Comical contrasts - Page 1
Forum section: electronics / general

author: TerraHertz
author_rank: Super Contributor
timestamp: September 02, 2013, 11:38:33 am
content: What a day it's been!Started off with treading in cat poop while walking up the yard from workshop to house. So I stopped at the house corner tap to wash the shoe, and soooo... the TNT delivery driver who'd just been getting back into his truck out front after giving up on anyone being home, saw me. He had the first two parcels to arrive in my 'US re-shipper' experiment. Without the cat poop he'd have taken them away again, resulting in the usual failed delivery runaround.The parcels are all good. Clean and undented - they don't look even slightly like they were juggled by gorillas in a coal mine, which is the usual case with international shipping. One is some probes for a HP 8180A/8182A set. The other is a HP 3497A, that I'd bought just for parts. Particularly 'Option 001' which is an internal DVM card, that my working 3497A doesn't have.And so the second amusing event of the day. The HP 3497A is an 'acquisition and control system', that accepts plugin interface cards. Like many industrial controllers the cards have detachable wiring connector blocks, so you can remove cards for service without having to unscrew multitudes of wires. When buying these cards on ebay in the past, about half the time sellers have just pulled the connector block off the back of the 3497A, and try to sell the connector block as if it was the entire interface module. Unaware that the main card is still in its slot in the 3497A mainframe. The block has the part number printed on it, so I can see how a very very stupid person might think ebay listing it as that unit might fly.Well, that always made me grind my teeth. Because ultimately, it means the module has been destroyed - separated into two parts, unlikely to ever be reunited.So, what do I find when looking into the back of my newly arrived 3497A mainframe?Two interface modules, missing their connector blocks. Ha ha ha! It didn't occur to me I'd end up benefiting from this particular common stupidity. They are ones same as I have some of, so even if I can't find the blocks they're good for spare parts.And yes, it has the DVM card. And HP 4U rack brackets, which are kinda like hens teeth.The day wasn't finished with the ups and downs though.Next, some DRAM arrived that I'd been waiting a month for, to upgrade a PC. At last, hurrah!Wait... Hmm.... a seller in China who's whole business is DRAM, thinks posting the DRAM carriers (plain plastic) wrapped in plain bubble wrap, inside a bubble-padded envelope, is OK anti-static practice?Well it's not. Predictably one of the sticks is dead. I'd plugged all four in first go, and got the dreaded 'beepings of death' from the PC on power on. Proceed to the swappings, with one known good stick. Find one of the new four is bad. But here's the odd thing, that prompted writing this post. In slots 1, 2 and 3, it's so dead the BIOS can't start, but just sits there beeping. Put it in the last slot (with good DRAM in the other three slots), and something happens that I didn't think was possible in PCs. The DRAM is bad but the the BIOS doesn't detect it as bad, and tries to start. With this comical result:

author: sleemanj
author_rank: Super Contributor
timestamp: September 02, 2013, 11:55:40 am
content: Quote from: TerraHertz on September 02, 2013, 11:38:33 amUnfortunately, many (not all though) of the Chinese sellers who only sell electronic components more often than not just don't give a crap even if they do have any knowledge.My favourite was a bunch of ICs sent plugged into a scrap of quite normal polystyrene, which was breaking apart, only holding together by it's static charge, and all wrapped with cling film.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: September 02, 2013, 11:58:01 am
content: The standard PC memory POST doesn't cover the working space required by the BIOS itself, as you have just discovered.

author: TerraHertz
author_rank: Super Contributor
timestamp: September 02, 2013, 12:47:44 pm
content: Quote from: ElectroIrradiator on September 02, 2013, 11:58:01 amPOST uses workspace in the top 1 or 2 GB of 4 GB DRAM? I don't think so. But I am curious how this screen corruption happens.Actually I thought the very early stages of POST used just CPU registers and cache, which is how come it can generate beeps despite no working DRAM at all.Also supposedly with all four DRAM slots occupied the machine should be running in dual memory channel mode. Don't know if it is or not.It's a HP-Compaq DC7700p / DC7700 SFF desktop. CPU: Intel Core2 6300 @ 1.86 GHz.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: September 02, 2013, 01:08:41 pm
content: Quote from: TerraHertz on September 02, 2013, 12:47:44 pmI don't recall the exact details, but this is what I learned last time I looked into testing RAM modules. The POST is rather crude, and doesn't even test every block of every RAM module. This is why a module may pass POST yet show errors inMemTest86.

author: amyk
author_rank: Super Contributor
timestamp: September 02, 2013, 02:18:23 pm
content: Quote from: TerraHertz on September 02, 2013, 12:47:44 pmIf it's a chipset with integrated graphics part of the DRAM will be mapped as VRAM, and I guess the POST memory test doesn't touch that.And as those who've used memtest86 will be familiar with, the POST memory test is not particularly thorough.

author: Unknown
author_rank: Unknown
timestamp: September 02, 2013, 03:42:54 pm
content: I wouldn't want the POST to take as long as memtest86 on a modern system with a decent amount of RAM, though. I think merely sampling some random blocks and checking if they can be written and read is fine for a POST.

author: c4757p
author_rank: Super Contributor
timestamp: September 02, 2013, 03:49:08 pm
content: I think it would be acceptable to keep a counter in nonvolatile, and do a full check of every byte everynPOSTs. Or even do a partial check every time, but alternate sections so that the full RAM is tested in total after a certain number of POSTs.memtest86 exercises the RAM very carefully, so it takes a long time, but even with a lot of RAM, a modern DDR2/DDR3 system could stuff it all and read back in a few seconds with efficiently written code.

author: SeanB
author_rank: Super Contributor
timestamp: September 02, 2013, 06:20:18 pm
content: Post Ram test is basically just looking at page boundaries for the existence of memory that will accept a write, a read and a check of inversion. Nothing fancy, basically checking how big the RAM is. i have some HP printer dimm sticks that are 86MB, not 64 or 128. but 86MB. Weird that, they must have been buying semi faulty chips and only using the ones with a good bottom half.

author: peter.mitchell
author_rank: Super Contributor
timestamp: September 03, 2013, 10:29:45 am
content: Quote from: TerraHertz on September 02, 2013, 11:38:33 amHave you tried starting Wandows Ngrmadly?