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

[Radler]

Hi there.

This is a 1998 V70 I bought recently and the seller already mentioned this issue. Today I took a look at the amp below the passenger seat could not see any issue; the connections look clean, the wires do not seem to be damaged and and inside the amp I do not notice any damage. After reconnecting the amp the issue persists. This means that in the normal mode there's no sound at all, and in "3CH" and "Pro Logic" modes there's sound from the central loudspeaker.

Has any of you had any similar experience? Do you have an electric diagram for this system so I can start checking individual wires?

Thanks!

[BEJinFbk]

98 S-V70 Fuse Locations and Legends.pdf

(678.65 KiB) Downloaded 69 times

98 V70 Radio with AMP and Dolby.pdf

(650.35 KiB) Downloaded 29 times

[Radler]

Thanks for the diagrams! At least now I can start checking if the amp is getting power. A user in another forum said that the central loudspeaker is powered by the head unit and not by the amp, which would make sense in my case.

[scot850]

They are correct. There is a Dolby driver unit though mounted behind the head unit which plugs into the back of the head and then the center speaker is driven from the back of the head as mentioned.

The amps to die, but I have only ever had one bad one I returned as it had been under water at some point!

There should be plenty out there. I have 7? spares and cables kicking around as I tend to hoard them when I find them.

Dumb question, is the wiring harness to the amp under the seat connected to the original harness?

You could disconnect the added harness and plug the standard connectors into the back of the head unit and see if your speakers are working at least. The connectors are both behind the head unit under the dash.

Neil.

[Radler]

Thank you everyone for the replies. Today I found some time to take a look at it and I could get the following. With ignition and radio on:

- The amplifier is getting battery voltage at pins A3 and A4. I measured this voltage using (separately) pins A9 and A10, which also means that ground contacts work properly.

- I could only get 12V at the central contact of the DIN connector. I do not know what each of these pins represents.

- With all plugs connected, I could not measure a voltage in any of the pins in charge of feeding each loudspeaker.

This makes me think that the amplifier itself is not working. I also could not measure any amperage at the power wires with the plug connected, which I assume is due to the amp not working, although I do not really trust my multimeter in terms of amperage measurements.

I will try to find an amp, although it doesn't seem to be easy to find one for this year model.

[scot850]

If there was an easy way to get one to Germany I have 7 or maybe 8 of them.

To confirm it is bad, if you have any Volvo radio other than the SC-900 or 901 (no internal amplifiers), you can run the system without the amp to test the speakers.

The original connectors will be behind the radio and if the radio was fitted by Volvo when new, they wrapped some one sided sticky foam over the connectors to stop them rattling behind the dash. Disconnect the 2 connectors and stick them in the back of your radio and see what happens. At least you can confirm either the amp or the cable from the amp is bad.

Connector harness from standard radio harness to amp

2 connectors that connect to original radio connector to amp

Connectors from amp harness to radio.

The last picture shows a connector with only 1 yellow/black wire to it. The original had a bunch more, but that is because the amp harness connects to the speakers directly.

Good Luck!

Neil.

[Radler]

If there was an easy way to get one to Germany I have 7 or maybe 8 of them.

To confirm it is bad, if you have any Volvo radio other than the SC-900 or 901 (no internal amplifiers), you can run the system without the amp to test the speakers.

The original connectors will be behind the radio and if the radio was fitted by Volvo when new, they wrapped some one sided sticky foam over the connectors to stop them rattling behind the dash. Disconnect the 2 connectors and stick them in the back of your radio and see what happens. At least you can confirm either the amp or the cable from the amp is bad.

(...)

Good Luck!

Neil.

Thank you for the answer, I find it very insightful. Since a simple radio is significantly cheaper then the amp (30€ vs. 100€), I could start by testing with a non-Dolby head unit. I see only one problem with this: as I said, at the DIN connector I could only measure voltage at the central pin, which corresponds to power terminal, but I could not measure a voltage at any of the other pins. This makes me wonder if the problem may lie at the head unit not sending any signal to the amp. Or maybe that signal is not measurable with a simple multmeter?



I wouldn't mind too much about replacing the head unit with a common one; anyway the CD reader is not working properly.

[scot850]

What head unit have you got? SC-XXX?

Neil.

[Radler]

SC-900 or SC-901, not sure.

[scot850]

Ok, I can't quite make out what the front of the head unit says. It is definitely an SC-900 or 901 unit based on the 3 CD changer. In that case you cannot test the speakers the way I suggested as the head unit has no internal amplifier like any other SC-XXX units.

You do need the amplifier in this case to drive the speakers.

The writing just below the right end of the 3-CD cassette tells you which unit you have.

Until recently we could buy the head units at our local junkyards for $10 CDN, maybe $20 when not on sale. Recently prices have been doubled or more which no one will pay for these.

Check your local craigslist or selling site and look for an SC-815/816 head unit with a single CD player or someone parting out a P80. You can fit any radio from a P80 to check the speakers out. The only downside is I seem to recall only the SC-900/1 units have the Dolby connection on the rear if you have the center speaker. As you know that already works, then I's suggest the likely issue is the amplifier as you suspect.

If you are not too concerned about the Dolby center speaker, then try one of the cheaper units and at least check the speakers all work.
Just don't go this crazy...............!

Test system for radios and speakers

Good Luck!

Neil.