jsteiger

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #960 on: September 10, 2018, 10:46:30 AM »
Hey,
I've got a problem with one of my Gar2520s in a VP28. The thing started giving off a wicked smell the first time I put it in my lunchbox, and it seemed to be coming from the op-amp. I tested that same op amp in my other VP28 that has been working perfectly, and same thing happened. This time around, however, I noticed the R9 and R13  56R resistors had been totally fried black :/ And may have singed the neighboring caps.  I double checked all of my resistor placement, transistor placement, solder bridges, and I'm not coming up with any reason.

Any ideas? Thanks in advance!
Sounds like this should be posted on the gar2520 support thread.
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Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #961 on: September 11, 2018, 03:34:19 AM »
If you follow the steps in the Test Point guide, all measurements shown are done in Line mode, not Mic mode. What is your reading at TP1 when following the proper procedure?

Just wanted to follow up on this. I upgraded my multimeter to get a more accurate reading. Here are my test results:

TP1: 110mv
TP2: 194mv
TP3: 194mv
TP4: 47mv
TP5: 47mv
TP6: 47mv
TP7: 47mv
Output: 35mv

Just so you guys don't have to read through the thread: my preamp gain switch isn't affecting the signal and I'm getting an extremely low level. I have litz transformers and I also have two pre built red dot amps. I went back and checked for cold solders and reflowed anything that looked like it might be an issue. Above are the current readings of my preamp.

jsteiger

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #962 on: September 11, 2018, 09:47:26 AM »
Just wanted to follow up on this. I upgraded my multimeter to get a more accurate reading. Here are my test results:

TP1: 110mv
TP2: 194mv
TP3: 194mv
TP4: 47mv
TP5: 47mv
TP6: 47mv
TP7: 47mv
Output: 35mv

Just so you guys don't have to read through the thread: my preamp gain switch isn't affecting the signal and I'm getting an extremely low level. I have litz transformers and I also have two pre built red dot amps. I went back and checked for cold solders and reflowed anything that looked like it might be an issue. Above are the current readings of my preamp.
Its very hard to tell in the pic but R8 does not look like a 20k?? Your problem starts with TP2 which indicates A1 or the support circuitry around it. That would be R5-R8 as well as R1, C1 and then the gain-switch R's.

Just to rule things out, I would swap the red dot positions and see if anything changes. I have never received a bad opamp from Scott though so I doubt this will change anything.
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Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #963 on: September 12, 2018, 07:48:49 AM »
TP6 is post the fader booster amp so I would look at that.

I just wanted to let you know I got the issue traced and sorted.  Thanks for the help!  Funny enough it was the 6/12db switch that was somehow bridged to ground. The output of the HPF board was getting continuity to ground and not passing audio.  Once I got rid of that the VAC readings went back to normal and I get to keep my hair and sanity  :)

Thanks for the great kits and amazing support. 

Cheers,

Jeff

CaseyI

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #964 on: September 12, 2018, 03:40:23 PM »
I've just completed my VP28 and it has some issues.  The Signal LED is lit when my 500 rack is powered OFF, and it turns off when I power the rack on.  I can't do any audio tests as I've also managed to fry R14 and R15 on my Gar1731.  Any help is appreciated.

Thank you,
Casey
« Last Edit: September 12, 2018, 05:15:29 PM by CaseyI »

jsteiger

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #965 on: September 13, 2018, 12:04:59 PM »
I've just completed my VP28 and it has some issues.  The Signal LED is lit when my 500 rack is powered OFF, and it turns off when I power the rack on.  I can't do any audio tests as I've also managed to fry R14 and R15 on my Gar1731.  Any help is appreciated.

Thank you,
Casey
I honestly have no idea how this can be happening. It makes zero sense to me.
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CAPI is not affiliated with, endorsed by, or sponsored by API.

CaseyI

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #966 on: September 16, 2018, 08:38:21 PM »
So I figured out the issue with my 1731 which was I transposed the Q7 and Q8 which led to frying R14 and R15.  Now that I've got that sorted out I've discovered that I've also fried PR1 and PR3 and the board itself.  I don't have spare resistors on hand but at least I have some direction on getting this thing up and running.

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #967 on: October 06, 2018, 07:12:05 PM »
Hey Jeff, I've been tracking with the vp28 for a while now and it's been sounding great, I mean great. But last night I was tracking and halfway through the volume just cut completely almost to nothing. Fired it up this afternoon and again the same thing happened it sounded great and then completely cut out after about 10to 15 minutes. Any ideas?
Thanks

dmp

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #968 on: October 08, 2018, 10:23:55 AM »
Hey Jeff, I've been tracking with the vp28 for a while now and it's been sounding great, I mean great. But last night I was tracking and halfway through the volume just cut completely almost to nothing. Fired it up this afternoon and again the same thing happened it sounded great and then completely cut out after about 10to 15 minutes. Any ideas?
Thanks
Sounds like something in heating up and failing. Check that the power supply is not the problem. Thermal fuses sometimes kick off.
If it is a problem on the vp28, after it cuts out examine it for any hot components.

 

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