Salas hotrodded blue DCB1 build

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Hi; I've got a couple of quick questions regarding the blue edition pcb board.

The .22u/100uf caps in the middle - what up with that? Is it two caps ( 1x .22uf and 1x 100uf) or something else?

I've noticed two resistors just before v+ / v- out (labelled '1') - are these on the BOM?

Thanks,
JG

1 Ohm resistors indeed. Test points use for those setting various voltages when used as a PSU unit for other stuff. You can either install or jumper them in a full DCB1.

Its 2 places (one per channel) for 0.22uF or even larger value plastic caps with many holes to aid size variation. The 100uF option is again for setting general PSU. Ignore the 100uF in a standard full DCB1 blue use. Films play better for it there.
 
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Is it safe to test the regulator section unloaded (no parts installed in the buffer section) ?

Isn't the 10R current setting resistor quite over-spec'd at 5W (chance of burning it out zero under absolute worst case) ?

Theoretically yes, it seems too much, but after builders found the 2W ones hot enough (what it burns it burns it all the time, no pause, the body accumulates heat), they concluded a 5W part worked most comfortably.

No danger to test this one without a load.
 
Hi Salas,

I am confused about something, and it's probably basic electronics. The DCB1 power supply caps are connected with + and - sides connected together, to make + and - sides to the shunt reg (hence DC coupled, I guess). What I am confused about is why in this instance the + side of the bridge can feed the - side of the cap without making it explode. Is this the only instance in which a polarised cap can be put backwards, ie directly after a bridge?

Thanks as ever.
 
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Hi Salas,

I am confused about something,

When you have symmetric polarities around earth, then the minus supply capacitors see earth as positive relative to minus output, hence their (+) leg goes to earth where it meets the (-) leg of the positive side's capacitors which see earth as a more negative point than the positive output.
 

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I finally completed installing all the components in the regulator section, and fired it up. All the LED's lit up. Output voltage measured at +10.58/-10.56. Waited a few minutes...... then I notice a bit of smoke rising!

I shut it down immediately and tried to spot which component was smoking, but no visible evidence. I also noticed that the heatsinks on the postive rail MOSFETS were substantially warmer than those on the negative rail.

I then proceeded to power it back up for a few seconds at a time, and take some quick voltage measurements. What I found was that the total voltage across the three current setting LEDs on the positive rail was 7.6v, and should be slightly under 6v. This would explain why the MOSFETS are running hotter, probably closer to 400ma than 200ma (using 10R current setting resistor).

So it appears that the current being drawn from these LEDs is much too high. Could it be that I have a bad JFET between the LEDS and the 100R resistor that is causing the extra current draw?

Now I'm blowing fuses, so I'm having a much more difficult time troubleshooting. Any ideas would be welcomed.
 
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First thing I would look for is the K170 CCS JFET that sits on the 100R. Measuring across the 100R, translating into current. Between 6-10mA from a healthy BL. The smoke must have let go from the respective 10R current setting resistor if has 4V across. Then again, a bad CCS Mosfet could not be giving enough Vgs. The one associated with the 10R. Maybe punched through with static when handling.

If blowing fuses, just use DCmA mode on DVM, put it in series with a 9V battery, and feed the K170 as it is on board with power off, pin 1 (+), pin 3 (-). If it will be a short, its the culprit. If it will show normal IDSS, then look for changing the CCS Mosfet, if the leds are beyond doubt. Have you seen them showing weird color?
 
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Choosing those you will need to solder either just one 0.1uF, or one above and one underneath, since they don't come in 0.22uF as far as I remember correctly. Bit strange but entirely doable. In such a case, yes you will need 4 0.1u in total. They are 5mm, the 100uF marked position will suit.
 
First thing I would look for is the K170 CCS JFET that sits on the 100R. Measuring across the 100R, translating into current. Between 6-10mA from a healthy BL. The smoke must have let go from the respective 10R current setting resistor if has 4V across. Then again, a bad CCS Mosfet could not be giving enough Vgs. The one associated with the 10R. Maybe punched through with static when handling.

If blowing fuses, just use DCmA mode on DVM, put it in series with a 9V battery, and feed the K170 as it is on board with power off, pin 1 (+), pin 3 (-). If it will be a short, its the culprit. If it will show normal IDSS, then look for changing the CCS Mosfet, if the leds are beyond doubt. Have you seen them showing weird color?

Measured 7.8mA through the suspect K170 (sitting on the 100R). I guess I need to order another 9240 Mosfet along with a gross of fuses, and replace the 10R while I'm at it. Thanks Salas.