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Old 31st January 2013, 10:05 PM   #21
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Ok....chop chop time....some work done today:

All aparently bad components removed...capacitors only removed to clean the board better...and they have the plastic burned...so new ones...

Click the image to open in full size.

Left Side cleaned:
Click the image to open in full size.

Right side cleaned:
Click the image to open in full size.

What do you think? ready to apply araldite?
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Old 1st February 2013, 12:43 AM   #22
jaycee is offline jaycee  United Kingdom
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Good.. the left side damage is not too bad. Unfortunately the right side is, but I'm sure it can be salvaged.

That TIP2955 looks suspicious to me... the ST logo does not look right. I'd say it was a fake (though why anyone would fake a 2955 is beyond me!). ST have certainly never made them in that package style - older ones were TO-218 (as the TIP3055 is) and modern ones are TO-247 style.

The amp does have all the signs of either having been run into a short, or run excessively loaded which caused output device failure.
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Old 1st February 2013, 12:53 AM   #23
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Those are similar to the ones I have here.
ST never seemed to label their transistors two batches alike.

But nice job with the "sunny side". How about the essential one?
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Old 1st February 2013, 01:42 AM   #24
jaycee is offline jaycee  United Kingdom
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From looking at the circuit board, it looks like Q11/Q12 and Q111/Q112 have been replaced with the wrong devices - looks like BC546/556 have been used. Evidently these transistors failed and when the guy who did the repair couldnt find FST239/240, he decided to use those.

They are not up to the job unfortunately. ZTX653/753 is the correct replacement.
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Old 1st February 2013, 09:37 AM   #25
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Quote:
Originally Posted by jaycee View Post
Good.. the left side damage is not too bad. Unfortunately the right side is, but I'm sure it can be salvaged.

That TIP2955 looks suspicious to me... the ST logo does not look right. I'd say it was a fake (though why anyone would fake a 2955 is beyond me!). ST have certainly never made them in that package style - older ones were TO-218 (as the TIP3055 is) and modern ones are TO-247 style.

The amp does have all the signs of either having been run into a short, or run excessively loaded which caused output device failure.
Yeah looks a little suspicious to me too....:S
I take them all out...take a look at this pic:

Click the image to open in full size.

Quote:
Originally Posted by TANDBERGEREN View Post
Those are similar to the ones I have here.
ST never seemed to label their transistors two batches alike.

But nice job with the "sunny side". How about the essential one?
The circuit side it's ok...the only spot that need to do some circuit repair is te one that have a hole...i will take a photo before repair with Araldit because now i put some tape to do a base for fill with the glue...will post a pic late today...

Quote:
Originally Posted by jaycee View Post
From looking at the circuit board, it looks like Q11/Q12 and Q111/Q112 have been replaced with the wrong devices - looks like BC546/556 have been used. Evidently these transistors failed and when the guy who did the repair couldnt find FST239/240, he decided to use those.

They are not up to the job unfortunately. ZTX653/753 is the correct replacement.
As soon as i get home i will check this components...but yes...they look different from the other transistors on this amp...the side that have letters are grey...this is what take my attention....i will take a look too see if the solder are intact or not.....
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Old 1st February 2013, 01:15 PM   #26
jaycee is offline jaycee  United Kingdom
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I could be wrong and the TIP2955 are genuine, but I cant find any ST datasheet that shows that they made them in a TO-3P package - only the original TO-218 package, and now the more modern TO-247 package. The only versions of them I can find that were made this way, are Chinese copies which are probably inferior quality.

Anyway, they should both have been replaced, IMO. As the repair attempt appears to have failed, I would replace both sets of transistors again to be certain that they are not faulty.

The original Q(1)11/Q(1)12 should look much like Q7/Q107 does. This is called the E-Line package. If you can't get the ZTX653/753, I would say BC639/640 could work - but they have a different pinout, so you will have to bend the leads to fit in the right place.
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Old 1st February 2013, 01:21 PM   #27
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C16 looks pretty roasted. I would change ALL the electrolytics on BOTH channels.

Change the faulty channel first though as you may need the undamaged channel for fault finding.

These ST devices are all genuine....
Attached Images
File Type: jpg DSIR9523.JPG (234.0 KB, 53 views)

Last edited by KatieandDad; 1st February 2013 at 01:46 PM.
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Old 1st February 2013, 02:17 PM   #28
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Ok...so i do a "short list" and will play safe and replace the following components:

FUSES:
2x FUSE 2A/250v
1x FUSE 630ma T
----------------------------------------
LEFT SIDE:
Q13 -> TIP3055 (TO-218) or (TO-247)
Q14 -> TIP2955 (TO-218) or (TO-247)
---------------
R28
R35
R37
R38
R39
R40
---------------
D1
---------------
C14
C15
C16
---------------
FST239/240 replacement-> ZTX653/753
Q12
Q11
---------------
RV1 -> Iskra 1k
----------------------------------------
RIGHT SIDE:
Q113 -> TIP3055 (TO-218) or (TO-247)
Q114 -> TIP2955 (TO-218) or (TO-247)
---------------
R128
R135
R137
R138
R139
R140
---------------
D101
---------------
C114
C115
C116
---------------
FST239/240 replacement-> ZTX653/753
Q112
Q111
---------------
RV101 -> Iskra 1k
----------------------------------------

I think i don't forgot anything.....and correct me if i'm wrong...

Regarding the C14/C114 the original one it's a little different capacitor...do you guys know the original brand from the one int the left side?
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Old 1st February 2013, 02:23 PM   #29
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The components are so cheap so I would say yes. Change the lot.

You could change the cooked bits only to miss one failed component only to have to change them all again.

You can of course take everything out and test every last component. It's labour intensive but at least you will know that everything is OK.

Caps are difficult to test so change them anyway.

Last edited by KatieandDad; 1st February 2013 at 02:25 PM.
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Old 1st February 2013, 06:34 PM   #30
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Q(1)11/Q(1)12 already removed...look what was there:

https://www.dropbox.com/s/22chnnv0gf...2018.17.15.jpg

Last edited by CrustyD3mon; 1st February 2013 at 06:39 PM.
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