Comparing visual differences between two PCBs - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: August 31, 2017, 11:43:42 pm
content: Not being an EE or expert in the field, I'll ask this question of you guys who will have a better trained eye than I do.I'm looking to purchase this device (it's just a SCSI to SD card adapter). There are two versions designed by the same guy, slight difference in price, however it looks like they come from different fabrication/assembly companies. The red PCB had a second revision to increase the space between some solder pads (apparently it was a bit of an issue) however the green PCB was not revised as it didn't suffer from the same problems even with the smaller spacing (possibly better manufacturing processes?)Attached is a photo of both PCBs (the red one pictured is the revised version). Can anyone see any obvious advantages/disadvantages of one over the other? Any differences in the brand/quality of the components?There are additional images on each of the online stores:https://www.itead.cc/scsi2sd.htmlhttp://store.inertialcomputing.com/SCSI2SD-p/scsi2sd-v5b.htm

author: sleemanj
author_rank: Super Contributor
timestamp: September 01, 2017, 12:20:02 am
content: I would hazard a guess that "increase space between solder pads" is maybe in reference to the QFP, the green one maybe had the soldermask removed as a block over the entire of each of the 4 sides because there wasn't enough space between pads to get a soldermask finger in there, and the red one might have had the pads slimmed down so the soldermask can go between.This affects manufacturing, soldermask between pins means it's less likely to form a bridge, without soldermask between pins bridging is a lot easier (on a fine pitch package like this).

author: wraper
author_rank: Unknown
timestamp: September 01, 2017, 12:46:54 am
content: Boards use the same components. Except red board have 2 oversized fuses F1, F2 which are wider than pads. But that does not mean the board you'll get will have them too.

author: Halcyon
author_rank: Unknown
timestamp: September 01, 2017, 09:55:29 am
content: Thanks guys, I figured there was very little difference between the two, but I just thought I'd ask just in case there was anything glaringly obvious to those who design PCBs etc...

author: macboy
author_rank: Super Contributor
timestamp: September 01, 2017, 07:12:46 pm
content: I see a set of terminating resistors on the red one that are missing in the green one. Since you are using SCSI I am sure you are painfully aware of the importance of proper termination.

author: wraper
author_rank: Unknown
timestamp: September 01, 2017, 07:35:25 pm
content: Quote from: macboy on September 01, 2017, 07:12:46 pmOr fail see the same resistor networks but of black color.

author: macboy
author_rank: Super Contributor
timestamp: September 02, 2017, 12:02:57 am
content: Quote from: wraper on September 01, 2017, 07:35:25 pmOn closer inspection, you are right. That socket isn't empty.Regardless, to use or not to use these cheap passive terminators is still a question of bus topology - the speed of the bus, and what else is on the bus and where.

author: Halcyon
author_rank: Unknown
timestamp: September 02, 2017, 01:05:03 am
content: Quote from: macboy on September 02, 2017, 12:02:57 amIt's not going to be too much of an issue, these boards are designed for old Apple, Amiga, Atari and other vintage computers which used SCSI disks. The bus speeds weren't incredibly fast (compared to more modern SCSI).

author: tooki
author_rank: Super Contributor
timestamp: September 02, 2017, 06:34:41 pm
content: Yeah, the Macs that used onboard SCSI had buses designed for passive termination (except for the oddball Mac IIfx, that needed a special terminator, though I don't know what was different about it). Some vendors did indeed sell active terminators, and in normal use made no difference, but occasionally were able to solve SCSI voodoo.