ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Tonearm stops a couple of milimeters short of the lead-in groove;
- Wrong (to tight and/or to stiff) servo belt.- Dirt or wrong lubricant(s) on the threaded shaft/bushing.- Too low motor voltage at slow forward (small electronics mod. needed).- Wrongly adjusted search (button-) optos.- Bad LDR(s) in the operation panel.Any combination of the above.
Martin
Hi John,
you are most likely spot on with your diagnose - I have ordered some Murata Ceramic Caps and will probably throw all of these old trouble makers out.
not an exercise I am looking forward to perform - I keep an eye on the actual display decoder chip SN74247N as well !
all control panel adjustments are pefect as required.
there is also the uP control board I will revisit and check - the servo belt seems fine, the servo motor voltage oscillates between 0.96 - 1.26 VDC while
playing the record.
as described before, after a lenghty break it can work properly but after a few tries playing up again - just like something that has not been reset in a memory ?
it is not that the arm stops a few mm before the drop-down point, if it gets to that it works fine. The problem is somewhere else when it only travels one or two cm towards the center and swiftly returns for no aparent reason ?
lots to do, if there is development I will post again !
at this point many thanks for your patience, help and pointers 🤗
ALF
what happened In the meantime ?
new metal tachodisc from Martin has been fitted plus new servo belt.
in the processor box I changed the white old uP socket to a tulip-type / gold plated contacts and the C28 cap
plus reflew a number of suspicious solder joints.
I have not yet got those 4.7nF caps for the PCB 2 and those wheird dots on the display still appear!
Now, here is the strange thing:
pressing 'Play' may or may not work, carriage moves 1-2cm and returns most time straight away to its resting position.....
a uP initiated reset as Martin suggested ?!
if however I press 'turn' and then 'play' everything falls into place, arm moves into position, lowers and plays.
so far I tested this procedure more than a dozen times and it worked every time ????
I could live with that just to play records, but something is still wrong....! i simply have no further ideas where and what else to check ?!
suggestions are always welcome 😳
Weak power supply - in some way or another.Cannot handle both the (quite tough) startup of the eddycurrent coils and the movement of the carriage.If voltage is unstabile or not adequate, the CPU will be reset.
Thanks Martin,
that would explain the strange behaviour.
as said, going with 'turn' first and 'Play' to follow everything works fine !
i feel quite a bit wobbly to tackle that 'unstable power supply' issue.
are you pointing to a potential problem in those 'motor coils' drawing too much current or the two darlingtons BD441&442 ?
I am aware as it stands it is not properly fixed but with the 'detour procedure' I get the table to play records 🙄
A final remark to that perhaps "strange" procedure-detour
when I think about playing records I actually use the record cleaning function 'Turn' fairly regularly
as it seems silly not to clean/wipe before starting......in that sense it really does not matter, does it ?!
the BG 8000 now plays records again after weeks of blood sweat and tears......plus some work 😂
Time to 🍷 and enjoy the 📻
Hi Alf,
I finally ran those Beogram 8000 measurements you asked me for. I posted them here.
Regards,John
Hello John,
thank you very much indeed - they look very similar to mine 😉
I can now operate the BG 8000 just as normal and have put the cap replacement in the uP box on hold
despite still seeing the 4 dots on the display.....right now I am just happy the table plays records without playing up 🙄.!!
one thing however is a bit annoying which is a slight hum that I can't seem to get rid off completely.
one of these things that can have so many causes......
a cable from Steve at sounds heavenly already made a big difference.
cheers