LaserDisc Database :: View topic - [MDP-450/650] Player repair info needed

LaserDisc Database https://forum.lddb.com/

[MDP-450/650] Player repair info needed https://forum.lddb.com/viewtopic.php?f=56&t=9253	Page 1 of 1

Author:	widget [ 30 Jul 2020, 01:30 ]
Post subject:	[MDP-450/650] Player repair info needed
I have had my player since about 1993 and after about 10 years it would not reliably load disks or open/close the tray. It would run the loading mechanism with ratcheting noises whenever it powered on without a disc in the tray. So, not having time to open it up I abandoned using it until recently. The original problem was easily fixed with a new belt, but things quickly went downhill after playing only part of one disc....it would skip to a completely different track and eventually stopped reading either CDs or LDs. So I ordered a "new" laser head and installed it, but before I could get the new head verified it refused to spin up while the head attempts to read the disc. I have verified the spindle motor is good and the laser is attempting to focus on the (stationary) disc. So here are my questions, referencing the repair manual System Control board. 1) The System control board has 4 signals out to the spindle motor circuits. SP OFF, 2FH, SP ERROR, SP UNLOCK. When I press PLAY the signals are 0V, continuous 5V pulse, -5V, and 0V. I assume the 2FH is to control spindle speed and the SP ERROR indicates direction and speed. So what are the correct states of SP OFF and SP UNLOCK? And are they active high (5V) or active low (0V)? 2) Does anyone know what inputs to the control chips determine whether the spindle motor should spin? 3) Any insight into the control chip logic would be greatly appreciated.....

Author:	odotb3 [ 30 Jul 2020, 08:32 ]
Post subject:	Re: Sony MDP-450/650 player repair info needed
Could the issue be related to the new laser? Maybe the new laser is having trouble focusing and is causing the spindle motor to refuse to spin? I believe the installation of a new laser requires recalibration of the whole laser assembly.

Author:	widget [ 30 Jul 2020, 21:23 ]
Post subject:	Re: Sony MDP-450/650 player repair info needed
I read or saw somewhere online that a new laser does not require recalibration. But either way I put the old laser back and the spindle does still not spin up. This problem was intermittent before I obtained the new laser and became permanent after it was installed. I read in these forums that the optical device chassis (and optical laser) must be "raised into position" before the spindle is started, which may be a clue to what is wrong, but I don't know what tells the system control board that this has happened. Since the laser is on and trying to focus I don't think it requires data from the laser because there won't be any unless the disc is spinning. Does anyone know if this is the case? If I had to put money on anything I've observed it's that SP UNLOCK to the spindle motor drive circuits must be active, and if it is active high that is not the case.

Author:	laserpaal [ 03 Aug 2020, 18:38 ]
Post subject:	Re: [MDP-450/650] Player repair info needed
I swapped the whole laser assembly including the spindle motor from a MDP-850 to another. I maintained the original pot adjustments and did not alter them in any way. Maybe I was just lucky this time, but lo and behold, it works as it should. Yeah, it could have been adjusted and tweaked, but more importantly it works and reads the discs well. I need to look more into the sticky clamp problem.

Page 1 of 1	All times are UTC [ DST ]
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group http://www.phpbb.com/