Umatic BVU-950P Chroma playback issue - just bad alignment?
 

Having just salvaged this wonderful Sony BVU-950P Umatic machine from going off to the scrap heap, I was amazed to find that despite its age, it still works amazingly well :)

Certainly a testament to Sony who made it! :congrats:

Indeed the ONLY fault I can find (which may be the reason for it being discarded?) is a very slight chroma playback issue.

:question:

Mostly, it just was replaying everything constantly in glorious black and white monochrome!! :smack: BUT then taking time to warm the machine up a bit again (after non usage) - while going through the varied pile of tapes I suddenly found that a surgery training feature actually plays perfectly - with a full vivid chroma!
It even lights up the TIMECODE icon on the machine too!!

:huh1:
This has shown that the machine CAN display chroma correctly, and playback just fine!
So.... As colour hasn't totally failed, there must in my thinking simply be some small chroma misalignment somewhere??
:hmm:

From the uploaded photos you will see either there is no chroma at all, or there is... but it's certainly 'off' - suggesting something is just slightly misaligned.

Can anyone please help in maybe sorting this minor problem out, and solve where the fault might be?
:salute:

Amazingly it came with a maintenance manual too, and one can clearly see that in Vol 2 the Y/C demodulator circuit has been certainly looked at!!

Because of that I've checked the big PCB (DM55) for any work possibly done - and thankfully nobody has been 'at it' at all, so hopefully any fix should be easy, BUT I wonder if maybe some adjustment could have been either just 'out' from the machine's age, or worse something was 'twiddled' and that is causing a chroma playback issue on different tapes?

Any ideas?
Thanks in advance!
:D

Reference osc Adjustment....
 

Having now looked much more through the maintenance manual for this machine, and finding online some info regarding a VC93 All Format VCR Analyzer (which sadly I don't have!) :eek: ...BUT its PDF files (attached) do really help explain all about chroma circuits - and so checking the 4433.619 frequency at TP805 on the DM-55 board might be a great place to begin with, as that would certainly confirm IF that was well off mark, or not!

T501 is the easy adjustment for that.

Chroma springing to life after the machine warms up is usually a sign of bad capacitors. TP805 is just the PAL subcarrier reference (X501 generates the needed 4.43Mhz).