Because there was bulb tester in the circuit the Mosfet might be ok… Regardless, they all need to be removed, so test them when they are out.
Incredibly useful and inexpensive tester, the Mega328 -
https://www.amazon.com/Mega328-Digital-Transistor-Resistance-Capacitance/dp/B07WT9VVZB
Incredibly useful and inexpensive tester, the Mega328 -
https://www.amazon.com/Mega328-Digital-Transistor-Resistance-Capacitance/dp/B07WT9VVZB
Thanks ItsAllinMyHead. I'll wait for others to chime in. My only electronics test equipment is a VOM. Is that sufficient to test the mosfets?
Thanks 6L6. Just ordered the checker. Would you say that the chances are 50-50 or better that the mosfets are OK?
No idea. This is literally the first instance I’ve ever seen of somebody doing this.
If they are good it’s because the dim bulb tester was installed. 🙂
If they are good it’s because the dim bulb tester was installed. 🙂
I got the mosfet checker and got the following values: 4.57, 4.50, 5.48,4.56, 5.12, 4.57, 4.88, 5.06 nf. All measured 3.5 volts. Again, noobie here. Do these seem good?
most likely yes
but: nF ( capacity) - irrelevant; what counts is that tester sez they're mosfets and there are not shorts (tester should cry)
if you succeed bending pins the other way ( try to flatten them first, then bend few mm away of previous point ) take care of thermal interface - use either Keratherm 86/82 from Store or Alumina Oxide pads+goop or mica + goop
check for shorts between heatsink and mid pin of mosfet when torqued
if not sure, post pics here and inform, prior to powering up
but: nF ( capacity) - irrelevant; what counts is that tester sez they're mosfets and there are not shorts (tester should cry)
if you succeed bending pins the other way ( try to flatten them first, then bend few mm away of previous point ) take care of thermal interface - use either Keratherm 86/82 from Store or Alumina Oxide pads+goop or mica + goop
check for shorts between heatsink and mid pin of mosfet when torqued
if not sure, post pics here and inform, prior to powering up
Thanks ZM. Already bent the the pins-- no problems. Got the heatsink thermo couples from DIY store but I have keratherm, too Sounds like Keratherm goop is the operative word here. Will send pictures when I get the MOSFETs back on.
OK. Mosfets back in. Sanded the mounting hole area with 800 grit. Keratherm then alumina oxide pad then MOSFET then washer then bolt. Didn't solder just in case you see something amiss.
hopsa!
why Keratherm then Alumina pad (even if I can't see Alumina pad - they're white and no less than 1mm thick) ?
you need just one of these - either Keratherm or Alumina pad ( in which case thermal paste/goop is necessary)
and - you must use split/spring washer!
why Keratherm then Alumina pad (even if I can't see Alumina pad - they're white and no less than 1mm thick) ?
you need just one of these - either Keratherm or Alumina pad ( in which case thermal paste/goop is necessary)
and - you must use split/spring washer!
I thought the pads from the DIYstore must have been alumina pads. Will have to get the lock washers.
OK. Everything is back together. Powered up using dim bulb tester. Tester came on dimmed then brightened. All amp LEDs all stay on brightly and evenly. Turned power off immediately and just wanted to check in with you guys when I had something to report. Does this sound like I'm on the right track. Don't want to apply power for setup unless things so far seem to be in order.
Update. Powered up without dim bulb tester. Did preliminary bias and offset setup. Everything seemed to be working fine. Came back today to finish things up (leave it on for 1/2 hour and readjust bias and offset) and not quite so OK. Readjusted one side with no issues. The other side bias adjustment seemed to be going ok except everytime I got very close to 400 mv the meter would go back to zero and then climb back to almost 400 mv and go back to zero. Adjustment to the pot doesn't seem to have an effect. The LEDs on this channel stay brightly lit after power down whereas the side that seems to be working fine starts fading fades after a minute or two and then goes out. This amp had a dual mono block power supply. Ideas? Next steps?
usual
check of all solder joints
replace small BJT in Aleph CCS
replace trimpot in Aleph CCS
Aleph CCS is mosfet at positive rail and everything surrounding it
check of all solder joints
replace small BJT in Aleph CCS
replace trimpot in Aleph CCS
Aleph CCS is mosfet at positive rail and everything surrounding it
bipolar junction transistor. In this case the NPN transistor Q4/ZTX450 in schematics as shown here: https://1.bp.blogspot.com/-OVlWDQc4...GUD8kgKsfR8UgCLcBGAsYHQ/s1650/aleph_j_sch.jpg