Just wondering how other people in this group buy are getting on with their builds.
I've finally completed the power supply (as well as the misc boards).
Spent the past 2 hours tracing a short to C235 (0.1u) that took out V232 on the positive rail. Amazingly, Mouser had accidentally sent me 2 of those Fets instead of one, so no waiting for a minimum order for that one!
Power supply is now rock solid on both rails and all that's left is the amp board and probably copious amounts of troubleshooting!
I've finally completed the power supply (as well as the misc boards).
Spent the past 2 hours tracing a short to C235 (0.1u) that took out V232 on the positive rail. Amazingly, Mouser had accidentally sent me 2 of those Fets instead of one, so no waiting for a minimum order for that one!
Power supply is now rock solid on both rails and all that's left is the amp board and probably copious amounts of troubleshooting!
If I find I missed ordering something/broke something I usually get it from RS (free delivery no min order) or Arrow (free express delivery, no min order, and you can usually find discount coupons floating around the place).
Just wondering how other people in this group buy are getting on with their builds.
I've finally completed the power supply (as well as the misc boards).
Spent the past 2 hours tracing a short to C235 (0.1u) that took out V232 on the positive rail. Amazingly, Mouser had accidentally sent me 2 of those Fets instead of one, so no waiting for a minimum order for that one!
Power supply is now rock solid on both rails and all that's left is the amp board and probably copious amounts of troubleshooting!
well with arrow you can pay by paypal avoiding intl txn fee, otherwise can look into something like a 28degrees credit card which has no intl fees.
rs do sometimes ship from the UK though which ends up taking about a week or a week and a bit, but for next day delivery items they really do next day courier it!
rs do sometimes ship from the UK though which ends up taking about a week or a week and a bit, but for next day delivery items they really do next day courier it!
Thanks X. I'll also try not to let any of those little SMD critters escape!
I ended up mounting the voltage regulators onto a remote bracket as the orientation of one of the reg PCBs wasn't compatible with the vertical back to back heatsink arrangement. Otherwise, everything has fit together real nicely.
I ended up mounting the voltage regulators onto a remote bracket as the orientation of one of the reg PCBs wasn't compatible with the vertical back to back heatsink arrangement. Otherwise, everything has fit together real nicely.
Amp board build was straightforward as you mentioned, X, but things haven't quite gone to plan.
Somehow, when making the molex jumper from the PSU to AMP, this dummy managed to switch the +18v and -18v lines.....
Consequently I've put reverse voltage down both rails and needless to say, the amp does not work when properly energised. The voltage on the rails starts to rise a few volts before being cut off by the bench supply.
At least the power supply side survived intact - I still get +/- 18v, and there was no smoke..
I'm pretty p***ed with myself for making such a stupid error (don't work late at night), and my brain is now pretty fried trying to find the initial fault.
I'd be grateful for any pointers as to which components should be first up in testing so I can quickly sort this mess out and pretend that I didn't screw up...
Thanks!
Somehow, when making the molex jumper from the PSU to AMP, this dummy managed to switch the +18v and -18v lines.....
Consequently I've put reverse voltage down both rails and needless to say, the amp does not work when properly energised. The voltage on the rails starts to rise a few volts before being cut off by the bench supply.
At least the power supply side survived intact - I still get +/- 18v, and there was no smoke..
I'm pretty p***ed with myself for making such a stupid error (don't work late at night), and my brain is now pretty fried trying to find the initial fault.
I'd be grateful for any pointers as to which components should be first up in testing so I can quickly sort this mess out and pretend that I didn't screw up...
Thanks!
Sorry to hear that Avtech. I know how that feels...
I have done this at least 4 times (maybe more) in my amp building lifetime. Don't feel too bad. The worst was connecting a 250VA 25v toroidal trafo to an amp via a CRC and no fuses present anywhere. The trafo hummed and smoke appeared on wires from CRC to amp and wire insulation melted and wires fused together. The R's in the CRC's finally served as the fuse and went open about the same time that I pulled the plug. Miraculously, the amp itself was unhurt - as the current just shunted across the reverse biased MOSFETs like a dead short. I had to replace the R's on the CRC and all the wiring.
Did you see or smell smoke on the main amp board when this happened? The fact that the PSU is still good is a great sign because that means you did not put more than 310mA of current into the amp. Those are TO220 P-channel MOSFETs. When reverse biased, they generally conduct like a diode and don't get damaged. They can handle many amps of current so 310mA is no problem. The higher current might melt your high power drain resistors (make them go open circuit like a fusable link). I would check those first. Then check the PNP BJT that controls the CCS. The JFETs are probably fine as they conduct either way (like a variable resistor).
1. Look at R 155/116/117/118 they are 2R2 1206 SMT - probably about 1/4W and 310mA across 2R2 is about 210mW - so should be ok, but check.
2. The main rail smoothing caps C121/124 were reverse biased and probably damaged - lucky they did not blow up like a firecracker as that is the most dangerous thing to happen if your face is nearby. Replace those. In a pinch just remove them and amp will still work - re-install new ones later.
3. You might need to change C121 or any other electrolytic that was exposed to high levels of reverse polarity.
4. Check the V111 PNP BJT, replace if needed.
5. check the P-channel MOSFETs to see if they are fried by measuring ohm across G and D and G and S and D and S. Nothing should be less than kohms.
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Thanks for the pointers, X.
There as no heat or smoke, the only indication I got of a fault condition was a pulsing voltage - presumably the bench supply or perhaps the voltage regulators detecting a short.
Your point 2 is why I always wear eye protection when energising a circuit outside of a closed chassis.
Thanks again, I'll get some spares on hand and get the chassis finished in the meantime.
Just a quick update.
Replaced all elec caps on the amp board as well as both PNP v111 and v131.
Run a split rail from my bench supply and the board is trying to pull big current - not short though as PSU didn't limit.
New PNP are both 5 ohm S-D.
Looks like further digging required when time allows.
Replaced all elec caps on the amp board as well as both PNP v111 and v131.
Run a split rail from my bench supply and the board is trying to pull big current - not short though as PSU didn't limit.
New PNP are both 5 ohm S-D.
Looks like further digging required when time allows.
Ok, I shouldn't post late at night. The PNP are obviously BJT not MOS. And maybe there is a short as the current limiter was actually restricting the output.
For some reason I didn't even test the PMOS like you originally suggested
So they are all FQP3P20 and all readings are >20Meg. I can see the resistance rise with negative lead on the source and positive on the drain (charging up the fet?).
For some reason I didn't even test the PMOS like you originally suggested
So they are all FQP3P20 and all readings are >20Meg. I can see the resistance rise with negative lead on the source and positive on the drain (charging up the fet?).
If you look carefully at the photo on post 1 you can see which pins go to which pins. Follow the yellow wire - that’s +ve 18v.
The schematic will also give you the correct pin and reference pin 1.
Finally, you can look at which pins go to the +ve leg of the electrolytic capacitor.
The schematic will also give you the correct pin and reference pin 1.
Finally, you can look at which pins go to the +ve leg of the electrolytic capacitor.
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So I've replaced the PNP BJTs again and connected the power supply up (the correct way) and the board seems to be behaving properly now. I've yet to put any signal in and out but just powered up, it has very little DC offset but this does go to about 1.2v on shutdown (presumably the load will take care of that). The Mosfets are lightly warm.
I've attached a picture of the wrong way to connect the amp - 1:1 should be 1:3, 3:1
I've attached a picture of the wrong way to connect the amp - 1:1 should be 1:3, 3:1
