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Old 13 May 2019, 13:56   #1
project23
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Join Date: Jul 2018
Location: Liverpool
Age: 36
Posts: 427
A quick tip for TF530 builders

Hey, I know we're not really advised to build this thing and should instead be building the 534, but as I already had all the parts for the 530 I thought i'd give it a go before ordering a 534 PCB.

The reason I make this post is that I made a very stupid mistake in building the 530 that took a lengthy trawl over the board in Eagle for me to spot. The mistake is critical and renders the board non-functioning.

I've documented it here because I noticed a lot of other people in the various threads over the months talking of the same issue (good soldering, no shorts, but black screen on boot). I'm sure most of those issues come back to solder bridges and the like, but if there's a chance one person has made this mistake then I thought it best to at least mention it - as embarrassing as it may be

See, the solder mask on some of these boards isn't particularly good. If you've bulk-ordered your parts then you'll note you have just one value of 0603 cap. There are three places on the board where it seems reasonable to put these for, i imagined, bypass reasons.

Except there are two places. Not three.

Next to the ram CPLD is a small pad for 'RCLKLOAD', though on my 530 this is difficult to see.

This line goes straight to the clock. Placing a cap here is a very bad idea. The symptoms are an obvious ripple on the 3v3 line and a non-functioning card.

I removed the offending cap and the thing booted first time into diagROM.



A simple enough mistake, but given that RCLKLOAD isn't required, so not listed on the BOM with any particular value, it is quite easy to assume it is another bypass cap -perhaps related to SPI.

Again I know this is now a depreciated card, but if there's anyone out there who has a dead 530 in their drawer who made this silly mistake, then it might be worth getting it out and fixing it up.

John
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