Dolby Pro-Logic; only central loudspeaker working Topic is solved

Radler · Post by **Radler** » 08 Apr 2025, 05:52

After checking for continuity on the cable loom and testing with a spare loudspeaker, I determined that the processor was to blame. Sadly I could not find a second hand processor for this system, so I decided to keep it simple and install a basic radio. Today I installed it on the car and finally I have sound in all loudspeakers; that is, except for the one on the dash, although I may bridge it to the original loom. I'll keep an eye in case a processor appears at a fair price, but it's not something that'll keep me from sleeping.

Thank you all for your help!

In case anyone was wondering, this is what the Dolby processor looks like inside:

Post by **abscate** » 08 Apr 2025, 05:57

Wow! The 1970s called and wants their circuit board back!

Radler · Post by **Radler** » 08 Apr 2025, 07:45

There are two boards; upon visual inspection I did not see any cracked solderings or burnt components, other than a weirdly-soldered ground terminal. Electronics are really not my thing so I can't say much more, I guess it could be repaired by replacing a couple of capacitors.

Post by **scot850** » 08 Apr 2025, 08:09

Unfortunately I don't have a spare. I'll check with my friend who pulled one from a V70R. He has a 850, so no center dash speaker, but although you can still use it it may not be worth it. Shipping will be the kicker, but if it comes available I'll let you know.

Neil.

Nikolaech · Post by **Nikolaech** » 08 Apr 2025, 08:48

Radler wrote: ↑08 Apr 2025, 05:52 After checking for continuity on the cable loom and testing with a spare loudspeaker, I determined that the processor was to blame. Sadly I could not find a second hand processor for this system, so I decided to keep it simple and install a basic radio. Today I installed it on the car and finally I have sound in all loudspeakers; that is, except for the one on the dash, although I may bridge it to the original loom.

Thank you all for your help!

Radio + amplifier work without processor.
Disconnect processor from radio and check.

Radler · Post by **Radler** » 09 Apr 2025, 22:56

Nikolaech wrote: ↑08 Apr 2025, 08:48Radio + amplifier work without processor.
Disconnect processor from radio and check.

Yesterday I tried my 2 Dolby head units (SC-900 & SC-901) with both amps and I can confirm that the system does not work without the processor, at least not in my case. In fact, not even the central loudspeaker: without the processor I can not even change the "mode" (normal, 3CH & Pro) in the head unit.

Nikolaech · Post by **Nikolaech** » 10 Apr 2025, 09:49

You have +12V power - OK
Speakers - OK
Processor-OK
Connection - sound blocking? (Tel. Mute)
if connected, disconnect and insulate this wire.

Standard connection from the manufacturer.
The color of the wires may vary.
Check.

: Сonnection_Volvo SC9xx.JPG (35.11 KiB) Viewed 106 times

Dolby Pro-Logic; only central loudspeaker working Topic is solved

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