| neil_kaye |
Hi its me again...
The story thus far. One channel works great, which emboldened me to build the second.
The second one not so good. The history of the not so good channel is this:
1. With the chassis open, and everything in place I tested it on an old pair of speakers and a beautiful melodious sound eminated.
2. Put the two halves of the chassis together and a serious hum appeared.
3. After much poking and disassembling i discovered that the JFET was grounding through a washer (damn those fets are small) onto the chassis. When the two halves were not joined the voltage didn't go anywhere, upen closing the voltage was draining out through the speaker terminal, by way of the star ground... I think
4. Great i thought, just to make sure i pulled the FET off and with it hanging in space i tried the amp again, and it all seemed fine, reatatched the FET and all looked good.
5..... or so it seemed. After an hour "POP" and no sound.
So know i am sure something has blown. I am new to this and this is about as much as i have managed to determine.
1. At the DC i measure a potential difference of 52V which is higher then the 46V that i was getting before and the 46V on the still working channel.
2. Where i used to measure the voltage at R18 and R7 and set it at 23V (half of 46V) I get almost nothing, 2 or 3 volts.
3. At the speaker terminals there appears to be a very minor extremely unstable something in the millivolts and a minor pop st the speaker on power off.
I have order more JFET's because i assume the JFET has gone and possible the MOSFET's.
How can i trouble shoot this, maybe a resitor went or something else? No burn marks on board so no serious short.
Ant and all help would be greatly appreciated
Thanks |
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| neil_kaye |
| Help anyone please :scratch: |
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| trango |
Hi,
I'm sorry to hear that you are having trouble with your Zv9.
Did you attach the JFET to the heatsink properly when you did the second test? Since you had it up an running for an hour, it sounds like some temperature related issue :confused: ?
/Trango |
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| neil_kaye |
Thanks Trango.
Would fault would a tempertature reltated issue likelt cause. I am trying to figure out what would have blown. I imagine one of the FETS? |
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| neil_kaye |
| On a related issues. How have you managed to attach the JFET to teh heatsinks as there are no mounting holes??? |
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| thomaseliot |
| quote: | Originally posted by neil_kaye
On a related issues. How have you managed to attach the JFET to teh heatsinks as there are no mounting holes??? |
Hi Neil
http://www.diyaudio.com/forums/attachment.php?s=&postid=888994&stamp=1144527606
this is how Steen managed it.
Please, post some pictures of the opened chassis (both parts) so somebody can realize better what's going on when you close it.
Are you sure all mosfets are well insulated? (Measured mosfet tabs and chassis ground for shorts?) |
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| trango |
I'm using clips bought from Mouser in combination with AluOX insulators and thermal grease.
They are not avaible in the right format for the JFET but I used the smallest size they sell at mouser and it seems to be working. I've acutally tested my Zv9 for the first time today, everything seems to work - only final assembly left.
The picture below may give you the idea even though the JFET is not visible... |
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| thomaseliot |
trango,
the picture is too small. Have you a part number for Mouser insulators?
Congratulations for another Zen playing :D |
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| neil_kaye |
| thomaseliot, the mosfet may indeed be a problem as well as a heatsink issue (i think it is a combination of both). How do i measure mosfet tabs and chassis grounds for shorts? |
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| thomaseliot |
| quote: | Originally posted by neil_kaye
How do i measure mosfet tabs and chassis grounds for shorts? |
With Ohm meter. One probe to heatsink (in a screw hole) the other to tab.
If resistance is zero, then there is a short (probes are connected), otherwise resistance is infinite, that is, there is no connection between probes. |
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| trango |
| quote: | | The picture is too small. Have you a part number for Mouser insulators? |
Yes, now I see that the picture is to small. Try the part numbers instead!
Clips; 532-MAXCLIP07G
AluOx pads; 532-4170
| quote: | | Congratulations for another Zen playing |
Thank's It has been so fun to build it! I have parts and PCBs for two more channels of Zv9 and I think I will build a second one soon... |
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| ZUM911 |
Hi,
I'm casing up my ZV9 based on Veteran/Peter Daniel's boards. When everything is wired up with star ground to mains earth through thermistors the fuse blows while powering up through a variac. I've removed the lead from the star ground to mains earth and power up with no problem but I measure the full rail voltage potential between the star ground and mains earth. Every thing seems right and the fets are insulated with mica and silicone paste. I've studied many examples of the star grounding scheme posted here and I can find nothing obviously wrong. Thanks for any guidance.
Rick |
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| Hartono |
Hi Rick,
did you insulate the FET bolt ?
Hartono |
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| ZUM911 |
Hi,
Thanks for the replies. I'm using the exact wiring scheme shown in post 24 and the fets are all insulated and verified that they are not shorted. I've double checked everything I can think of and the amp is playing music so in that regard it's working.
Rick |
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| sts9fan |
I am posting to this thread to see if anyone can help me with my Zv9. I got it all together and only one channel is working. The one that is not working is still getting warm and there is a slight hum from the speaker. The output is reading ~0.02v constant. I trimmed Q2 to be half of Q3 ~22v. Both PS are putting out 49v. There was/is no burning smell or smoke.
Also I have attached the signal gnd to the chassis via a thermistor as has been discussed in other threads. With this attached I was getting different resistance readings from all over the board to chassis. I was not sure if this was good or correct. I removed the attachment and that was the point.
Any help would be fantastic but go easy I am new.
Kris |
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| Magura |
First thing to check is if you have shorted something when you soldered.
Even a thin, thin whisker can cause this sort of issue.
Magura :) |
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| sts9fan |
I think I have checked the board for any shorts and found nothing. Anyone have a wiki on troubleshooting an amp like this? I think I may just measure the voltages all over the board and look for differences. Is that the way to do it?
In what order do you usually check stuff to narrow down the issue? I am getting nothing on the input and very little on the output. I suspect it is the input though because there is some hum coming through the speakers. And in my random testings when I put the probe on a small cap it caused a louder hum from the speaker. This happened both sides so I suspect its normal. |
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| Magura |
Well, have you triple checked the component values and orientation?
Magura :) |
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| sts9fan |
Thanks will do.
If you think you have an input issue where would you start looking? |
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| sts9fan |
The Jfet on the working side is reading constant 4.3vdc while the non-working is 5.0vdc. Is that significant?
???? |
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| Magura |
| quote: | Originally posted by sts9fan
Thanks will do.
If you think you have an input issue where would you start looking? |
Well, first I would make sure it is an input issue ;)
So far, there are about 99% chance that it isn't.
Magura :) |
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| Magura |
| quote: | Originally posted by sts9fan
The Jfet on the working side is reading constant 4.3vdc while the non-working is 5.0vdc. Is that significant?
???? |
You need to take a photo of the upside and the downside of the project.
This way we have a chance to see if you have done something wrong. Next you can take a schematic, and post the measured voltages.
If you want to go try fix this yourself, compare the measurements of the good and the bad channel, and see where something is significantly different.
I personally would not take much notice of 0.7V difference, between a working channel, and a bad channel.
Magura :) |
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| sts9fan |
| ok I will post a picture. Don't be too tough though because I soldered this over a year ago and had no idea that lead-free solder was so hard to work with. Live and learn. |
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| sts9fan |
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| Magura |
I think I'd start out by cleaning those boards. Alcohol should do. Then you can see if something is touching.
Magura :) |
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| sts9fan |
Here we go looks a bit better. I am having a hard time taking a picture. I am going to try and fix some of the solder joints carefully. Thanks for your help. Next I am going to take measurements and put them on the schematic.
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| MikeW |
| If you can't get it working in a couple of weeks, bring it up and I'll try to help. :smash: |
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| sts9fan |
| Thanks Mike. I hope to be able to get it working soon. I am going to put some hours in tommorow. |
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| Magura |
Next step would be to re-solder all the joints, with 40/60 solder. Then clean it up again, and see if it didn't begin to behave.
Magura :) |
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| sts9fan |
FIXED!!!!! Shockingly there was a blob of solder where it did not belong. Thanks for your help!
Kris |
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| Magura |
Great :D
Enjoy!
Magura :) |
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| sts9fan |
Here it is connected to my test speakers
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| MikeW |
| I am glad you got it working. What are you going to use for the front? |
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| sts9fan |
| I have a nice board of cocobolo that I am going to use make a faceplate. I figured after putting my lack of metal working skills to the test I would test my lack of woodworking skills.:) |
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| Magura |
| quote: | Originally posted by sts9fan
Shockingly there was a blob of solder where it did not belong. |
Actually this is not shocking at all ;)
I have been helping many "first projects" over the years.
When such are not working, 99% of the cases, it is due to one of these reasons:
1) Component misplaced, or turned 180 degrees.
2) A solder "blob" .
3) A solder whisker hiding in the flux residue.
4) A bad solder joint.
5) Wrong polarity of external connections
So, it's a rare newbe problem, that is not fixed by the above checklist.
Magura :) |
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| Magura |
| quote: | Originally posted by sts9fan
I have a nice board of cocobolo that I am going to use make a faceplate. I figured after putting my lack of metal working skills to the test I would test my lack of woodworking skills.:) |
Sounds like a great idea.
Magura :) |
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| sts9fan |
| I guess I forgot my sarcasm font.:cool: |
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| Magura |
| quote: | Originally posted by sts9fan
I guess I forgot my sarcasm font.:cool: |
:D
Magura :) |
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| jacco vermeulen |
| quote: | Originally posted by sts9fan
test speakers |
Are me weary eyes deceiving me, or are those tuned Scotch bottle loudspeakers ? |
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| sts9fan |
| They are actually what we call in the biotech biz "media bottles". I had those 2" Tang Band wideband drivers and thought it would be fun to throw them into a mini 1/4 wave straight pipe. they are actually fun to listen to. I listened the whole hour while the amp was warming up to re-adjust p1. |
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| jacco vermeulen |
| El Pipetto :clown: |
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| MikeW |
| How do you like it so far? |
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| sts9fan |
| I am really enjoying this amp. I am happy to have a good amp in the house. |
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| MikeW |
| Chris if you are running full range speakers you may want to increase the feedback resister. I went up as high as 1.5 Meg. I am back down to 470k. It gives you a little more bass with the full range and some more gain. Let me know if you need any extra parts, Mike.:D |
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