Semi-conductor substitute advice?

62vauxhall

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#1
I hope to dip into the Trough of Knowledge yet again.

This relates back to the NAD 502 CD player in which I wanted to substitute LED's to backlight the LCD display. I got that sorted out but induced a couple of subsequent problems. The first was that I killed power to the laser assembly /spindle motor. This could have been because I left the power on when soldering the lamp leads. There was a spark when the soldering iron tip contacted the chassis. After that, there was no movement of any kind from the laser pickup and the spindle motor didn't turn.

Yes, leaving the power on was stupid but it gets better.

I unfastened the board and not thinking because the power was still on, let it sit foil side down on the metal chassis as I started fumbling around looking for the point where the laser/motor was getting power. Something shorted and caused a 16v 100uF capacitor (C517) to explode. I replaced it but both of the two fuses blow on power up so obviously there was more damage. There is an NE5532N opamp (Q204) that I think was involved and will be getting some of those this afternoon. I also suspect IN4002 diodes were affected but I should be able to get those at the same time.

There is another semiconductor (Q507) I've never needed to concern myself with before that seems to be the "brains" behind power distribution and I think it's cooked. The part number is TA7256 or alternately, KA9256. My ability to read data sheets is feeble at best and I have difficulty enough with NPN/PNP transistors. This device is more complex and it baffles me. If anyone knows these things well enough to recommend a substitute, I would like to try replacing it.

TA7256P.jpg_640x640.jpg
 
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62vauxhall

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#3
As it happened, I visited one of the three local parts shops which has been in business for decades and do still have some out of production stuff on hand. Such was the case here as I was able to get the original IC. After installing it and a quad of diodes, the display bulbs are working but there is still no movement of the laser head or spindle motor.

Looking at the schematic, there are 3 pairs of transistors which look to be between the newly installed IC and the laser/motor assembly. Their part numbers are 2SD1225 and 2SB909.

I checked them for the voltages that the schematic says are supposed to be present and most readings were either low, nonexistent or exhibited voltage where none should be. Using my DMM's diode function I believe correctly, they all tested bad in circuit.

The only data sheet I could locate on line is in Japanese (I think) and with that plus some text info from other sites, I gleaned about 4 specs. Yesterday I spent about two hours and the same again today trying to find something to substitute but had minimal luck. Add to that, I could not even determine what the case style is called.

IMG_3171.jpg

Glen (grapplesaw) was kind enough to advise me of the website, http://www.findchips.com to locate a particular diode so I tried it to find these transistors and it directed me to Quest Electronics in California. Their website indicated they have a few of both original transistors. Unfortunately they have a minimum order so with approximately $10 shipping, the total is going to be $35. And since I'm in Canada, more like $45.

Am I nuts for even considering spending that much on 6 transistors? As far as I can tell they are for motor control not audio amplification so how precise would a replacement need to be? That said, they are in complimentary pairs so would paying nearly $10 per transistor be the best option?
 
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Gepetto

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#4
As it happened, I visited one of the three local parts shops which has been in business for decades and do still have some out of production stuff on hand. Such was the case here as I was able to get the original IC. After installing it and a quad of diodes, the display bulbs are working but there is still no movement of the laser head or spindle motor.

Looking at the schematic, there are 3 pairs of transistors which look to be between the newly installed IC and the laser/motor assembly. Their part numbers are 2SD1225 and 2SB909.

I checked them for the voltages that the schematic says are supposed to be present and most readings were either low, nonexistent or exhibited voltage where none should be. Using my DMM's diode function I believe correctly, they all tested bad in circuit.

The only data sheet I could locate on line is in Japanese (I think) and with that plus some text info from other sites, I gleaned about 4 specs. Yesterday I spent about two hours and the same again today trying to find something to substitute but had minimal luck. Add to that, I could not even determine what the case style is called.

View attachment 26783

Glen (grapplesaw) was kind enough to advise me of the website, http://www.findchips.com to locate a particular diode so I tried it to find these transistors and it directed me to Quest Electronics in California. Their website indicated they have a few of both original transistors. Unfortunately they have a minimum order so with approximately $10 shipping, the total is going to be $35. And since I'm in Canada, more like $45.

Am I nuts for even considering spending that much on 6 transistors? As far as I can tell they are for motor control not audio amplification so how precise would a replacement need to be? That said, they are in complimentary pairs so would paying nearly $10 per transistor be the best option?
Have you looked on eBay for a donor machine?
 

62vauxhall

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#5
Have you looked on eBay for a donor machine?
Yes, active and sold listings both just to see what prices plus shipping were but it would't be cost effective. And I'd have the carcass to deal with. I have a few of those kicking around all ready. Too many actually considering I have a one bedroom living space of less than 800 sq.ft.
 

62vauxhall

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#6
This morning I extracted all three transistor pairs to check out of circuit and one pair was cooked. The numbers for the others though looked to be OK so either my in circuit testing was faulty or something was affecting the readings because more than the one pair did not look good in that circumstance.

I spent considerable time again today searching for suitable substitutes and thought I found some a hell of a lot cheaper than the $3 apiece originals from Quest Electronics. But, as luck would have, they too were from Quest so their minimum order and $10 shipping charge still applied. Although I could have gotten a larger quantity of the substitutes, I went with the originals.

One of the subs had the suffix TV2 and I could not find any explanation as to what that meant anywhere. I learned here that suffixes could indicate packaging methods or lead spacing but I also read it could mean a different spec parameter - perhaps hfe. As mentioned, because these transistors seem to function as voltage distributors and not knowing if a deviation might be good bad or indifferent, I thought it was safer to drop in the same thing rather than an unknown commodity.

Must say though that I'll be righteously pissed if the spindle motor and laser head still don't work afterward.
 

laatsch55

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#7
If they are part of the same circuit or used in parallel they all could test bad UNTIL out of circuit...
 

laatsch55

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#9
Yep, that's why you never know for sure unless something is out of circuit....
 

62vauxhall

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#10
I picked up those hideously expensive transistors this morning and installed them. There is now power going to the CD player's laser sled/motor assembly but things ain't right. After turning on the power, I watched the laser sled slide toward the spindle, then stop when it got as far as it could go. AT the end of travel, there is a what seems a 60Hz buzzing sound which, though I cannot say for sure, sounds like the laser focusing mechanism rat-a-tat-tatting. The lens moves up but does not bob up and down which is what I understand it's supposed to do.

The assembly is a KSS-210A. Any guesses as to what might be wrong? Maybe a logic IC?
 

orange

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#11
Does the disc spin up when you insert it?
 

62vauxhall

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#13
No, the disc does not spin. but it does twitch clockwise once the laser pickup moves inward as far as it can go - when the buzzing noise starts.

Thanks for the link. Previously I scanned through it when looking at power distribution problems but again now for motion issues and saw there is something called a limit switch. There is nothing identified as such in the SM diagrams but there are 2 or 3 "switch, leaf", one of which I assume performs that function.

As I looked for said device in the player itself, I did happen to see that the "buzzing noise" was caused by the sled motor's gear teeth ratcheting against those of the larger reduction gear that drives the sled. The motor kept turning after the sled reached maximum inward travel. I experimented by pushing the switch I was looking at closed with a bamboo skewer but it did not disengage the motor - maybe the wrong switch? Next I will remove from the chassis, the whole transport to get a better look at it's underside and therefore that, other switches and associated wiring.
 
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orange

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#15
No, the disc does not spin. but it does twitch clockwise once the laser pickup moves inward as far as it can go - when the buzzing noise starts.

Thanks for the link. Previously I scanned through it when looking at power distribution problems but again now for motion issues and saw there is something called a limit switch. There is nothing identified as such in the SM diagrams but there are 2 or 3 "switch, leaf", one of which I assume performs that function.

As I looked for said device in the player itself, I did happen to see that the "buzzing noise" was caused by the sled motor's gear teeth ratcheting against those of the larger reduction gear that drives the sled. The motor kept turning after the sled reached maximum inward travel. I experimented by pushing the switch I was looking at closed with a bamboo skewer but it did not disengage the motor - maybe the wrong switch? Next I will remove from the chassis, the whole transport to get a better look at it's underside and therefore that, other switches and associated wiring.
You know, this kind of stuff would seem to be Tasuke's forte, he's good with older CD mechanisms. He hasn't posted much here in a while, he's been fairly active at TH.
 

62vauxhall

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#18
Unfortunately, the limit switch seems OK. And also unfortunately, via the schematic, it is connected a Sony CXA-1082Q.

cxa1082b-sony-.jpg
Has anyone tried to re & re something like this? If any have had success, I'd be keen to know any helpful hints at disconnection and re-connection.
 
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