Pioneer QX-949A in protection, one channel high VR 3/4 voltage.
- Thread starter Nashou66
- Start date
-
- Tags
- protection relay qx-949a
Anyone on this? I think I'll leave them as they measure fine. The ESR is 16 ohms, I thought that was high but a search on new tantalums of the same value come up
about the same ESR. So I guess there must be a reason they use a high ear cap there, right?
Nashou
Well no go, put amp module back in fired it up and no go. Saw some slight smoke from some where. So I have to pull the module back out and start checking part.
The heat sink got hot fast and I had the unit plugged into a power monitor and that went up to 800 watts!! SO something is a miss. I only had it on for a few seconds.
Might have been enough to do more damage but I think the outputs are ok, they all measure the same on both halves .
Nashou
The heat sink got hot fast and I had the unit plugged into a power monitor and that went up to 800 watts!! SO something is a miss. I only had it on for a few seconds.
Might have been enough to do more damage but I think the outputs are ok, they all measure the same on both halves .
Nashou
UncleBingo
Super Member
Did you verify the pinouts on the new transistors? Check datasheets on the oId transistor's numbers against the pinout of the new transistor's They aren't aIways the same
UncleBingo
Super Member
Have you buiIt a dim-buIb tester? If not, stop everything and do so
It keeps the residuaI damage from driving you insane
It keeps the residuaI damage from driving you insane
Yeah I need to make one. I have had luck so far not using one on other repairs.
But will do so tomorrow.
Nashou
Pretty sure I did.
But after I pull it out I'll check it again. on the emitter of the replacement transistor for the 1451 was 12 v should be 1.2 . So I have to double check.
Nashou
UncleBingo
Super Member
KSC3503 is ECB the 1451 is EBC
Ummm , ummm well I was correct on that transistor but wrong on the KSA726 , Replaced by KSA992's, One of them was wrong (Q2 pointed to in picture)! ugh
I removed it and its complimentary and they both measured fine. My Hakko 805 clogged up so After I clean it I'll check the 2SC869 ( Q6) replacement
to see if that go damaged. Well I better check all parts around that transistor i guess cause there was some slight smoke and forgot to mention a buzzing sound, very faint.
EDIT: Well Q2,Q4, and Q6 all are ok. Not sure what else to check, I guess all transistors. and that was in the channel that was good, I think thats a rear channel.
Checked the output transistors and they all measure ok on my tester while in circuit.
Good news!!! The relay clicked and pin 4 now measures 9.6 mV's and pin 22 ( side i had TR in wrong) is 13mV's as well.
The wattage draw was about 54 watts, much better than the 800 plus during my eff up !!
So now onto the other amp board for a full overhaul and then onto he pre amp board. Not looking forward to removing that
from the front face plate.
Athanasios
The wattage draw was about 54 watts, much better than the 800 plus during my eff up !!
So now onto the other amp board for a full overhaul and then onto he pre amp board. Not looking forward to removing that
from the front face plate.
Athanasios
Ok , I'm on the pre amp tone board and have a question again about the blue dry tantalum caps on that board. I did not replace them on the amp board.
But I remember reading somewhere that on the pre amp board they should be changed but cant find it.
I read also somewhere also that they have a high ESR for a reason in a circuit to prevent oscillation of certain circuits.
So what have others done here?
Nashou
But I remember reading somewhere that on the pre amp board they should be changed but cant find it.
I read also somewhere also that they have a high ESR for a reason in a circuit to prevent oscillation of certain circuits.
So what have others done here?
Nashou
Ok, will do.
there are four 2.2 uf blue drops there, but I only have 3.3 uf on hand, would that be ok to use there? I think it be ok , but like to hear another opinion.
I can order some but I want to get this off my bench this weekend and don't feel like waiting
Nashou
< 4.0uf, use Film caps. Cornell Dublier DME Series and the WIMA MKP/MKS are good choices. Size is a concern so use the smallest physical size replacement. Get rid of the 'Tants.