Sounds like you have current flowing somewhere it's not supposed to be. Don't remove the lamp, it's doing what it's supposed to and stopping a meltdown. Were you seeing any voltage across the emitter resistors (TP1 - TP2)?
I checked the R30 pot setting, and it was at the midpoint instead of full on. I corrected that.
Still get fluctuating DBT but R30 reading is -0.56 to -01.44
Still get fluctuating DBT but R30 reading is -0.56 to -01.44
When you say R30 reading is -0.56 to -01.44, where are you measuring this and is this volt or millivolts?
Current is flowing somewhere. Did you check to see if any of your drivers or output devices are shorted to the heatsink? Do you have insulators under the screws on Q14 & Q15?
No. If you'd followed the advice to install low-wattage 10 Ω resistors, these immediately would go up in smoke and open if anything were wrong and draw excessive current, hence protect the devices also.
Best regards!
I would think a resisitor, of any wattage, would have a much longer "blowing" time than a fuse. But hey, I'm not an expert. I'll stick with only fast blow fuses on my rails. Of course, even a fast blow fuse may not protect the outputs depending on the circuit, the device and the circumstance creating the short.
I ordered the pcb at Honey Badger, they shipped today. I read in the thread that some of you had problems here, but in most cases on non-original boards. I've built a few amps already, hopefully I'll be happy with the HB 🙂
Well, I went ahead and tried the 10R resistors. Got the same result: very little power across TP 1 & 2. Pulsating on/off bulb. I wonder if it's my trusty soft start. Is that getting in the way somehow? Or I have a short, but where? Any likely places to start probing? I feel confident that the pots are set correctly to begin biasing. The board looks clean, nothing burned that I could see.
That 250 to 450mA flowing with the bulb and 10 ohm resistors limiting the current. You have some problems on the amp board. Your soft-start is doing it's job but you have something drawing too much current so it resets and starts again.
Start by verifying you have the correct components everywhere. It's really easy to mix up transistor locations. Take some resistance readings between the power rails to ground. Also from the power rails to the output rail. They should all be very high resistance. Check for obvious mistakes like connecting power backwards, this is an easy mistake to do too.
Start by verifying you have the correct components everywhere. It's really easy to mix up transistor locations. Take some resistance readings between the power rails to ground. Also from the power rails to the output rail. They should all be very high resistance. Check for obvious mistakes like connecting power backwards, this is an easy mistake to do too.
You had me at "Check for obvious mistakes like connecting power backwards, this is an easy mistake to do too."
Amazing what can be accomplished when reading words correctly. 😡
The current readings with 10R resistors in are:
R7: 0.171 DCV
R30: 0.000 mV
R17: 0.006 mV
I had checked all the power rails to output rails and got high resistance.
Hopefully I will get time tomorrow to start biasing.
Xmas came early for me.
Thanks for your help.
Amazing what can be accomplished when reading words correctly. 😡
The current readings with 10R resistors in are:
R7: 0.171 DCV
R30: 0.000 mV
R17: 0.006 mV
I had checked all the power rails to output rails and got high resistance.
Hopefully I will get time tomorrow to start biasing.
Xmas came early for me.
Thanks for your help.
When biasing a First Watt, there are two pots to work with, one for bias, the other for offset. The HB has three. R30 for bias, R17 for offset. I'm not sure how to think about R7. Is the goal to keep it under 0.5V, with R30 at 44mV and R17 at 0?
Chiptech,
https://www.diyaudio.com/media/build-guides/diyaudio-diyab-build-guide-v1.0.pdf
Pages 28-30.
Best,
Anand.
https://www.diyaudio.com/media/build-guides/diyaudio-diyab-build-guide-v1.0.pdf
Pages 28-30.
Best,
Anand.