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
Hi,
I'm new to this forum but have been restoring B&O stuff for some time.
I'm trying to fix a Beogram 6006 which stops after 1 second or so.
First o fall, I recaped the main board with quality components and checked cold solders at connectors. I also checked the carbon resistors and power supply, and tried a first test.When pressing Play, the optical arm lights up and the platter rotates, the LEDs indicate 33.33. Tthe arm moves toward the platter but hten returns to its standby position after having moved only for 2cm or so.The arm moves without trouble manually (so no blocking on the threaded shaft and solid shafts) and there's enough belt tension in both directions if I want to manually stop the threaded shaft.
I therefore checked the IR sensor at the arm motor: the emitter diode appears good with 1.2V across it (so at R1) and both sensors will cause the voltage at R2/R3 to pass between +14.7V and almost 0V.I also removed the control board which contains the <</>> light sensor. The light bulb is ok and the sensors seem to be ok because if I press Play, pressing << or >> causes the arm to stop moving until I release the button I pressed. I don't know the typical resistoance accross the light sensors so if anybody has a clue on how to make sure there is no problem on these please let me know.
I wonder what can cause this behavior. Any hints will be much appreciated.
Thanks !
Did you only recap the main board?The problem you describe is usually caused by the CPU resetting constantly, most often due toripple or noise on the supply, but could also be caused by bad connections at the CPU socket etc.
Martin
I didn't check that but reworked all connector solders. No change.I scoped the output of the two op-amps taking the signal from the IR sensor. Perfect shape during arm motion.However I can't adjust the voltage at the photoresistors of the << and >> buttons: their voltages stay between 1.7-2V after pressing Play and while the arm motor spins. Once idle, voltage slowly drops to 0V or almost. Adjusting screws B and A don't seem to change anything?I'll check the processor board but not sure if this is really the cause.I fully recaped the main board, changed the two caps under the platter as well but didn't change the one electrolytic in the cpu case. Not sure if this last guy is in trouble but will check as well.Note that if the cpu was resetting constantly, I doubt the arm would move up to the same position before it goes back to stanby.Thanks for your hints !
davidwinter: I'll check the processor board but not sure if this is really the cause.
I'll check the processor board but not sure if this is really the cause.
When you have done a few hundred of these decks, you'll be.
The cap inside the CPU housing is one of the most important caps. Check the schematics!And the CPU socket should be resoldered, - ideally replaced with one of the "tulip"-type.
I did the cpu board today:- 47µF/10V capacitor replaced,- cpu socket replaced with green tulip type,- many solders reworked (although only some cpu ones looked bad).After putting everything back, I tested again, but no changes.
Any ideas ? Thanks.
David
Put a scope to the supply rails and look for ripple and correct voltages.Check the adjustments for the << and >> buttons.
Supply voltages are ok.Both << and >> buttons seem to work, as I can increase the speed while the arm returns using >>, and also stop the arm while pressing << during return (the arm will continue returning once I release <<). However I couldn't get the 0.61V as shown in the manual. What would be the typical resistance of those light sensors with or without light ?I also scoped the near TR16 to see if I had the sawtooth as shown on the schematic. But I only have a constant voltage after pressing Play and unil the arm returns.So I scoped before C15 to see what came from the light sensor. All I could see a sort of small sine wage but negative.I also scoped at C16 / C17 to see whether I had something but here again I get a constant voltage after pressing Play and until the arm stops moving.C15 (2.2µF is ok) as all resistors around TR14.