I was just desoldering Q3, when I fipped and made a picture of the underside, focusing on the section that can cause trouble:
http://i49.tinypic.com/2e5uo2x.jpg
Nevermind those dirty holes in the middle I'll wipe them clean.
http://i49.tinypic.com/2e5uo2x.jpg
Nevermind those dirty holes in the middle I'll wipe them clean.
I see a solder plot at the right bottom of the pic, seems to make short between gates and ground plane
otherwise solders look OK.
nAr
Removed the blob. Desoldered Q1, and that place between too pins looks supicious. I tried to clean, as much as possible to show.
http://i47.tinypic.com/mvg5f7.jpg
Can there be short going on? I think the "line" should be separating two pads, as far as I can see on the other board. How can I clean it properly? I'm afraid to use blade here, when not knowing what is underneath.
http://i47.tinypic.com/mvg5f7.jpg
Can there be short going on? I think the "line" should be separating two pads, as far as I can see on the other board. How can I clean it properly? I'm afraid to use blade here, when not knowing what is underneath.
I don't think there is short here. Work seems nicely done except some component leads not cut short enough sometimes maybe
Not a big deal though.I would like to help more, but my box for Pearl is closed and I can't go and see reference voltages. I'l trying to get an annotated sheet with voltages, I had it somewhere but I can't find it for now
maybe it is attached to the thread Best,
nAr
EDIT : found ... attached
Compare to your voltages and debug what is faulty.
As I said 8V - 10V on the jfet drains Q6 - Q9 is fine for biaising. For this, first the sub regulator Q1 and the cascode Q3 must behave correctly.
I had a 8,93V reading on my boards, whilst author of pdf finds 9,4V. Both values are within OK range.
If Emiter of Q3 is 9,4V, then Base must be 10V or so. Collector of Q3 is about 10V1, the cascode is roughly polarized to half the supply rail (a little less, in fact half the Emiter voltage of subregulator Q1).
Emiter of Q1 about 20,2V so Q1 Base is about 20,8V. 24 - 20,8 = 3,2V on R5, which gives 3,2/1500= 0,00213333 A so about 2,13 mA current.
Last edited:
Thank you, Anaël. You, guys, are already a big help. Yes, I check measurements with Wayne's ones. Yesterday night I've changed Q1 and it fixed some of voltages for sure. New Q1 on other board has been installed just right now. I'm rewiring boards to have some "ordnung" now.
It's a national day off here. That helps a lot. Will I celebrate our kings day with some Pearl music, only ancient gods can tell.
It's a national day off here. That helps a lot. Will I celebrate our kings day with some Pearl music, only ancient gods can tell.
I don't think there is short here. Work seems nicely done except some component leads not cut short enough sometimes maybe
I would like to help more, but my box for Pearl is closed and I can't go and see reference voltages. I'l trying to get an annotated sheet with voltages, I had it somewhere but I can't find it for now
Best,
nAr
EDIT : found ... attached
Compare to your voltages and debug what is faulty.
As I said 8V - 10V on the jfet drains Q6 - Q9 is fine for biaising. For this, first the sub regulator Q1 and the cascode Q3 must behave correctly.
I had a 8,93V reading on my boards, whilst author of pdf finds 9,4V. Both values are within OK range.
If Emiter of Q3 is 9,4V, then Base must be 10V or so. Collector of Q3 is about 10V1, the cascode is roughly polarized to half the supply rail (a little less, in fact half the Emiter voltage of subregulator Q1).
Emiter of Q1 about 20,2V so Q1 Base is about 20,8V. 24 - 20,8 = 3,2V on R5, which gives 3,2/1500= 0,00213333 A so about 2,13 mA current.
Mind the error; -26,2V; in the voltage written taken at node of R25 & R27.
Since Emiters are at about -23V, the Bases of bipolars should be standing around -22,4V. This voltage is seen on R25 referenced to Ground, or a current of about 4,71mA through R35 (and also through red led, assuming 1,6V (1V R + 0,6V BE junction) direct voltage for the led @ said current).
Best,
nAr
Thanks for detailing and pointing it out. I'm using this corrected sheet:
http://www.diyaudio.com/forums/attachments/pass-labs/253484d1323200010-pearl-two-pearl2votages1.pdf
I've left home for home town and celebration. Just after replacing Q1, I only had time for Q1 and Q3 measurements:
Q1
C 24V; 24V;
B 20.7V; 20.7V
E 20V; 20V;
Q3
C 06.7V; 06.7V
B 07.3V; 07.3V
E 06.7V; 06.7V
Getting back to it soon.
http://www.diyaudio.com/forums/attachments/pass-labs/253484d1323200010-pearl-two-pearl2votages1.pdf
I've left home for home town and celebration. Just after replacing Q1, I only had time for Q1 and Q3 measurements:
Q1
C 24V; 24V;
B 20.7V; 20.7V
E 20V; 20V;
Q3
C 06.7V; 06.7V
B 07.3V; 07.3V
E 06.7V; 06.7V
Getting back to it soon.
Sorry, I was off too try this last update to my posts ...
nAr
Yes, seems definitely better. Q1 seems to behave perfectly. Voltage on Collector, Base and Emiter of Q3 still seem off.
My friend PierreQuiRoule had the same problem if I recall.
That can be tweaked by modding a R value ...
EDIT : Done. Can you try changing R9 for 333 ohms or so, and report Q3 voltages again.
If you don't have a 330 or 333 ohm ready, just solder a 1k in parallel of existing 499
Best,
nAr
try this last update to my posts ...nAr
Yes, seems definitely better. Q1 seems to behave perfectly. Voltage on Collector, Base and Emiter of Q3 still seem off.
My friend PierreQuiRoule had the same problem if I recall.
That can be tweaked by modding a R value ...
EDIT : Done. Can you try changing R9 for 333 ohms or so, and report Q3 voltages again.
If you don't have a 330 or 333 ohm ready, just solder a 1k in parallel of existing 499
Best,
nAr
Moderator should erase my post 1578.
Please refer to post 1579 for trying something valuable
Best,
nAr