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 Post subject: Fet Amp not working
PostPosted: Tue Dec 11, 2018 7:40 pm 
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Posts: 5
]Hi, I'm new to this forum and new to BYOC pedal builds. I would really appreciate any info to get this thing working properly.
I have an original FA-1 FET but decided to build this so I could get a footswitch and LED.
My problem seems to be pointing to the Hitachi chip like several of the other forum users.
Symtoms:
LED not working.
Volume scratchy and noisy.
Bass & treble not working.
Note: clean signal through bypass switch when effect switched off.

What I tried:
1 replaced led. Still doesn't come on.
2Checked and re-checked resister color codes and placement.
3 Checked and reflowed any questionable connections.
4 Switched the Hitachi Op Amp locations. This caused the volume to stop working and the tone controls to pick up a local radio signal.

Any ideas? Thank you!


Attachments:
image2.jpeg
image2.jpeg [ 131.55 KiB | Viewed 6296 times ]
File comment: Note one IC has a small piece of masking tape on it to mark it. Thats the suspected bad one.
image1.jpeg
image1.jpeg [ 91.68 KiB | Viewed 6296 times ]
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 Post subject: Re: Fet Amp not working
PostPosted: Tue Dec 11, 2018 8:33 pm 
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Can you show us the solder side of the board, please?

And is one of the ICs twisted, or is that some trick of the light?

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 Post subject: Re: Fet Amp not working
PostPosted: Wed Dec 12, 2018 9:18 am 
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sjaustin wrote:
Can you show us the solder side of the board, please?

And is one of the ICs twisted, or is that some trick of the light?


I was looking at that too, but I just noticed the IMG note about there being tape on the IC, I think that is what we're seeing.

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 Post subject: Re: Fet Amp not working
PostPosted: Wed Dec 12, 2018 10:09 am 
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From the looks of it IC1 is installed backwards. See the photos on pages 6&8 of the build instructions.

http://byocelectronics.com/fetinstructions.pdf

Image

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 Post subject: Re: Fet Amp not working
PostPosted: Wed Dec 12, 2018 2:18 pm 
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Joined: Tue Dec 11, 2018 7:00 pm
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Thanks guys for your quick reply!
IC is not twisted. it is marked with tape for testing purposes.
Yes, and good eye, IC was in backwards but not during testing. That was an end of the night thing :D
Heres the solder side image and results of switching IC positions.

I retested with these results-

Red marked IC in IC1
Volume increases clockwise with loud crackling noise that fades in and out in volume slightly. Loudness seems equal to bypass volume. Radio interference.
Tone controls do nothing.

Red marked IC in IC2
Volume functions in opposite counter clockwise direction with diminished overall volume compared to bypass mode.
Tone controls function normally as intended.

LED does not work.
Note: loose wire in top left of IC1 photo is on the table/background and not on PCB

Thank you for your help, I appreciate it greatly!


Attachments:
File comment: IC2
image3.jpeg
image3.jpeg [ 109.77 KiB | Viewed 6252 times ]
File comment: IC1
image2-1.jpeg
image2-1.jpeg [ 108.98 KiB | Viewed 6252 times ]
File comment: SOLDER SIDE
image1-1.jpeg
image1-1.jpeg [ 109.04 KiB | Viewed 6252 times ]
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 Post subject: Re: Fet Amp not working
PostPosted: Wed Dec 12, 2018 4:16 pm 
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I think you have your LED in backwards. The long lead goes in the square hole, short in the round hole.

Take the chips out. What voltages are you getting on each pin? Put the chips back in. What voltages are you getting?

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 Post subject: Re: Fet Amp not working
PostPosted: Thu Dec 20, 2018 11:25 pm 
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Hi,
Yes the LED was in backwards. It works now thank you!

The following are the voltages tested on each pin from the solder side. in this order pin1-pin8


IC1 CHIP IN
8.05, 4.07, 8.02, 0, .01, 4.3, 5.49, 8.66

IC1 CHIP OUT
4.11, 4.10, 0, 0, 0, 4.26, 2.18, 8.66

IC2 CHIP IN
4.27, 0, 4.27, 0, 1.28, 4.25, 4.16, 8.09

IC2 CHIP OUT
0.28, 0, 0, 0, 0, 4.19, .35, 8.67

I'm not sure if i tested this correctly. A couple of pins started out at a high number and then bled off and stopped at a lower number. Is this common.
I have no idea what I'm doing when it comes to trouble shooting this thing.

Thanks for your help!


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 Post subject: Re: Fet Amp not working
PostPosted: Wed Jan 02, 2019 12:04 pm 
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Hi All,

I don't seem to be getting any responses so please let me know if I'm posting wrong on my end.

I wanted to add to the above post that I own an original Boss FA-1 FET Amp. I went ahead and tested it for comparison. It has the IC’s soldered directly to the board without sockets.
I’m not sure which chip is the tone or volume. they run horizontally so I’ll refer to them as top and bottom. Top being the input jack end.
When tested from solder side pin1-pin8:

TOP IC voltage tested
4.41, 0, 4.41, ground(0), 1.29, 4.46, 4.31, 8.71

BOTTOM IC voltage tested
4.32, 0, 4.32, ground(0), 1.29, 4.27, 4.32, 8.73

II appreciate any help you can send my way & please let me know if there is a better way to test this.

Thanks for your help, Kato


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 Post subject: Re: Fet Amp not working
PostPosted: Wed Jan 02, 2019 12:57 pm 
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Voltages look good with the chips out. Voltages look good for Chip #2. Chip #1 appears to be faulty. Swap the chips and see if the voltages change.

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 Post subject: Re: Fet Amp not working
PostPosted: Wed Jan 02, 2019 1:04 pm 
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Wish I had my FET Preamp here to check the voltages, but it's on my board at church. However, your Boss pedal voltages are very useful. Comparing them to your BYOC pedal suggests that either your IC1 is bad or something else in the build is screwing up the voltages. I suspect the former, since these old Hitachi op amps tend to have a fairly high failure rate. Your IC2 looks fine, since its voltages are almost identical to what you see in the Boss pedal.

Try this: Switch the two op amps in your build and take the voltage readings again. If the anomalous voltages move to the IC2 position, you've got a bad op amp and should contact BYOC for a free replacement. If the anomalous voltages remain in the IC1 position, then there's some other problem in the circuit that's affecting that op amp position.

EDIT: Well, at least Keith & I seem to agree on what's going on here! :mrgreen:

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 Post subject: Re: Fet Amp not working
PostPosted: Thu Jan 03, 2019 11:58 am 
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Joined: Tue Dec 11, 2018 7:00 pm
Posts: 5
Well, that's it!
I swapped the IC's and the voltage readings swapped too!
I'll contact BYOC about a replacement IC.
Thanks to all who participated in this adventure!

I'll be sure to post an update on this when I have one.

Cheers!


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