Powder Coat Resistance Issue (Solved)

[mightydob]

Hi all,

After a very enjoyable few slow weeks taking my time building the Crack which is my first DIY audio project, I completed the build and started checked the resistance readings last night.  All were perfect apart from terminal 8 which continued to show 1 on my multimeter.

A pure guess form my point and as highlighted in the title is this might be because the Powder coating I had applied is causing resistance on the plate.  I did check if this would be a problem before building it but a few post seemed to indicate that they had no resistance issues, therefore I did not remove any of the coating when attaching the components.  I have since read recommendations to scrape the powder coating off a key points which is no problem but I wanted to check a few things first.

1. Is my analysis correct? is there a way I can test this before scraping the coating or is it that obvious  that this is my problem
2.  At which points should I scrape, all of the points where I am putting screws into the plate?  Should I just start with the Safety ground and take the reading again or for safety and other future issues should I do it on others e.g. Octal socket, terminal strips.  The screws for the 9 pin socket were very tight after powder coating so probably will have cut into the powder coating anyway.  I'm really pleased with how everything looks so obviously don't what to remove things unnecessarily.

Thanks in advance for replies, please let me know if you need any more info.

Thanks 

[Rocketman248]

How are your other readings?  There's nothing actually attached to terminal 8, so I don't believe it's too crucial (someone please correct me if I'm wrong).  The ones you want to be concerned with are the various ground connections.

[mightydob]

Hi, All other resistance readings are perfect, I have not started the voltage checks yet because I'm new to all of this and the manual said not to proceed if a terminal was listed as 0 and measured 1, and the voltage checks scare me a bit anyway

[mightydob]

Fantastic thanks both, I will get on testing the voltage

[fullheadofnothing]

Actually, the fact that 8 doesn't read 0Ω points strongly to there being a problem. The only route to ground terminal 8 has is through the chassis. Most likely, the 1 you are reading is actually the way your meter reads over limit. You have probably isolated your chassis from both safety and signal grounds. You are reading 0Ω on the other grounds because they are wired together. If terminal 3 is not connected to the chassis, that could be a source of noise, and isolating the safety ground lug from the chassis could leave live voltage on the chassis in the event of a mishap.

[Paul Birkeland]

I agree with Josh.  You should measure DC resistance between the "E" terminal of the IEC power entry module and terminal 3.  You want very low resistance between these terminals.  (And you want continuity through the chassis, adding a piece of wire between the two defeats the purpose)

[mightydob]

Hi all

Doh! I thought I was all okay, I completed the voltage checks and all was spot on, lucky I checked back here.  I have just checked the resistance between the earth on the power entry and terminal three and its reading 1, so I guess I have a problem 

Am I on the right lines about scraping the powder coating off?  And if so is the Safety ground the most likely issue?

Cheers

[fullheadofnothing]

Yes, scraping the paint off will fix the issue. The safety ground absolutely needs to be scraped, as does the front terminal strip (terminal 3).

[mightydob]

Thanks

Went for it anyway before your reply as it seemed logical and success! I scraped the Safety ground and I now have a 0.02 resistance between the power entry earth and terminal 3, so as I guessed the screws which attached the 9 pin socket were tight and have bit into the paint anyway (unless you think I should scrape it anyway?).  There is still no resistance on terminal 8 but I know what to do now so I will attempt the scraping on there but its all a bit more wirey around there so will probably wait until tomorrow.

No rush anyway since I've been building this away from home and I left my 650's at home so I have an agonising wait to listen to the Crack until Friday anyway

Thanks ever so much for everyone's help, truly fantastic support.  Hopefully I wont need it when building the Speedball in the near future

[Paul Birkeland]

Don't worry about terminal 8, it doesn't really serve any electrical purpose.

-PB

[mightydob]

Even better!

Thanks again