud!

-Ron

Reply to
Ronald

The tc9273n-007 would not be interchangeable. These chips are pretty special.

mz

Reply to
Mark D. Zacharias

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