Sony STR-K750P STR-DE495P protect mode yay!

[Navarone]

I'm having the protect mode problem with a sony receiver, but with different results after testing. I have a schematic and a fluke 179, so I'm kinda half way there! http://www.electro-tech-online.com/a...-29-pdf.34261/

So I checked solder connections, redid a few, didn't look bad at all, that didn't fix it. Started checking voltages, front left and right and surround L/R ICs have the correct +/-53v input, (forgot to check dc offset), center channel measured behind the output safety relay (because it was easier to get to, but it's after the chips on the heatsink) has -53v. that should be close to 0.1v dc offset right? So I desolder pin 7 on IC501 STK350-230, still in protect mode, but now 0v on center relay and +15v behind relay on Front L/R Surround L/R, Ok, weird. Desolder pin 9 on IC501, no more protect mode, can go through menus and everything, but now +53v is missing at IC701 and IC702, so no sound, and now 0v behind relay on Front L/R Surround L/R. (in reference to ground, like a dead short 0v, no floatyness)

I beep tested pins 7 & 9 to pin 5 on IC501, no beeps, no nothing, forwards and backwards. Same thing on IC701 and IC702, so maybe it's faulted open? I also compared all the Q's on the heatsink and they all looked exactly the same except for the one for the center channel, it beeped once and then "OL" on the meter, and intermitently beeped, not every time.

Start looking for the path that gets +53v from the rectifier to IC701 and IC702 and find a "flame proof" 1ohm resistor R732 that's dead open, but it's hidden under 2 different criss crossed shunts, so It won't be coming out without a fight! That's the only way to get +53v into those IC's, so I guess it's bad. Start poking around for a ground short on the +53v rail and I'm not getting anywhere productive. Some times it beeps and some times it doesn't. I think the meter is confused with the rectifier and caps. So resistor is pulled and confirmed bad.

Think if I short the 1ohm resistor (or repalce it with a new one) I'll get the +53v back? And with the +/-53v pins desoldered from the STK will I blow up anything? Did I mess something up by desoldering only one leg on the STK350-230? Let's say I get a new resistor and a new STK, think those are the only problems or am I just going to smoke them too? Was I going completely backwards?


Thanks!

[Navarone]

Re: Sony STR-K750P STR-DE495P protect mode yay!

Ok, update.

Replaced the blown 1ohm with a 1.2ohm because it was $2 for 25 and they only had that and 2 total 1ohm in stock, so if I blew up a 1.2ohm it wouldn't be bad since I have 24 more.

So now I've got music on all four channels except center, which I desoldered both +/- 53v inputs. I'll be getting a new STK350-230 soon, I don't want to take it apart again to fiddle with it until I get the new one.

The next problem is the volume, even at max it's probably only about half of what it could be. Is that 1.2ohm resistor on the +53v rail causing that much of a drop in volume? I'm measuring 53.5v and 53.4v before and after the resistor. I'm measuring 1-9mv dc at all the speaker terminals and 1-2.2v on IC701 and IC702 on pins 2, 3, 11, 12 in reference to ground. Am I supposed to measure them across 2-3 and 11-12? I get 1-2.2v across them. sooo....?

[Navarone]

Re: Sony STR-K750P STR-DE495P protect mode yay!

New STK350-230 from MCM fixed the center channel, but the volume still seems low, even at max volume it's like half the output of my PCA3 or even the LP-2020A+. I replaced the 1.2ohm resistor with a 1ohm and can't tell the difference. It is loud and clean, but not like "WOW THAT'S 100W PER CHANNEL!!" I am using cheap 4 ohm speakers to test it though. Think it's just made for the crappy little Sony HTiB speakers it comes with and will sound fine when returned to the customer?

Any ideas?

Thanks!

[Longbow]

Re: Sony STR-K750P STR-DE495P protect mode yay!

So now all 5 channels work and are distortion free? That would be a fix. What is the power output of the front L-R channels?

This unit appears to be rated at 100w total for all 5 channels, since it comes with tiny computer speakers. Apparently the owner also figured the unit should put out 100 watts per channel. Figures.