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Old 17th August 2009, 01:42 PM   #11
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Quote:
with grounds lifted from ground bus, and boards attached to sink, does it still short between tab and heatsink.
I will check this tonight. Also, I have better sink pads in storage. The current pads are flimsy at best. I have the...what are they called...oxide ones in storage. They are thick.

What I don't understand is how the hex bolt could make contact with the case. There is a gap of plastic seperating the metal part on the back of the FETs. I do have shoulders

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If you are using the Zetex transistors, make sure that you have the P and N devices correctly oriented (not as shown on the silkscreen).
I'll triple check the Zetex trans. From memory, I can say the Zetex cbe are reversed from the BC trans.

I believe I have 2 seperate issues, maybe multiple ones for each channel. Can't rule that out.

Guessing since voltages are ok (not great) and the fuse isn't blowing, that I'm partically there? Could be worse, right?

Here's a pic of testing. Using 2 digital and one analog. all the test equipment I have, although I can grab a o'scope from storage, but not sure how to use it.
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File Type: jpg f5testing1.jpg (94.5 KB, 364 views)
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Old 17th August 2009, 02:04 PM   #12
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Thanks for the input Babowana, and to everyone for giving their valuable time to help.

Thanks,

Vince
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Old 17th August 2009, 02:53 PM   #13
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Another thing I should have mentioned was that, against good advise, I did hookup speakers to the amp. there was absolutely no sound at all. No pops, hum, hiss or distortion.

Maybe because I burned out the voice coils!
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Old 17th August 2009, 06:37 PM   #14
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Originally posted by vdi_nenna


I'll triple check the Zetex trans. From memory, I can say the Zetex cbe are reversed from the BC trans.

I believe I have 2 seperate issues, maybe multiple ones for each channel. Can't rule that out.

Guessing since voltages are ok (not great) and the fuse isn't blowing, that I'm partically there? Could be worse, right?

Here's a pic of testing. Using 2 digital and one analog. all the test equipment I have, although I can grab a o'scope from storage, but not sure how to use it.
Yeah, you're right the zetex should be placed with the curved side reversed from the footprint on the boards. You can also pull them out when you get desperate - they are not essential for adjusting the bias.

Have you tried comparing the working channel to the bad one - any differences? What about the jfets - have they been swapped n/p channel?

Regarding the adjustments, the purpose is not only to get the current through R12 and R11 to be approx 1.3A (0.59V/0.47ohm), but also to adjust the DC output. You could try to turn down P2 (low resistance) until you get ~0V on the output and then check what your voltages are over R11 and R12.
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Old 17th August 2009, 07:30 PM   #15
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Have you tried comparing the working channel to the bad one
I think I have 2 bad channels. Different issues in each.
The one channel I'm sure is shorted somewhere, possiblly the FETs or the input. I remember the input of 1 RCA being real tough to insert the male RCA. It popped and then it went in, so I have to investigate.

The other channel, I get -8.5v at the output.

Both channels warm up gradually as if they were working fine.

Do you know if connecting the F5 PCBs GND OUTs to the output jack require additional grounding to star or power ground?

I have the PS boards grounded to a single point, then to earth ground. The audio PCB has a GND out and it goes to the speaker jack on the chassis only. Should it also go to star or earth ground?

Thanks,

Vince
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Old 17th August 2009, 07:48 PM   #16
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Quote:
Originally posted by vdi_nenna


I think I have 2 bad channels. Different issues in each.
The one channel I'm sure is shorted somewhere, possiblly the FETs or the input. I remember the input of 1 RCA being real tough to insert the male RCA. It popped and then it went in, so I have to investigate.

The other channel, I get -8.5v at the output.

Both channels warm up gradually as if they were working fine.

Do you know if connecting the F5 PCBs GND OUTs to the output jack require additional grounding to star or power ground?

I have the PS boards grounded to a single point, then to earth ground. The audio PCB has a GND out and it goes to the speaker jack on the chassis only. Should it also go to star or earth ground?

Thanks,

Vince
You must have a gnd connection between the boards and the psu, input and output. The topology (what kind of start) you choose will affect only the noise level.

You could try to edit my picture:
http://viller.eu/audio/2009jan_gbf5/...74_wiring1.jpg

and show your wiring scheme.
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Old 17th August 2009, 07:53 PM   #17
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I had the picture with me yesterday when doing the wiring.
It speaks for itself- straight forward.

I added a GND connection from the end of the PS board to a star point. That's the only difference.
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Old 17th August 2009, 08:19 PM   #18
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Another thing I remeber is the jfets were very warm to the touch.
not impossible to touch, but very hot. Is this normal?
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Old 17th August 2009, 08:29 PM   #19
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I don't remember them being very hot. Sounds like time to start debugging...
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Old 17th August 2009, 10:34 PM   #20
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Tea-bag and All,

With the left channel boards attached with the ground bus intact, there's continuity...it's shorts. Lifting the ground form the bus there is no continuity...no short.

I also found that the input on the left or right are not shorted, but the positive speaker out on the left is shorted!! This is with the board off the heat sink and ground attached.

I found the aluminum oxide pads. I'll clean up the goop and feel around for burs in the heatsinks.

Can I assume the FETs are burned at this point?

Thanks,

Vince
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