You are supposed to use the self tapping sheet metal screws in those holes. They are not tapped.
I believe HiFi 2000's switchover to PEM nuts to secure the covers was very recent. Older cases have used self-tapping screws.
I've replaced the wrong trim pots and now getting sensible matching measurements on R7 / R8 against DC offset on the speakers outs, except R7 reads negative mV to R8 positive mV.
This is with both +ve DMM clips to the "top" of the F5 PCB. I can't read the schematic well enough to know whether that's right or I have soldered something in upside-down again? 😕
I am not getting any warmth in my heatsinks either so starting to think there's something amiss.
This is with both +ve DMM clips to the "top" of the F5 PCB. I can't read the schematic well enough to know whether that's right or I have soldered something in upside-down again? 😕
I am not getting any warmth in my heatsinks either so starting to think there's something amiss.
It takes a lot of turns before you see bias voltage. Yes it's a push-pull amp so half is positive and half negative.
If you have a temperature gun check the mosfet and heatsink temp, should be close to the same.
Looking good!
Standard reminder: Don't push it to final bias value in one go. Go part way,
trim DC offset and leave the lid on unless you're making adjustments and allow
things to stabilize. And then repeat.
You should have it biased up soon.
Standard reminder: Don't push it to final bias value in one go. Go part way,
trim DC offset and leave the lid on unless you're making adjustments and allow
things to stabilize. And then repeat.
You should have it biased up soon.
Returned to the test bench this evening. DMMs still hooked up as they were last night, turned them on, powered up, all LEDs on OK - but bulb tester shining bright 🙁 In the moment before I hit the off switch the DMMs were showing me the same figures as I left it with yesterday too.
No smoke / pops, nothing visibly obvious amiss.
Going round the connections all looks fine. The only way to make the bulb dim correctly is powering up with either PSU rail disconnected from the rectifier - so maybe that points to a short somewhere on the PSU itself.
I'll try disconnecting the amp boards and see where that leads me.
No smoke / pops, nothing visibly obvious amiss.
Going round the connections all looks fine. The only way to make the bulb dim correctly is powering up with either PSU rail disconnected from the rectifier - so maybe that points to a short somewhere on the PSU itself.
I'll try disconnecting the amp boards and see where that leads me.
Before disconnecting your amp boards, a few questions:
Did you bias the amp up to the point you are now (400mV, I believe) with or without the dim bulb tester in place?
What is the wattage on the bulb you are using?
Did you bias the amp up to the point you are now (400mV, I believe) with or without the dim bulb tester in place?
What is the wattage on the bulb you are using?
Hi Toolkit,
To followup on ItsAllInMyHead's post, you cannot bias with a dim bulb tester in place.
If that's what you had done, you need to dial the pots P1 and P2 back to zero (so
R5 and R6 measure close to zero with power down). Check again that dim bulb
test passes. Then remove dim bulb and then start the bias procedure again.
To followup on ItsAllInMyHead's post, you cannot bias with a dim bulb tester in place.
If that's what you had done, you need to dial the pots P1 and P2 back to zero (so
R5 and R6 measure close to zero with power down). Check again that dim bulb
test passes. Then remove dim bulb and then start the bias procedure again.
Agh - makes sense now I think about it. I just had it sitting there under the bench...
Will return to square one tomorrow.
Will return to square one tomorrow.
Better to have discovered it now before potentially biasing to 0V7 with the dim bulb in place. Once removed, there would have been a high chance of smoke. It also helps explain why the heatsinks were so cool.
The great news is that there's a very high chance you have it all proper. 😀
The great news is that there's a very high chance you have it all proper. 😀
The dim bulb strikes again.
I've done a few rounds with it.
But survived. You will too.