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LA502 Optical Compressor / 502 Compressor not working - test results.

« Last post by noeqplease on July 13, 2026, 04:16:31 AM »

Hi,

So one of my 4 LA 502 compressors did not work when first turned on. today I tested all the items on your handy troubleshooting list.

1. Checked for bad / cold solder joints, did not find any visible ones. Tested some different places on the circuit, and was able to get readings everywhere pretty much.
All ICs, transistors, and capacitors are in their correct orientations. No leads are near the chassis plate at all.

2. Checked DC voltages: + voltage is 16.14VDC, - voltage is -16.60 VDC. On TP1 I do get 1.105 VDC with the circuit bypassed, 1.04 VDC with the circuit engaged. So, there is some issue.

3. Applied a 1 VAC 1kHz signal to the input to follow it: Black probe on 0 V point.
R2 right leg reported 0.69 VAC
R 5 Right leg reported 0.025VAC with circuit in bypass, 0 VAC when engaged. REV 1.4
TP1 Reported 0 VAC, and no change when turning the GAIN knob.

So, something is definitely up. Please let me know what else I should test and how, so I can pinpoint the issue.

Thanks!!!

PS the other 3 compressors work beautifully.

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LA502 Optical Compressor / Re: R5 100K reads 26.6K after soldering it in... correct? DOC24

« Last post by noeqplease on July 12, 2026, 04:11:53 AM »

Thanks!

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LA502 Optical Compressor / Re: R5 100K reads 26.6K after soldering it in... correct? DOC24

« Last post by JPK on July 05, 2026, 06:12:28 PM »

This is perfectly normal, as this resistor is connected in parallel with several other components, which affect the resistance reading.

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First Aid / MOVED: True Grit (Kit) not working

« Last post by JPK on July 05, 2026, 06:08:00 PM »

This topic has been moved to True-Grit Tube saturator.

https://www.soundskulptor.com/forum/index.php?topic=7421.0

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True-Grit Tube saturator / Re: True Grit (Kit) not working

« Last post by JPK on July 05, 2026, 06:06:53 PM »

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SK49 Multi-patern Tube Microphone / Re: Shockmount elastic

« Last post by JPK on July 05, 2026, 06:04:23 PM »

We are going to purchase some spare elastic bands for shockmounts so we can supply our mic customers.
I will tell you as soon as available.

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LA502 Optical Compressor / R5 100K reads 26.6K after soldering it in... correct? DOC24

« Last post by noeqplease on July 05, 2026, 07:09:26 AM »

Hi all,

I am populating my first 502 compressor, and on one resistor, R5, which is 100K, after soldering it in, it reads 26.6K.

This is on DOC24, the version I am building.

Is this a normal reading for that? I know sometimes you can get mixed or different readings when things start getting connected around the circuit.

Thanks!

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True-Grit Tube saturator / Re: True Grit (Kit) not working

« Last post by guenter1910 on July 02, 2026, 08:52:08 AM »

I measured my way through the circuitry and discovered a broken link between C13 and R12. After fixing this everything seems to work fine. 

All the best
Guenter

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True-Grit Tube saturator / True Grit (Kit) not working

« Last post by guenter1910 on July 01, 2026, 05:23:50 PM »

Hi all,
I just finished the assembling of the true grit and unfortunately it is not working. The only thing that is working is the IN switch and the Blend Poti. All other switches and Potis have no function. I could measure the + and - 16 V on V+and V-. Also the tube is heating up.

Since I have not found any troubleshooting infos, I do hope to get support in the forum.

Any help is highly appreciated!!

Thank you in advance,
Guenter

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SK49 Multi-patern Tube Microphone / Shockmount elastic

« Last post by Alex Harmer on June 30, 2026, 11:53:50 PM »

Hi JPK,

I noticed the elastic band in the shockmount has started to wear, after one of the mics received a small impact. The shockmount did its job, and the mic is not damaged!

However, I would like to know where to get a new elastic band. Are you able to show me where? Or can I buy one from you?

Thank you,
Alex from NZ