Need help with PSB Subsonic 5i

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jking519

Member
Joined 2017
I am having the same problem with my PSB 6i - it keeps blowing fuses. There doesn't appear to be anything burnt or blown on the boards, but I really don't have the knowledge to know for sure. I'm guessing it is do to this "glue" issue.

PSB want about almost $600 to replace plate amp.

Are there any other options for me to get this fixed other than doing my own soldering - since I don't have the knowledge?

Would a typical Electrical audio repair shop be able to do anything w/o knowing anything about PSB Subs?

Can I just purchase the BASH board (or whatever board is needed)?

What about a totally replacing with plate amp with some other brand? Would I be able to connect it to the driver?

TIA,
Joe
 
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dginqld

Member
Joined 2017
I am having the same problem with a PSB Subseries 1 that keeps blowing fuses. Have changed the mosfets and *unfortunately* identified the diac DB6 on the PDC board to be an issue (it is <1ohm both ways) but can't find anywhere that I can get one that doesn't involve buying 1000! Anyone know where I can get one? Thanks.
 
A

AshishJamesh

Member
Joined 2012
TonyH378 said:
Further to my previous tread, PSB Subsonic 5i Sub keeps blowing fuse, Jim Filaktakis has kindly sent me a copy of the service manual. Thank you, Jim.

After studying the manual for a while, I removed the amp from the cabinet. Apart from some corrosion on most of the boards, visual check didn’t reveal any obvious sings of burnt parts or tracks. After cleaning out the corrosion, I started to desolder components for out of board testing with a digital multimeter. The two power MosFets, Q401 & Q402, IRF730 x 2 (mine were IRF740) were found shorted. These were replaced. As there was no other obvious failing parts, I reconnected all the boards and give it a try. The fuse went again with a big spark!
Then I read an article about repairing a Subsonic 6. The author replaced all four power transistors and fixed the problem of fuse blowing. So this time I replaced the 2 IRF740’s together with Q200, IRF540 & D200, MUR420. Meanwhile, I would like to determine whether the SMPS itself or the Amp Board was causing the problem. So this time the SMPS was tested by itself. The retrial ended with another big spark!

Then another article caught my eye. This article pointed out the that the glue used on the BASS amp boards could became conductive after time and causing short circuit to parts. I cleaned up most of the glue and there was one big lump on the C438 sticking to the PDC1010 board. After cleaning up this lump of glue, there was a little bit of burnt residue of the glue, about 2mm in size, on the corner of the PDC, on the opposite side of the Diac. So I carefully desoldered the PDC out of the Main Board and cleaned up the area and had another good visual. No other burnt marks or parts could be seen. I then removed the Daic DB6 from the PDC and tested it with a DMM. Both sides measured >20m ohms and it was cleared of any fault. What a relief! I was so worried that it was a faulty Diac and it couldn’t be sourced anywhere after numerous search on the internet unless you buy 1000 pieces from the manufacturer.

Then I used an 8x magnifying glass to look closely at the components as there were so small. Then I noticed a hair line crack on the side of R4 (392 ohm). Out of board measurement was 200K ohm.
R5 & R6 tested alright. To be on the safe side, I replaced all 3, R4, 5 & 6. Resoldered everything back and reassemble the amp and tested it. Hurray!!! No more blowing fuse and it worked again!

After leaving the sub on low volume for about10 hours, I thought I might reset the Bias current. Following the instructions in the service manual step by step, I disconnect the control board cable from J6 and the driver wires from J102 and J101.Adjusted R714 & R 734 on the Linear PCB fully counter-clockwise. Connected a DC voltmeter to the bias header J103. Power on the amp. Checked initial meter reading which should be less than 1.3mV. Mine was reading 1.7mV. Then adjust R714 until the meter reads the initial value +0.3mV. Adjust R734 until the meter reads the initial value +0.6mV. Here is the problem. As I turned R714 or R734 clockwise, the reading started to go above 1.7mV instead of coming down. Any help from anyone regarding how to fix this problem would be greatly appreciated. The sub seemed to work alright with R714 & R734 set at fully counter clockwise position. Would this cause any damage to the amp?

Thank you guys.
Click to expand...

Hi have PSB Subsonic 6i sub in dead condition. I checked the components and I found Q401 & Q402 missing. And 220uf 50v Bipolar Capacitor missing. So these components cause my sub to get dead?
 
R

Rsmlabs

Member
Joined 2015
TonyH378 said:
Further to my previous tread, PSB Subsonic 5i Sub keeps blowing fuse, Jim Filaktakis has kindly sent me a copy of the service manual. Thank you, Jim.

After studying the manual for a while, I removed the amp from the cabinet. Apart from some corrosion on most of the boards, visual check didn’t reveal any obvious sings of burnt parts or tracks. After cleaning out the corrosion, I started to desolder components for out of board testing with a digital multimeter. The two power MosFets, Q401 & Q402, IRF730 x 2 (mine were IRF740) were found shorted. These were replaced. As there was no other obvious failing parts, I reconnected all the boards and give it a try. The fuse went again with a big spark!
Then I read an article about repairing a Subsonic 6. The author replaced all four power transistors and fixed the problem of fuse blowing. So this time I replaced the 2 IRF740’s together with Q200, IRF540 & D200, MUR420. Meanwhile, I would like to determine whether the SMPS itself or the Amp Board was causing the problem. So this time the SMPS was tested by itself. The retrial ended with another big spark!

Then another article caught my eye. This article pointed out the that the glue used on the BASS amp boards could became conductive after time and causing short circuit to parts. I cleaned up most of the glue and there was one big lump on the C438 sticking to the PDC1010 board. After cleaning up this lump of glue, there was a little bit of burnt residue of the glue, about 2mm in size, on the corner of the PDC, on the opposite side of the Diac. So I carefully desoldered the PDC out of the Main Board and cleaned up the area and had another good visual. No other burnt marks or parts could be seen. I then removed the Daic DB6 from the PDC and tested it with a DMM. Both sides measured >20m ohms and it was cleared of any fault. What a relief! I was so worried that it was a faulty Diac and it couldn’t be sourced anywhere after numerous search on the internet unless you buy 1000 pieces from the manufacturer.

Then I used an 8x magnifying glass to look closely at the components as there were so small. Then I noticed a hair line crack on the side of R4 (392 ohm). Out of board measurement was 200K ohm.
R5 & R6 tested alright. To be on the safe side, I replaced all 3, R4, 5 & 6. Resoldered everything back and reassemble the amp and tested it. Hurray!!! No more blowing fuse and it worked again!

After leaving the sub on low volume for about10 hours, I thought I might reset the Bias current. Following the instructions in the service manual step by step, I disconnect the control board cable from J6 and the driver wires from J102 and J101.Adjusted R714 & R 734 on the Linear PCB fully counter-clockwise. Connected a DC voltmeter to the bias header J103. Power on the amp. Checked initial meter reading which should be less than 1.3mV. Mine was reading 1.7mV. Then adjust R714 until the meter reads the initial value +0.3mV. Adjust R734 until the meter reads the initial value +0.6mV. Here is the problem. As I turned R714 or R734 clockwise, the reading started to go above 1.7mV instead of coming down. Any help from anyone regarding how to fix this problem would be greatly appreciated. The sub seemed to work alright with R714 & R734 set at fully counter clockwise position. Would this cause any damage to the amp?

Thank you guys.
Click to expand...
Hi TonyH378:

Great explanation!

Do you still have this service manual?

Thank you!
 
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