828MkIII: Noise on 2 channels

[henris42]

Hi,

I tried to restore an 828Mk3. However, I have horrible, I'd say digital noise on ch 4 and ch 8 (I think - anycase 2 channels that are separate) .

I tried to oscilloscope the inputs to the ADC, but its all quiet.

For the PSU, all the caps have been changed in few years back. It had also bit issues on DSP boot, but I replaced the SMD cap next to DSP, which seemedly sorted that out.

I honestly have no idea what to do next. Should I probe the TDM on the DAC, if DAC is bust?

Any ideas?

[HCMarkus]

I honestly have no idea what to do next. Should I probe the TDM on the DAC, if DAC is bust?

I have far less of an idea than you, as you seem to have a solid understanding of how the guts of the MkIII work and I haven't much of a clue.

That said, I can follow signal flow, and seems that, short of somehow checking the analog output stage of the MkIII, you've covered your bases. Also, the fact the issue is on channels 2 and 4, and having some thought in my mind that the converter multiplexing scheme (there is such a thing?) may somehow tie 2 and 4 together, has me thinking the issue may lie within the converter.

Regardless, good luck!

The above is known in the construction industry as SWAG... Scientific Wild-Ass Guessing.

[henris42]

Yeah...

If the issue was analog, we weren't here...

[mikehalloran]

USB, FW or Hybrid?

[henris42]

FW version.

[mikehalloran]

FW version.

Ouch. At what point does this become a fruitless pursuit? Unless you find a used one with blown PS caps for next to nothing, it looks like you are stuck.

I see used 828mk3 FW around $180 and 828mk3 Hybrids in the $300 range on Reverb; 828x around $450… “High speed USB 2”, has a lower RTL than FW400, BTW,. Since the 828x has a FW400–TB converter, I prefer the 828mk3 Hybrid on price.

Then there’s the newest USB 3 MOTU 828 with the latest Cue Mix @ $995 everywhere. My only issue with it is that SMPTE has been dropped, not an issue for most of us.

[henris42]

Yeah it sure might be a tough one. I was thinking maybe the ADC has an issue, I might be able to probe that. Or the RAM - its DSP code so it likely uses the same addresses for buffers all the time. A service manual would be nice. I was wondering is there any self-test code I could try?

I got two MkII:s for rebuild (from eBay) as well, I'm sure I get "enough" working ones in the end. (really need only 2 for the current studio).

[henris42]

I investigated this further as I rebuilt an 828MkII as well - it has the same issue! Bit different channels, but in the end same issue. (MkII was like that out of the eBay box, no change after changing all electrolytic caps, including SMD ones.)
So I think it has to be something with the Firewire. I ordered another PCIe card, this time with a proper TI chip. (Current one is VIA). Lets see.

[HCMarkus]

I investigated this further as I rebuilt an 828MkII as well - it has the same issue! Bit different channels, but in the end same issue. (MkII was like that out of the eBay box, no change after changing all electrolytic caps, including SMD ones.)
So I think it has to be something with the Firewire. I ordered another PCIe card, this time with a proper TI chip. (Current one is VIA). Lets see.

Good thought! Hope flies for ya'!

[henris42]

Also verified on 2nd 828mk2, exactly same issue as in the other mk2. This one has actually rather swollen capacitors. I'll do total electrolytic change for this as well. Firmware upgrade for it was lets say interesting.

BTW, how many of these units you can have attached to a single computer? I know its 2 chained line in dedicated FW 400 line (potentially a fw host controller chip?), if you want 96kHz. But how many lines does the driver support? I was planning to start with 4 interfaces.

[henris42]

The Post was very quick, and I got a second FW card.

OMG, it works fine. This is older StarTech FW PCIe card (PEX1394A2V2), with TI chip and PCI-PCIe bridge.

Unbelievable, un-fscking-believable!

So the The VIA direct PCIe does not work!

[HCMarkus]

The Post was very quick, and I got a second FW card.

OMG, it works fine. This is older StarTech FW PCIe card (PEX1394A2V2), with TI chip and PCI-PCIe bridge.

Unbelievable, un-fscking-believable!

So the The VIA direct PCIe does not work!

Congrats!