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Is this an (unsuccessful) attempted modification to a Magnavox CDB560?
Is this an (unsuccessful) attempted modification to a Magnavox CDB560?
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Old 7th January 2018, 05:13 PM   #1
62vauxhall is offline 62vauxhall  Canada
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Join Date: Mar 2011
Location: Greater Vancouver Regional District, BC
Default Is this an (unsuccessful) attempted modification to a Magnavox CDB560?

A Magnavox CDB560 was offered to me at no charge. Other than being able to plug in to power it on (which it did) and insert a CD to see if it would read, track a disk, that the display & function buttons worked (all OK) I could do nothing more at that time.

There is no headphone jack so to listen on arriving home, I hooked it to an amplifier but there was no audio. There was however about 0.07 mv DC present at the outputs. Despite that "there was something there" my initial thought was the output jacks had come disengaged from the circuit board so I removed it to inspect the underside but the jacks were solidly attached.

It was then I noticed a "quad array" of what look to be 3.92K ohm 1% resistors soldered in place. I have seen the odd component soldered on the underside of circuit boards before but closer inspection makes me believe these were added after manufacture.

I intend on removing them to see if, somehow that restores signal to the output jacks. But before doing so, thought I'd ask here if anyone can speculate as to the purpose those resistors were intended to achieve?

They are in close proximity to op amps NE5535N

There was no Magnavox service manual on HF engine but there is one for the Philips CD560. I could not interpret much as I'm not very adept reading schematics and the resolution was not very good.
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Old 7th January 2018, 05:22 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by 62vauxhall View Post
if anyone can speculate as to the purpose those resistors were intended to achieve?
Probably "pull down" resistors from the op amp outputs to the negative supply,
to make the op amps operate away from the crossover region.
You can leave them or remove them, but it may sound better with them.

Last edited by rayma; 7th January 2018 at 05:27 PM.
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Old 7th January 2018, 05:59 PM   #3
62vauxhall is offline 62vauxhall  Canada
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Join Date: Mar 2011
Location: Greater Vancouver Regional District, BC
Quote:
Originally Posted by rayma View Post
Probably "pull down" resistors from the op amp outputs to the negative supply,
to make the op amps operate away from the crossover region.
You can leave them or remove them, but it may sound better with them.
Thanks, I assumed they must have been an attempt by someone to improve sound quality. However, I just now lifted a leg of each to disengage them and there is now audio passing to the output jacks.

Since they were disengaged, I tested them. Three measured as they were supposed to but one read a lot higher (11K~12k ohms) and was not stable. So I shall take the easiest course of action and leave well enough alone by completely removing all four and button up the player.

I have several of these cheap TD1541 based players (too many actually) and they all sound OK to me in stock form. A couple of years ago I decided to broaden my horizons with a newer CD player (only 16 years old at the time) and got a Rega Planet 2000. It sounds better but I'm not crazy about the top loading system. Can't put anything above or below due to clearance.
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Old 7th January 2018, 07:51 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by 62vauxhall View Post
I shall take the easiest course of action and leave well enough alone by completely
removing all four and button up the player.
Sounds like a good idea.
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