Velodyne F1000b oscillation problem - Page 1
Forum section: electronics / repair

author: CHexclaim
author_rank: Regular Contributor
timestamp: September 23, 2019, 08:41:24 pm
content: Hello. I have an issue with a Velodyne subwoofer model F1000b that I need to solve for a customer.The issue is that the subwoofer starts oscillating at a midrange frequency (say between 500 and 1000 Hz) sometimes right after powered up and sometimes after a while.This sub has an accelerometer at the speaker and a feedback loop that aims to have a more controlled displacement given the relatively small power amplifier it has.On the web the only comments are that the electrolitics inside get bad and by replacing them it is sometimes solved.I did replace all the caps. Many of them were out of specs, but, although the behaviour is somehow different, this didn't solve the problem.I cannot find a service manual and would be great if someone has one.Any help is appreciated. Thanks!

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 23, 2019, 11:15:25 pm
content: Velodyne, another reputable pile of...I haven't repaired that many but haven't been impressed by the build quality.Some of them have the corrosive glue problem, if any of tour PCB's have component legs covered in the brown and crusty glue, scrape it away, it goes conductive and sometimes even crumbles component legs away.Other than that I can only remember a colleague mentioning a damaged sensor in a model with an accelerometer. Check glue first though...(Oh, and if I helped don't forget to donate)

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: September 24, 2019, 02:08:18 pm
content: Yes, these are magnificent as kindling, or even for a short full on blaze in the fireplace...

author: CHexclaim
author_rank: Regular Contributor
timestamp: September 25, 2019, 08:59:23 pm
content: I found some of the glue you mention on some VRs but it didn't seem have damaged the PCB. Anyhow, I removed it. It didn't solve the problemI fiddled with a VR which I believe it is located in the feedback loop and managed to stop the oscillation, but at one of the limits of the VR... It doesn't seem right.Thanks, CH

author: EHT
author_rank: Frequent Contributor
timestamp: September 27, 2019, 08:43:28 pm
content: You may find the old thread on this. I tried fixing one. The original fault was due to the failure of some sub-minature electrolytics in the power amp. Despite solving the original fault there was still unacceptable noise and distortion and the circuit was a royal pain in the arse to work on: glue everywhere, parts of the PCB very hard to access, high voltage un-isolated circuit.I stripped out the amp and am very happy with it as a passive speaker box. As it has speaker binding posts on it, the conversion is trivial. IMO its jut not worth the bother trying to 'fix' the amp. If I was purchasing a powered sub i would want one which has an external heatsink - many do. This is a ridiculous design to box in a "1000W" amp with no heatsink or airflow.Best regards

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 27, 2019, 10:31:05 pm
content: For a customer, so I doubt turning it into a passive is an option. Customers pay too much for this kind of pretty junk so they don't wanted munted during repair.