Quad 50e upgrade

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23-Sep-2018 01:16 PM

rafalow

rafalow

Posts: 61

I replaced the components on the Q50e pcb following the upgrade manual from the download page.

I now noticed that TR4 (replaced with BC560)  is extremely hot (over 100 degrees and going  higher).

who can help me to troubleshoot.


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24-Sep-2018 06:13 AM

rafalow

rafalow

Posts: 61

Thank you.

I used the BC560 following the manual.


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24-Sep-2018 06:51 AM

rafalow

rafalow

Posts: 61

tr5 and tr4 could be replaced by bc560 following the manual.

so I did.


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24-Sep-2018 07:09 AM

EJP

EJP

Posts: 1537

Sorry, I misread BC560 as BC550. It seems to me that BC557 would be better for its higher voltage tolerance.
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24-Sep-2018 06:21 PM

Ton

Ton

Posts: 37

Just trying to help...., in the 50D&E Operating Instructions Manual (download section),  T4 is a SGS BC 154 transistor. 

That one is still available: 

  BC154 silicon PNP transistor – SGS  

for only a few cents, so why go for a replacement, or am I missing something ?

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24-Sep-2018 07:37 PM

Ton

Ton

Posts: 37

oops... just noticed they have only one available.... :( 

but a few minutes google search revealed some more sellers...




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25-Sep-2018 02:33 AM

EJP

EJP

Posts: 1537

I'm wondering why you replaced it. If the old one was faulty and the new one overheats there must be an external cause. I would be checking the polarity of C7 and the value of R21 for a start, and Tr5 and Tr10, and checking the voltages at C, B, and E of Tr4 and Tr5.
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25-Sep-2018 06:24 AM

rafalow

rafalow

Posts: 61

I Upgraded because the previous owner has done some repairs with components with totally different values according the schematic.

so I replaced all components following the upgrade manual.

I could not find the original values and used some equivalent parts.

My fault I did not power on the amp before upgrading...and do not know if the problem already existed.

Tr4 and tr5 do not measure the same voltage. that I already noticed. 

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25-Sep-2018 06:58 AM

EJP

EJP

Posts: 1537

'Don't measure the same voltage' where? They have to be equal at the collectors, and different at the bases and the emitters. Whatare the voltages at these points?
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28-Sep-2018 05:39 AM

rafalow

rafalow

Posts: 61

TR4 and TR5 measure the same and voltage are oke.

I noticed that the extrem high temperatue involves the area of TR4.

R13,R22,and R23 are also extremely hot 100 degrees and climbing.

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28-Sep-2018 07:13 AM

EJP

EJP

Posts: 1537

I repeat. Tr4 and Tr5 cannot possibly measure the same voltage except at their collectors. I'm trying to help but you need to answer the questions I ask, and 'OK' isn't an answer to 'what are the voltages at these three points?'

However I suggest you have the upper side biased too high. You need 30-40mA through each side of the output transformer, which as mentioned in the upgrade manual corresponds to 15-20mV across each of R30 and R31. Or C7 or C8 are back to front.

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29-Sep-2018 11:48 AM

rafalow

rafalow

Posts: 61

ejp

I am sorry, i was in a bit of a hurry when i wrote the reply.

TR5  cb = -10,7v / be=0,64v / ce=11,3v

TR4  cb= -10,7v / be=0,6v / ce=11,3v

hope this helps.!

I will take a look at R30 and R31 again  but i am pretty sure they are at 20 mv across each

kind regards

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15-Oct-2018 12:49 PM

rafalow

rafalow

Posts: 61

I checked  the  30-40mA through each side of the output transformer, which as mentioned in the upgrade manual  and it  corresponds to 15-20mV across each of R30 and R31

I noticed that MR 10,11,12,13 are removed and replaced by a MB256,   and I measure +41v  dc behind MB256.

can this be the problem..?


kind regards


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16-Oct-2018 01:24 AM

EJP

EJP

Posts: 1537

Not really, as long as you still have about 20V on the left side of Tr11 as per schematic. Your voltages around Tr4/5 look OK too. I would double-check all your soldering for dry joints and accidental solder bridges.
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