diyAB Amp The "Honey Badger" build thread

[Chiptech]

Did you have fuses installed and did they blow?

Fuses did not blow. Photos to follow

 

[Chiptech]

Right channel amp board photos

 

[jwilhelm]

Do R32 and R33 still measure okay?

 

[Chiptech]

They both read 22R.

 

[jwilhelm]

You're going to need to measure continuity on all the power and ground rails on the amplifier board and the supply board. Also test the LEDs, R51 and R52. Something must have catastrophically failed to interrupt current on the power rails.

 

[RickRay]

I do notice that the heatsink for the front end is fairly thick. Are you sure none of the transistor legs are shorting out to the heatsink?

 

[Chiptech]

I'm checking my right channel resistors, but I've noticed I neglected to install the 1/2w - 1w 12-15V zener diode for my cascode option [#1].

I will put it in now. Could this have been causing my issue?

Does it matter if its 1/2 w vs. 1W?

 

[jwilhelm]

1W is fine there. This could be causing the strange behavior of the amp, but it wouldn't stop the LEDs from lighting.

 

[Chiptech]

Ok. I only have a 12V 0.5W diode. Will that work?

I will finish my board exam.

 

[Chiptech]

I do notice that the heatsink for the front end is fairly thick. Are you sure none of the transistor legs are shorting out to the heatsink?

I checked them all for shorts. All good.

 

[jwilhelm]

12V is too low, the BOM calls for 15V.

 

[janusz]

Ok. I only have a 12V 0.5W diode. Will that work?

I will finish my board exam.

0.5W is Ok, should be 15V but try 27k as R19 first, attached is one of the latest versions of HB

 

[Chiptech]

My review of the resistors reveal I have questions about:
R45, R47 and R49.
I can replace them.
Should I also replace the transistors related to them: Q20 & Q16?

 

[stuartmp]

@Chiptech I had a quick look at the your photos, I would be inspecting all of those pads especially the close transistor ones for bridges. It maybe a good idea to remove some solder from those pads to prevent bridging issues and to prevent running into creepage problems.

 

[stuartmp]

I believe this is the latest schematic.

 

[Chiptech]

0.5W is Ok, should be 15V but try 27k as R19 first, attached is one of the latest versions of HB

Try R19 at 27K before adding the zener? Not quite clear on that.

 

[Chiptech]

@Chiptech I had a quick look at the your photos, I would be inspecting all of those pads especially the close transistor ones for bridges. It maybe a good idea to remove some solder from those pads to prevent bridging issues and to prevent running into creepage problems.

Thanks. I will review them closely.

Can you say more about "creepage problems"?

 

[Chiptech]

I have reviewed the latest BOM and note the following changes:

Confirming that Trim pot R30 goes from 300R to 200R?

I can update my board after a few parts come in.

 

[Chiptech]

12V is too low, the BOM calls for 15V.

I found them in my stash. Yea.

 

[stuartmp]

Can you say more about "creepage problems"?

You need a certain amount of gap between the solder pads depending on the difference in voltage otherwise the voltaged can jump the gap. There are creepage tables on online. For example if the difference in voltage between two pads is grater than 64v but less that 81v the gap between the two should be 1.3mm so if you have a massive blob of solder on those pads you will reduce the gap with could allow the voltage to jump the gap, just like a short.