Feeler: an "Eee-Zzz" christmas present...ez1073 and ez1073-500

[Harpo]

..and sometimes when I am measuring the current across it...

when you measure current across it, you shorten out this resistor and maybe paralleled parts (and maybe blow up parts connected to it that rely on the presence of this not shorted resistor).
Measuring current is in series to this resistor, or calculate the current (I=U/R) by measuring the voltage drop across this resistor with known resistance.

 

[ding]

Sorry, my bad grammar. I was measuring voltage across the resistor not current.  You are correct.

 

[Gustav]

Just finished building two of these.

Functionality seems fine on both. Mic gain works, eq works etc.

Channel one - I can measure continuity between the AGND and CGND points on the PCB.

Channel two - I cannot measure continuity between the AGND and CGND points on the PCB

I cannot identify a single difference between the two channels. Mounted in cases from Dan using kits from Colin. I feel Ive poked my meter at everything in there, but I can't figure out whats up.

Any help?

Gustav

 

[Slenderchap]

I am getting 28.5mv across the 1 ohm (R26) resistor and it wont change no matter how much I turn the bias trim resistor.

That would suggest that the output section was not working at all.... has R23 become open circuit....

... maybe R23 burnt out because of a short between the screw/shakeproof of the 2N3055 body and the ground plane ?... the pad is only just large enough for the washer.

Colin
www.audiomaintenance.com

 

[ding]

I am getting 28.5mv across the 1 ohm (R26) resistor and it wont change no matter how much I turn the bias trim resistor.

That would suggest that the output section was not working at all.... has R23 become open circuit....

... maybe R23 burnt out because of a short between the screw/shakeproof of the 2N3055 body and the ground plane ?... the pad is only just large enough for the washer.

Colin
www.audiomaintenance.com

Thanks Colin. I will check on that. What should the voltage read across R23?

 

[Gustav]

Just finished building two of these.

Functionality seems fine on both. Mic gain works, eq works etc.

Channel one - I can measure continuity between the AGND and CGND points on the PCB.

Channel two - I cannot measure continuity between the AGND and CGND points on the PCB

I cannot identify a single difference between the two channels. Mounted in cases from Dan using kits from Colin. I feel Ive poked my meter at everything in there, but I can't figure out whats up.

Any help?

Gustav

I thought I had checked the connections on R1, but apparently, not good enough.

All good

Gustav

 

[ding]

I am getting 28.5mv across the 1 ohm (R26) resistor and it wont change no matter how much I turn the bias trim resistor.

That would suggest that the output section was not working at all.... has R23 become open circuit....

... maybe R23 burnt out because of a short between the screw/shakeproof of the 2N3055 body and the ground plane ?... the pad is only just large enough for the washer.

Colin
www.audiomaintenance.com

Thanks Colin. I will check on that. What should the voltage read across R23?

Testing it further I think you are right that the output section is not working. If I crank up my audio interface preamp to the max I get sound but the hum/hiss is obviously insane. I removed the washers and tested R23 and it tests fine, 12.8 ohm. I also tested C2 and C3 (ohm test) and they seem fine also. Anyone know any voltages I should be checking in the output section? I don't want to have to replace all the components. Thanks.

 

[haystack]

I had this sort of thing with a diy project.
I had hissing, crackles and terrible noise etc.
I settled down with a magnifying glass and examined EVERY joint and realised that
even with care - I thought!- I had left a tiny gap in a soldered joint in a couple of places.

I re- soldered problem looking joints and touched up any that seemed remotely dodgey . It's all good now.
I am not saying that it's the same with your situation, but it was worth it to  start again and check all of my work in detail even though I was convinced my soldering was all fine.
hope you get it sorted
Hay

 

[ding]

Thanks Hay. I usually do this before I run power thru any of my projects. No reason not to go thru it one more time. 

 

[ding]

I have checked r20, r23, c2, c3 and c12 plus replaced the r20 and the 2N3055. I have also made sure that the washers that could have been touching ground are removed for now. I am still getting 28.5mV across r26. No change when I turn r20. I can't even measure any voltage across r7 but c12 seems to measure fine both with my capacitance metering and an ohm test. I can't test c2 and c3 with capacitance metering cause my meter will not go up that high but the ohm test checks out. 48v and 24v power checks out. I imagine the output transformer has no part in whats happening but I could be wrong. Will keep poking around and see what is going on. Any ideas welcomed. Thanks everyone. 

 

[ding]

I discovered that R6 is gounded on both sides. That means part of the 2N3055, R20 and the - of c12 are somehow making continuity with Aground. I am not sure how. I have checked all my solder points. Mmmmm. Wonder where that gound point is? 

Edit: never mind. 47ohm is too small of a resistance to use the continuity function of my meter. Tested R6 and also tested continuity with the ohm function and it checks out. Still on the hunt.

 

[Slenderchap]

I imagine the output transformer has no part in whats happening but I could be wrong.

If the output transformer were open circuit it would not work.... DC current flows through it all the time.....

Measure the dc voltages at all points in the output circuit... it may lead you to the fault.

Colin
www.audiomaintenance.com

 

[ding]

It took me a while but I checked all solders with glass again, resoldered any questionable points, followed the voltage down the path and found the bad component that was causing all the trouble. Q4! Replace that little bad boy and was able to bias with no problem. This thing sounds fantastic!!!!!!! Thanks everyone for all your suggestions. I am one happy camper! ;D

 

[Slenderchap]

This thing sounds fantastic!!!!!!!....... I am one happy camper! ;D

Excellent news.

Colin
www.audiomaintenance.com

 

[ding]

One thing with my build is that the switch for fantom power is upside down. Meaning I switch down to turn phantom on. I know one day i'm going to send 48v down the wrong mic. Ribbons I'm looking at you. I was thinking an easy dirty fix would be to cut the last posts off the switch and wire a jumper from the last pad to the front post. Would there be a better way of doing this? Another option would be to wire up a led but that seems a little more complex.

 

[ding]

Here we go again.  I made the stupid mistake of not inspecting my work before I put it together and it seems as though I left an old transistor in there rolling around. I imagine it eventually made contact with something as I jostled the unit around. Now the preamp smells like something is heating up, it makes static noises but no sound from a mic.  :'( I am getting 320mv at R26. By the time voltage gets to thru R19 it is 0v. R14 is at 2.7v. R6 is getting about 13.75v, gets very hot and smells. R9 about 1.83v. Nothing looks burned but it sure starts to smell like hot plastic from R6 if I leave it on for a little bit. Anyone have any ideas that pop to mind? Thanks.

 

[ding]

One more clue, the staticky noise is not constant. It comes up and down. Strange.

 

[ding]

Q4 had gone bad again. I replaced it but now I get 0v at R6. R7 is getting 23v on one side and 1.1v on the other. 0v at R8, R9, R14 etc. Basically something is not letting voltage thru the output stage.  ??? It seem like voltage flows from R26(23.8v) thru R23(23.8v) thru R7(23.8v) to R6(0v). C12 is fine. wonder what it could be?

 

[ruairioflaherty]

Do you know that your output transformer is good?  The DC flows in the primary.

 

[ding]

I imagine it is since it was working properly before.