[BUILD] 1176LN Rev D DIY

[tazman]

I have a DMM, as I stated above.
As I am going through the resistors in circuit, the values are not reflective of their true value as they are in circuit.  To get an accurate reading I have to at least lift one leg.

As for the caps, I don't know of any easy to test them with a DMM in circuit, maybe I'm wrong.

 

[colombian]

Problem solved. It was NOT the OT.

Good luck with your projects.

Hello All,

First I want to Thank you for this great forum and all the contributors!!

Second, I have an issue you may help me fix. I just finished building a Hairball kit audio using the BOM and mnats rev 2.2 board. My PCB is labeled "v2.2 26.01.09".  the board shown in the "v2 building" document on mnats Rev D page is dated 30.04.08. 

Since i knew in advance about the famous R32 burning out, I checked and double checked the Output Transformer wiring were correct and belonged to rev 2  board + diagrams....  I turned on the compressor and the R32 GONE in 10 Seconds!  very strange......  since I use rev 2 and all color match the wiring guides from, MNATS it, it is pretty straight forward but yet.... R32 is burned... 

I triple-read this forum but it mainly references to incorrect OT wiring from rev 1 to rev 2.... nothing else.  which is NOT my case.

I took out white/red wire and measure +30V  DC  between that wire and the ground (violet wire)  so no wonder the 39ohm resistor burns.....  any idea?

I looks like the Hairball output transformer came damaged?  is there any way to test it?  what else could i check?

I added a few pictures to show wiring.

Thanks a lot to all of you!!!
God Bless

Ludwing

 

[dandeurloo]

Tazman can you use the color code to check values instead of lifting legs on every resistor?  Seems like that would be worth checking into.

I have a DMM, as I stated above.
As I am going through the resistors in circuit, the values are not reflective of their true value as they are in circuit.  To get an accurate reading I have to at least lift one leg.

As for the caps, I don't know of any easy to test them with a DMM in circuit, maybe I'm wrong.

 

[tazman]

Yeah, i just finished checking the colors for the 3rd time.  They all match!  I replaced the 2N5457's, no difference.

I just rechecked the wiring and it all looks correct.

I checked the caps (reading the values) and they match the schematic.

Not sure what else to check.

 

[dandeurloo]

did you reflow all of your connections in case you have a bad solder joint that you can't see?

 

[tazman]

I did a lot of them.  I have not re flowed them all.  I'll do that next.

Thanks,

Rob

 

[Stagefright13]

I'm looking at your posts Tazman. I am an amateur tho remember.

John

 

[Stagefright13]

Short of destroying the lands unsoldering all those components..... You most likely Have wired it incorrectly. Do you have any pics to show? They help us A lot. The board is very simple to solder etc. Great design and high quality.

Take some high res pics. So we can see.

John

 

[tazman]

Here are a few pics.  The wiring is not as neat as it should be cause I undid a lot of the zip ties while trouble shooting it:

 

[tazman]

Ok, I put the pictures here:

http://www.robertocerini.com/1176/

Thanks

Rob

 

[Majestic12]

The cap next to R25 doesn't seem to be in good condition, looks like there is rust or something on the top.

 

[tazman]

Hi Majestic 12 -  I think you're seeing the gold label and its reflection from the side to the top.  I looked at the cap and it seems fine.  I'll check it again, just in case.

Thanks

Rob


Edit:  I checked them last night and they look fine (visually).  Unfortunately it was just a bad reflection from the camera (I so wished it was a bad cap, that would have been easy to fix!).

 

[tazman]

Hi John - did the pictures help any?  Should I take some more?  I'm really open to any suggestion at this point.  I'm stuck as I don't know what else to look at.

Thanks,

Rob

Short of destroying the lands unsoldering all those components..... You most likely Have wired it incorrectly. Do you have any pics to show? They help us A lot. The board is very simple to solder etc. Great design and high quality.

Take some high res pics. So we can see.

John

 

[tazman]

Could someone post their voltage readings at Q3, Q4 and Q8?

One of the members here sent me his readings and mine at those locations are way off.  BUT mine match the Gyraf readings at those locations!?!?  I'm a bit confused about the coincidence!

Thanks,

Roberto

 

[tazman]

I just checked the input trafo and found that the output + and - are shorted to each other!!! 

Edit:  never mind.  There is small resistance of 13 ohms which is normal for this trafo.

 

[tazman]

Solved.  Bad cap and bad output pot.

 

[Majestic12]

Which cap was it ?

 

[baadc0de]

Solved.  Bad cap and bad output pot.

Congratulations! I had my fingers crossed you'll find the error

 

[tazman]

I didn't find it, Mr. Kulka did   I got to the point where I was stuck.  I brought it to him and he was able to identify the issue.  He mentioned that it was not obvious.  The cap is part of the distortion canceling part of the circuit.  All the values were correct, just the cap was bad.  He also found that the output pot was not tracking correctly.

Great guy.  Money well spent.  Now I know I have a unit that works as it should.

A good lesson learned for the next one

Rob

 

[Majestic12]

Thats good, congratulations

When I made the measurements on the transistors I plugged in a headphone directly at the output of my unit and realized that there was a big amount of hiss that when I turn up the output pot.

Same with your unit ? I'm just wondering, I haven't used mine in a recording session yet.