Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Bad DSP board on G68?

The digital output on a G68 seems to be dead. The cable is good because it works in another system. Configuring the G68 through the front panel as well as through the RS232 port doesn't help. No output even with speaker calibration. There is an error message when configuring through the RS232 port that says unable to read from device. This happened right after I replaced the power supply. I did not find the tech note on power supply change until after I replaced the power supply so the pins were not changed to match the new power supply. I suppose that could have fried something. Pins configuration is correct now.

I wonder if this has happened to someone else and if so is there a known fix? Thanks.

One more piece of information. The configuration program recognizes a G68XXV whereas it's actually a G68J. That's not right. But it doesn't explain why the test tones don't work.

The DSP speakers are verified to be working by connecting them to another source.

The only bit of information I can offer is to make sure the voltage is correct and measured at the right spot on the PCB board. 5.0V will be too low and cause problems. It needs to be 5.2 volts to operate properly. You have likely seen this already but here is a link to the steps for the power supply replacement.

Thanks. I've tried that.

Before I swapped the power supply connector pins here is how the new power supply was connected to the G68 circuitry:

G68 rails 12V 5V 5V GND GND -12V
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XP PS rails 5V 5V GND GND -12V 12V

The risk here seems to be:

1) shorting 5V to ground risks damage to the power supply but not G68.
2) applying 12V to the -12V circuitry risks damage to G68. But I think the 12V rail is for the display, which works fine.

Hence, there isn't anything obvious that would explain why there is no digital output.

Edit: I drew lines between the G68 rails and XP PS rails to show the connections. But when I post, the lines aren't where they belong. Hence, please note they are connected in order as listed.

It is possible that you've done some damage by incorrectly wiring the new power supply. If you have a multi-meter, double-check that all the output voltages are correct from the PSU. Make sure that the 5v is set to 5.1volts (measure on the comms card).
Have you changed the electrolytic capacitors on the backplane? These do become leaky and even though you've changed the PSU, these will (if not changed) shorten the life of the new PSU.

In standby, press display a few times and check that the unit can see the DSP cards (look for DSPC xxxxxxxx / DSPD xxxxxxxxx & E / F - make sure that they're not zeros)

You could also try re-seating all the cards and cleaning the edge connectors, but that is almost an entire unit strip-down as you need to remove the back panels (lots of screws and bolts! - keep notes of what goes where!!)

It is easier to test each card separately in a known good G68 to find out if you have a faulty card. Some replacement cards are available, but are costly!

Please keep us updated on your progress.

Good luck,

Steve

The voltage measured at the voltage regulator on the comms card was set as low as 4.95V and as high as 5.2V. Right now it's at 5.12V.

The display shows that cards A-F are all non-zero values.

Hopefully it's just a blown electrolytic capacitor on the motherboard. Hopefully there is an easier way to get to the motherboard capacitors than removing the back panels and all the boards. If not, then it's turning into a bigger project. Oh well. I'll figure it out with all your expert advice.

I can share an issue I had with digital audio output on my rear channels from a G68D. I had audio output from my Main and Center channels, but no output on the surround channels. Neither changing the source nor trying the calibrate function would produce any sound on surrounds. I checked the speakers via a different source (no processor) and they were working perfectly. This was a head-scratcher!

I got some advice to try re-soldering the SPDIF connection on the digital output card from a friendly HH/dealer on here. Sure enough, this worked and the audio output was restored! I never received any error message though, so this may not be your problem.

Regarding replacing those caps on the G68 motherboard, I did that once too, I had to take the whole thing apart to get in there to do it.

Good luck!
John

I've had the RCA connector come loose too. For some reason those have always been too tight on all the G series component I've seen. That results in stressing the PCB connection when pulling them off. I know they have some strain relief, but apparently not enough. On the other hand, the power connectors on all G components have been on the loose side. It should be the other way. Firm contact greatly improves power transfer but good enough is good enough for low power signals.