Output transistors for Marantz 250M

UrbaXter

UrbaXter

New Member
Hi guys, I burned out the right channel output transistors of my 250M... :(
According with the SM the right ones are SJ2519 and SJ2520, BUT, my unit has at the left channel, two pairs of A747A and C1116A, so my questions are:

1- We have today options available for the originals?
2- I found here in my country people selling NOS of the ones in left channel, should I buy them?

Thank you so much in advance! :)
 
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Try DigiKey for output transistors by Onsemi. There are some counterfeit transistors out there so be careful.
 
homebrew said:
Try DigiKey for output transistors by Onsemi. There are some counterfeit transistors out there so be careful.
Click to expand...

Thank you for the answer homebrew!

Sorry, I'm a newbee... I did a search on DigiKey but shows 0 result :(
There's another way to find a substitute for these transistors?
 
Well Urba, if Digi Key doesn't have them, your next bet would be eBay. Look for original Motorola, or Sanken and OnSemi substitutes. Beware counterfeits!
In my searches, it looks like these transistors won't be easy to find.
 
MJ21193G/195G
MJ21194G/196G
Have almost the same specs.....Compare the sheets yourself.
 
Hey guys, Thank you so much for the info and links! :)

The question is, should I go for these OnSemi options in both channels (four pairs), or better buy these I already found on Ebay (two pairs) that are same as the installed in the left channel? (See the image)
Any guesses?

transistors_250M_left_right_P_2.jpg
 
avionic said:
Buy new from a known legit source.. EBAY is like a box of chocolates:thumbsdown:
Click to expand...

Like a box of chocolates filled with potential smoke.
Will a full power test run or will I destroy an entire channel due to counterfeit transistors? Spin the wheel and find out!
 
Well, maybe I'm wrong, but seems not to be so hard see what are trustable or not on Ebay, some with a very "shiny metal" from China for sure are fake, but other sellers with 99% positive reviews and from USA seems more reliable, am I wrong?
Look this for an example: https://www.ebay.com/itm/282349057261
 
Go with avionic's suggestion for replacements. Looking at your photo it seems to me that the right channel transistors are definitely not OEM. I can't really tell but it looks like the "burned" transistors are each a different transistor replacement. The recommended MJ21193/94 transistors are excellent but I have a feeling there is something seriously wrong with the right channel of this unit that needs correction first. Just replacing the old burned transistors with the new ones will destroy the new ones without resolving the underlying issues first. If the left channel is working properly I would not replace the originals devices at this point. The "good" board can be used as a reference if needed during repairs of the left.
 
Thank you guys, again for the comments...Well, this is the short history, I purchased this 250M about 10 years ago, it was working and very good looking outside but very rusty inside, so I decided to disassemble and clean up everything, but unfortunately, when I mounted it, I did not realized and pressed a couple of wires under the transformer... As that time I had no idea what was a DBT, yes, it smoked... :(

After all the work, of course, I felt very disappointed and left it on the shelf all this time.

Now I already replaced the damaged wires, and "fixed" the relay that burned one (not on circuit) leg, but is working... beyond this I only found these output transistors burned.
I'm really convinced that the avionic's suggestion is the best option, I will post the result here in the case in the future this could help another 250M owner. :)
 
UrbaXter said:
Thank you guys, again for the comments...Well, this is the short history, I purchased this 250M about 10 years ago, it was working and very good looking outside but very rusty inside, so I decided to disassemble and clean up everything, but unfortunately, when I mounted it, I did not realized and pressed a couple of wires under the transformer... As that time I had no idea what was a DBT, yes, it smoked... :(

After all the work, of course, I felt very disappointed and left it on the shelf all this time.

Now I already replaced the damaged wires, and "fixed" the relay that burned one (not on circuit) leg, but is working... beyond this I only found these output transistors burned.
I'm really convinced that the avionic's suggestion is the best option, I will post the result here in the case in the future this could help another 250M owner. :)
Click to expand...
Nice amp, had one once. We all eff things up once in a while, get this baby up and playing your tunes again. :thumbsup:
 
UrbaXter said:
Thank you guys, again for the comments...Well, this is the short history, I purchased this 250M about 10 years ago, it was working and very good looking outside but very rusty inside, so I decided to disassemble and clean up everything, but unfortunately, when I mounted it, I did not realized and pressed a couple of wires under the transformer... As that time I had no idea what was a DBT, yes, it smoked... :(

After all the work, of course, I felt very disappointed and left it on the shelf all this time.

Now I already replaced the damaged wires, and "fixed" the relay that burned one (not on circuit) leg, but is working... beyond this I only found these output transistors burned.
I'm really convinced that the avionic's suggestion is the best option, I will post the result here in the case in the future this could help another 250M owner. :)
Click to expand...

:thumbsup:
 
Hey guys, so here´s a quick update... I installed the new ON output transistors, but unfortunately, seems that something more is in short at the right channel... :(
When I turn on, the bulb of the DBT brights high, dim a bit, but still keeps the bright of about 70% and the relay does not click. If I disconnect the right and keep only the left and good channel, the bulb dim almost totally and the relay clicks.
I had tested before the transistors, on board with a multimeter, but did not find any short, so do you guys have any hint about what could still wrong?

Stupid Question: I was a bit confused about the position of the transistors at the heatsink, the two boards seems inverted but not mirrored, so as in the left channel, I installed the two PNPs (MJ21193) at the top and the NPNs (MJ21194) at the bottom, but as at the right side the heatsink need to be up side down, after mounted the transistors are inverted, is that right, no? (See image attached)

IMG_20220201_232523232.jpg IMG_20220203_000419466.jpg
 

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Another quick update for who are interested to know the "happy" end of the history... I checked the voltages and noticed that the case/collector of the output transistors were with 55v instead of zero expected, and the cause of this were two burnt transistors R529 and R530, I replaced them and voilá... the monster is alive again!
I checked DC offset, set the bias at 12.5mv, and spent all the weekend enjoying my music... The 250M worked smoothly and sounds reaaaallly good! :)
IMG_20220218_012146387_HDR.jpg IMG_20220218_123952523_HDR.jpg
 
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