[jqp]

My nOrh CD-1 was skipping when playing CDs. I turned it off and it seemed to have corrected itself. Then it started doing it again. Then it made the sound of bacon frying - static noises.

Hopefully it is just a tube gone bad - tonight it goes under the knife for replacement of the two output tubes, 12AX7.

Also while I am in there I will clean the transport assembly with dust-off canned air.

[jqp]

New tubes are in and it's as good as new, so far.

[jqp]

CD-1 (QDS-15) motherboard with the output tubes



the power section




remove tubes

[jqp]

old tube on right new tube on left




Is this a problem?

[JohnR]

Is this a problem?

It doesn't look great but could just be a botchy repair/rework job. What's the number on the chip?

[jqp]

I will have to get a better shot of the chips - I thought for sure i would have some in focus - need to take the chassis apart again tonight

[jqp]

It appears to be [ PCM1728E K9005A ]

... whic his a Texas Instruments DAC
   Audio D/A Converter ICs 24-Bit 96kHz Smplg CMOS D-S Stereo DAC










... and you can read the rest here

http://www.ti.com/lit/ds/symlink/pcm1728.pdf

[jqp]

The tubes seem to be burning in just fine

[JohnR]

Looks like flux. Is it still "frying bacon"?

[jqp]

No it quit making the crackling static when I changed the tubes - they had been in there over 10 years. The CD-1 was turned on at least 8 of those years 24x7! Not sure what the life expectancy is of the average 12AX7 tube is - another thing, there seemed to be more gain with new tubes?

[JohnR]

I would expect that the tubes are used only as buffers. Like in my old Cal Alpha. Though I never did understand why a 12ax7 would be used there. Anyway, 8 years 24/7 would be... um, 70,000 hours? Pretty good going, but probably well past the replace-by date.