WM-D6C Since this information is not available anywhere on the web due to the unavailability of the CX20068/CX20218 datasheet, I decided to do some calculations and give you the reference Dolby output levels that you should get at the output of the Dolby IC, since this will be more accurate and won't require loading the output with 47K as the line amp measurement. The line amp has a gain of ~6.3 times at 315Hz where this adjustment is made, so given the reference Dolby level at line out is 340mV RMS, you should get ~54mV RMS at pin 27 of each Dolby IC with a Dolby tape (200 nWb/m ANSI). The feedback network of the line amp is exactly the same in all versions, so it does not matter if you are adjusting an older one with CX20068 or a newer CX20218 type.
WM-D3 The line amp has a gain of ~8.79 times at 315Hz, so given the reference Dolby level at line out of 340mV, you should get ~38.7mV RMS at pins 5 and 20 of the Dolby amplifier using a Dolby tape (200nWb/m ANSI). The Dolby amplifier used in the WM-D3 is the CXA1058M.
Hi Valentin, I have a D6C with CX20068. Do you confirm if I can change them with CX20218? I'm asking this since I can't find any CX20068 on the web, but probably the CX20218 is easier to find. If you know about any reseller that have one or the other please let me know, it would be much appreciated. Thanks a lot!
Why do you want to replace the CX20068 with CX20218 ? You made me curious. I do not know if the components around the Dolby circuit are identical in both versions, you need to check that yourself on the schematic. In regard to resellers of these chips, I don't know any that can be trustworthy. I don't even know how available they were back in the day given there were no issues around these ICs, so even the official SONY service centers didn't need them. I never seen these Dolby ICs going bad (their power line is protected by a zener so a reversed polarity power on won't affect them), this meaning there is no demand. Your best bet is to take it from a donor unit, but at that point I wonder why not simply sell your D6C and buy one with CX20218 instead if that is what you want.
Thanks for your feedback, Valentin. The problem is that there's no audio coming from the head, although the pre-amp section works fine. I gave it to a specialized technician and he identified the two CX20068 being the cause of the issue. Checking online I noticed that is impossible to find CX20068s but it seems that CX20218-T6 are till available somewhere. That's why I was wondering if I can upgrade those ICs. If you think that those two can't create that no audio issue, do you have any other idea? He also checked the integrated mute module but current is running fine there, and he also checked the head that works fine too. In a nutshell, if I play anything I hear hiss that gets louder turning the volume up, but no signal from the tape.
Hi Nycpan and welcome to Stereo2go. If both CX20068 chips appear to be faulty, check pin 20 on each chip. There should be 2.6V on each pin. If there is 0V on each pin 20, check C318 (this is shown as C138 on some schematics) and C305 to see if either is short circuit. It is extremely rare for the CX20068 or CX20218 chips to fail.
