Salas hotrodded blue DCB1 build

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
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ghiglie said:
Well, it took a month but... unsoldered the IRFP, tested and it is still good. I put it back on the PCB, redid my measurements - 0,8mV/2,0mV , I wish I could do better but I can't notice the difference but I still feel the pain of desoldering small components.
My next question: PCB solder squares are on the "unmarked" side, right? 'Cause I blew one and got away from it.. :(
Click to expand...
The LEDS squares and rounds are connected on the flip side, yes. On top where the parts are, they just double up.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
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ghiglie said:
but I still feel the pain of desoldering small components.
Click to expand...

Solder wick and bit of tacky flux are your friends for rework, use the iron gently. There are also very cheap desolder pumps with hollow iron nozzle. Mains powered. They need some maintenance work soon, like cleaning the shaft's coil and greasing the rubber seals, but for few reworks here and then they are helpful. Manually actuated they cost something like 12 Euro online.
 
S

Scorpion

Member
Joined 2002
Hi Salas,

I am well advanced in my DCB1 resistor tryouts and only one resistor remain to be chosen (the 220R at the output). Will post a lot of results in the next days.

Still in the meantime, I decided to remove the "test board" and install the "final board" (more closely matched, better relay, tiny resistor differences)...but I do have some problems that I can't solve with my minimal technical knowledge. ..

Positive IRFP9240 channel is working perfectly with:
9,98v LED quintet
0.97v LED triplet
1,35 Vdrop
0,35 DC Offset

On the negative IRFP240 channel: nothing, niete, nada !!!

I do have a "short" somewhere as that is what I measure on the PSU (on the 4700uF lytics)....well in fact, I have some 18volts for less than a second...and than a "short". Also when I first power up the board, the LED quintet on the negative channel light up for 1-2 secondes and then quickly fade away to complete OFF. The LED triplet never turns ON (I have checked ALL LEDS individually- twice- and they all work and are properly oriented).

Also, the very first time I powered up the board, I left it ON for some 10-15 minutes or so (even if the left channel wasn't working at all) while taking measurements on the positive IRFP9240 channel. ..BUT then, some smoke started to come out of the voltage rectifier L7812ACV wich sports a heatsink. ..

Btw, the relay clicks everytime and seem to be working just fine.

I have no idea where to start. I thought the rectifier diodes might be the culprit (since I have a "short" at the PSU level) but, if so, why the LED quintet is able to turn on, even for a seconde or two?

I don't know. Could the IRFP240 and/or the 2SK170BL closest to the triplets be involved? Or the IXYS 15A 1200v rectifier diodes?

Also, would it be safer to order a new L7812ACV voltage rectifier and change it (just to be on the safe side) since smoke came out of it twice...

Please help me get this thing going.

Thanks a lot

Sincere regards
Scorpion
 
Last edited:
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
First make sure that you did not wire the transformer secondary somehow that it gave too much voltage to the negative polarity half. Do you use fuses on the transformers? Look if one is gone. Check the rectifiers with the diode function on a DMM.
 
S

Scorpion

Member
Joined 2002
Salas said:
First make sure that you did not wire the transformer secondary somehow that it gave too much voltage to the negative polarity half. Do you use fuses on the transformers? Look if one is gone. Check the rectifiers with the diode function on a DMM.
Click to expand...

Hi Salas,

Thanks for the usual quick answer.

Updates:

●The voltage on the secondaries is around 15.9v both for the positive and negative side (That I had already checked before).
●I do use fuses in my DCB1 but I am testing the "final board" outside (without fuses). Same way I did it for the 1st board.
●All 4 rectifiers have the same voltage of some 19.5v BUTone the rectifiers from the defective negative channel (the one nearest to the side) alternates constantly between "short" and full voltage 2-3 times per seconde
● The voltage rectifier L7812ACV remains incredibly HOT to the touch even though I took the opportunity to change the CCS resistors from 1.2R to 30R in order to lower demand while testing


It seems the IXYS diode is the culprit or, at least, might be part of the problem, no?

What about the almost "boiling" L7812ACV? Seems defective also? Do I need to change it as well?

Thanks for the follow up

Regards
Scorpion
 
S

Scorpion

Member
Joined 2002
BigE said:
Twice? It is very likely gone after the first time.
Click to expand...

Hi BigE,

How are you doing?

Yep, what I thought as well but a friend keeps telling me nope over and over (cause they would have some kind of heat protection and what not).

I will change it anyway just to be on the safe side. But why o why it became soooooo hot?

Take care

Regards
Scorpion

BTW: Off topic but I am sad you guys didn't get the 1st overall pick for Connor McDavid...It would have boosted the rivalry MTL-TO back to the good old days...Why Edmonton. ...again !?!?
 
S

Scorpion

Member
Joined 2002
Salas said:
That diode is the most suspicious one. You may be boiling the 7812 with excessive ripple. Check the diodes when the power is off with a DMM in diode test mode. Has a diode symbol around the dial.
Click to expand...


Hi Salas,

I changed both the defective diode and the overheated L7812. Now I do have equal voltage on both channel's PSU and the 7812 doesn't get hot anymore... still all LEDS from the IRFP240 (negative) channel refuse to light up...even if I tested them twice for correct orientation and to see if they were all working, which they do.

What's next suspect? One of the MOSFET? The LSK170BL nearest to the triplets?

Please advise.

Thanks a lot

Regards
Scorpion
 
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