No Sound o/p from SONY HT-BE1

[Old Sparky]

To clarify;  There is no sound from any of the 6 channels on this Home cinema amplifier when a signal is applied to the analogue audio i/ps, either from an audio sig. gen. or from my MP3 player.  The following symptoms have been observed;
1) When powered up & switched on, the centre rail voltage at any of the 6 speakers rises to ca. 7.63vDC over about 20 seconds and is then stable
2) The unit powers down after about 3.2 minutes with no signal i/p,with little or no switch off thump, but if swiched off via the on/standby button or at the mains a considerable thump is heard in the buit in wooffer. The Thump is at the same level regardless of the volume control setting.
3) Current consumption appears to be normal at around 60-70mA quiescent.
4) According to the display, the function switch is working, but a quick perusal of the block diagram suggests that the fault is in either the electronic switching or preamplifier circuits.

Does anyone 'out there' have any experience of this model, and have any idea as to what may be the cause of the faullt and whther it is repairable?   No-one appears to stock any specialist spares for these amplifiers.

[Old Sparky]

Having cosulted the Owners manual, I read that the system is designed to power down after approx. 3 minutes if no signal is detected, but I haven't checked further as to why no sound is produced from the 'line-in' RCA Sockets, or whether the 'switch off' thump is a normal thing for these amplifiers. Never having come across one before, I don't know. The 6 channel amplifier uses I.Cs in a typical bridged circuit, producing, according to the manual, 30WPC.. Hopefully the fault is repairable if and when I can determine the cause!

[Mark Hennessy]

The service manual is attached...

The voltages seen at the loudspeakers look normal to me - it's a bridged circuit running from 15V. The output amplifiers are TDA7384, which are pretty generic chips used in car audio, etc, so should be easy enough to source if needed. In fact, quite a lot of the silicon is non-Sony, which is good news.

Have you checked all the power supply rails?

Next, have you checked the operation of the muting circuitry?

Have you tried with a digital source (just need to hook up a DVD player)?

In-between the stereo analogue input and the audio amps is a bucket-load of complicated stuff. The audio is converted to digital and passed through DSP (IC802) which presumably does a Dolby Pro-Logic decode, or perhaps one of Sony's own "make surround from stereo" algorithms. There are also digital inputs - S/P-DIF or TOS-LINK, which will be carrying 5.1 Dolby Digital or DTS, which the DSP is able to decode. Finally, there's a USB input, which is basically the playback side of a USB sound card on a single chip, generating analogue audio that gets converted straight back to digital using the same processing as the basic stereo input.

Who was it that said "Big chips don't fail"? Let's hope he was right

All you can do is get the 'scope out and start analysing. Follow the audio through to the codec chip IC804. If analogue audio is making it to pins 29 and 30 (Left) and 31 and 32 (Right), that's good...

Next, does audio emerge on pins 23 (Centre), 24 (Sub), 25 (Rear L), 26 Rear R), 27 (L), 28 ®? If there's anything on any of those, that's good because it puts the problem somewhere between the codec and the audio output stages.

After that, there are some buffers and a volume control chip. All good analogue stuff that can be 'scoped. That's followed by some EF buffers, a LPF made from op-amps, more muting transistors, and the power amp ICs. Lots of complexity on the muting control side, as always.

The trouble is, understanding the schematics will take some time. Troubleshooting is not exactly easy with this sort of stuff - lots of surface-mount to contend with. And if it's one of the big chips, then you might be stuffed (if you can source them, can you change them?). From a quick Google, it appears that they are not the most reliable product in the world. For me, it's one of those quick "I'll check it's nothing daft", because anything more elaborate won't be economical... These are up to 12 years old now - that's not a bad lifespan for a modern bit of gear. Let's hope it's something age-related like dry joints or bad capacitors... At least it pre-dates lead-free solder.

Good luck,

Mark

[Old Sparky]

Morning, Mark,
I have a DVD Playerwhich could be used to test the digital input, but not the cable, as I use it with normal RCA leads for audio,, and a SCART lead to connect to the TV. Did think of using my MP3 player via the USB i/p to check that i/p. MY Oscilloscope has been out of action for ages, which doesn't help, I know, but I never seem to get around to trying to repair it. Thanks for the link to the Service maual, btw, but I have already downloaded it from the interneet. Like most modern gear, it is, as you say, a complex piece of kit, and takes some understanding. I've worked out part of the signal path at the i/p, and am fairly certain the audio amplifier stages are working OK, so I'll have to hope it's an easy fix, having also dicovered via Google, that they aren't the most reliable of products.

[Old Sparky]

Having carried out further checks since my last post, there is still no sound from any speaker, when using the regular audio inputs. I haven't tried the USB i/p, but have been trying to locate the switching IC-don't have it's circuit ref. to hand, but it's an 8-pin DIL device, almost certainly SMD somewhere in the rear RH corner of the PCB. If, when I locate that device, I still get no sound 'downstream' of that, then, as Mark suggests, it may not be worth proceeding any further only to find that a ' no longer available' multi-pin SMD chip is the cause of the fault!

[Old Sparky]

To correct the above post,, the switching IC is a 14Pin DIL Chip on the component side of the board in the rear RH corner. If no signals 'downstream' of that, then further investigation is required

[AlanBeckett]

Any Numbers on it?
It may not be the Chip itself, possibly the Logic Signals controlling it.

Alan

[Old Sparky]

The HT-BE1 has been put on one side, and I may go back to it after Christmas in the hope I can trace the cause of the fault!!