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Old 21st June 2004, 04:54 AM   #1
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Default Sony 5.1 output transistors repair

I am now working on my little brother's Sony 5.1 receiver (after I have some confidence after having just repaired my Mom's Marantz 6.1 receiver with this forum's help), I found that both transistors on his right channel were dead and am now looking for the cheapest distributor of these parts. Anyone know where I can find a Sanken MN2488 and Sanken MP1620 for cheap with cheap shipping? Thanks.
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Old 13th August 2004, 03:08 PM   #2
rkc7 is offline rkc7  United States
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I bought some off of Ebay from a distributor named "Activeparts." They were like $8 per pair plus $5 shipping... cheapest I've found. Auction .

And I replaced them in a Sony receiver I have and they seem to work fine. Also, make sure you check emitter resistors and the various resistors on the board. On mine half of the dual-emitter resistor on the channel needing new transistors was blown and a 680ohm resistor around the transistors was blown.... there was also a 10ohm resistor around the middle of the board which looks to have been replaced (well, actually just bypassed with another 10ohm resistor) when I bought it broken off of Ebay. Good luck!
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Old 13th August 2004, 08:40 PM   #3
jaycee is offline jaycee  United Kingdom
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Just to help you out, I found this:

"I ordered MN2488-OPY-M and MP1620-OPY-M transistors from Sony and got 2SD2488 and 2SB1620 as substitutes."

Apparently, the MN2488 and MP1620 were just rebranded SD2488 and 2SB1620 transistors, perhaps specifically matched for Sony. They are apparently now discontinued but transistors with the same spec should work fine.
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Old 14th August 2004, 01:48 PM   #4
anatech is offline anatech  Canada
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jaycee is right on. I have repaired several Sony receivers over the years using the real numbered parts. I was just about to mention this when I read jaycee's post.
I've said this before, buy your parts from reputable distributors only! The difference in cost, if there is, is never worth more than having the thing blow up again due to rebranded fake parts. Try to use original numbers (or exact factory parts), ECG's, NTE's or whatever are your last choice!!! If you must cross reference, use original data books only. Do not trust replacement brand sub books.
-Chris
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Old 16th November 2004, 05:37 PM   #5
macboy is offline macboy  Canada
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Quote:
you must cross reference, use original data books only. Do not trust replacement brand sub books.
Good point. I usually consider substitutions listed in cross-reference books to be valid only during design of a new circuit (where you can account for different gain, SOA, thermal requirements, etc.), not for straight replacement in an existing design. And even then you absolutely must check the manufacturer's datasheets carefully to make sure that the device suits your needs.

Unfortunately, the MN2488 and MP1620 are discontinued and not easy to find. They are not typical power transistors, they are darlingtons, and they have a fairly unique combination of voltage, current and power ratings. That makes them virtually impossible to substitute. Their popularity, especially with Sony, and their failure rate means a pretty consistent demand for replacements. That demand coupled with discontinued status means that fakes will likely be on the market.
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Old 16th December 2005, 09:40 AM   #6
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Default Cheap MN2488 MP1620

This is the supplier I used in the UK

Cheap and fast service

http://www.dalbani.co.uk/index.php
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Old 7th June 2008, 07:34 PM   #7
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it seems that national semiconductor is suggesting to use these in AN-1490... Anybody knows where to find a darlington with a transition frequency of 55MHz and capable of dissipating 150W?
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Old 7th June 2008, 08:45 PM   #8
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Quote:
Originally posted by jaycee
Just to help you out, I found this:

"I ordered MN2488-OPY-M and MP1620-OPY-M transistors from Sony and got 2SD2488 and 2SB1620 as substitutes."

Apparently, the MN2488 and MP1620 were just rebranded SD2488 and 2SB1620 transistors, perhaps specifically matched for Sony. They are apparently now discontinued but transistors with the same spec should work fine.

Be careful if using new transistors of a different type.
You will probably have to reset the bias level.
I use a scope and sig gen but many people just use a multimeter.
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Old 7th June 2008, 09:08 PM   #9
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Question: Are these transistors sonically-speaking as wonderful as on paper?
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Old 8th June 2008, 05:22 AM   #10
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Yes, they're sonically very good, especially for darlingtons. They're very fast and have reasonable SOA. Darlingtons in a Class-AB/B Emitter Follower have a relatively small Vbe-biasing sweet spot, and Sony apparently uses a carefully-controlled Sziklai Vbe multiplier with a hi-beta (>1000) master to achieve this. The rest of the stuff is usually in a monolithic analog LSI.

I'm not sure if they'll sound just as good in an all-discrete implementation without careful optimization, but at the time they were manufactured for Sony, it was probably a very optimal value-engineered design choice. The alternatives like the TIP142/147 sound much worse in similar topologies.
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