here are the readings taken relative to ground
1st MOSFET 27.2v, 27.2v, 21.9v
2nd MOSFET 27.2V, 0V, 27.2V
1st MOSFET 27.2v, 27.2v, 21.9v
2nd MOSFET 27.2V, 0V, 27.2V
You just had to measure difference between pins 1,3 but it can be calculated from what you got ref to ground also. The second set of measurements shows a dead Mosfet with no Vgs voltage developed. That will not exclude other semis are hit, but change that one first.
Cheers Salas and Andrew,
I suspected Vgs was that measurement, but also was interested in the other readings relative to - plus felt safer with only one dmm probe near the MOSFET pins.
Have now swapped out all of the sk170s in the regulator section and both misdeed, just in case. Have not changed the c550 as didn't have a spare. Still getting the same readings across the misdeed.
When I removed the pcb I could see that the there was a small trace of solder shorting the + rail to gnd just before the B1 section
I suspected Vgs was that measurement, but also was interested in the other readings relative to - plus felt safer with only one dmm probe near the MOSFET pins.
Have now swapped out all of the sk170s in the regulator section and both misdeed, just in case. Have not changed the c550 as didn't have a spare. Still getting the same readings across the misdeed.
When I removed the pcb I could see that the there was a small trace of solder shorting the + rail to gnd just before the B1 section
I am assembling a second Hotrodded DCB1; first stage with 10 0hm resistors and wondered if 3 amp/100V Schottky diodes would be ok instead of MUR860's? I have some in my parts bin is all.
silly question here 😀
did someone make some consideration wherever,
about resistor type in "quality resistors" positions?
don't know if buying takman metal resistors, or carbon ones
did someone make some consideration wherever,
about resistor type in "quality resistors" positions?
don't know if buying takman metal resistors, or carbon ones
Selectronique have a sale on at the moment and I wondered if there would be any detriment to using one of there R core transformers with 12V secondaries in place of my toroid with 15V secondaries. tia.
A 12Vac transformer does not give sufficient voltage drop across the CCS part of the circuit to ensure good regulation. Aim for a minimum of 6V above the regulated voltage, i.e. +-16Vdc during worst case operating conditions.
Ok,
I gave up trying to get the + half of my dcb1 working. After changing all of the solid state components in the PS section, I was still getting the same error. I have now swapped another working dcb1 into the chassis and transferred the TX2575 resistors over.
Sounds fantastic - am using 1 ohm current regulating resistors now. The case is quite hot to touch, although I can leave my hand on it without discomfort
. It's going to warm up here in the UK over the next week, so it will be interesting to see how the B1 stands up.
If there is excessive heat what components are at risk? Am I looking at blown MOSFETs or are there other considerations?
Brad
I gave up trying to get the + half of my dcb1 working. After changing all of the solid state components in the PS section, I was still getting the same error. I have now swapped another working dcb1 into the chassis and transferred the TX2575 resistors over.
Sounds fantastic - am using 1 ohm current regulating resistors now. The case is quite hot to touch, although I can leave my hand on it without discomfort
. It's going to warm up here in the UK over the next week, so it will be interesting to see how the B1 stands up.
If there is excessive heat what components are at risk? Am I looking at blown MOSFETs or are there other considerations?
Brad
Heat is the enemy. The e-caps are the least able to take it.
They are rated at some amount of hours at a certain temp. Say 1000hrs at 85c.
That doesn't mean that they will run indefinitely at 65c.
They are rated at some amount of hours at a certain temp. Say 1000hrs at 85c.
That doesn't mean that they will run indefinitely at 65c.
Didn't you find a solder short culprit the other day? Maybe you had some PCB trace killed also? Beyond Ecaps expiring faster on radiated heat, mainly the Mosfets are to die suddenly of too much heat, maybe the setting resistors too. IF its too much in the long run of course. To talk suggestions or to guess realistically we need currents through the resistors, their ratings in Watt, temperature on them and on Mosfets bodies, on ecaps. At least a picture.
If the outside of the case is "hot to touch", then how much hotter is the internal ambient temperature?
Cheers Guys,
After a nights sleep I had already decided to increase the value of the current setting resistors - using 2.7ohm 5w ceramic wire wound resistors now. All of your comments pretty much reinforce what I knew, but was choosing to ignore in my quest for the F1 version of the DCB1. Now the case just gets warm to the touch. I was surprised by how much hotter the 1ohm current setting resistors made the B1.
I may revisit this and add a fan and improve the thermal interface between the MOSFETs and the chassis by removing the anodised finish where they are attached. I bet the lightly brushed anodised finish is less thermally conductive than dead flat aluminium.
Brad
After a nights sleep I had already decided to increase the value of the current setting resistors - using 2.7ohm 5w ceramic wire wound resistors now. All of your comments pretty much reinforce what I knew, but was choosing to ignore in my quest for the F1 version of the DCB1. Now the case just gets warm to the touch. I was surprised by how much hotter the 1ohm current setting resistors made the B1.
I may revisit this and add a fan and improve the thermal interface between the MOSFETs and the chassis by removing the anodised finish where they are attached. I bet the lightly brushed anodised finish is less thermally conductive than dead flat aluminium.
Brad