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Old 20 September 2017, 12:19   #201
PeteAU
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Quote:
Originally Posted by kinmami View Post
Hello Guys
First of all congratulation for the project development and shared time.
I have written a BOM list draft where the highlighted items need your confirmation regarding the nominal value of some components and the suggested length of socket pins.
In attachment.
Thanks
IMO C3, C6, C23, C11 are not needed - I run happily without them. Pads are there just in-case.

C13/C19 are alternatives. Only one of them is needed. Any value >=4.7uF will be fine. 2.2uF ceramic also good.

C20 is also a bit optional - it might be a good idea on a power hungry expanded machine. Your choice looks fine.

U6 - Should be "F", "HCT" or "AC" only. Your choice is CMOS and probably won't work. Back in the 1980's, AMRAM boards used 74LS and it still worked.

I don't think DIP48 socket will fit. Maybe DIP24 twice will. Most people use 2.54mm pin strips instead.

For the pins to mobo: https://www.aliexpress.com/item/Sing...535232012.html
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Old 20 September 2017, 13:28   #202
Mq666
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I confirm C3, C6, C23, C11 are not needed.
I don't use C12 and C19 too. I'm soldering 100nF as C13 for decoupling RTC. I don't solder any big tantalum or ceramic too, but I'm soldering electrolitic capacitor C20 instead of that. I use electrolitic 100uF - I'm sure it's more than enought, but I have a lot of them so I use them - I think it could be 10uF too.

Second matter: Yesterday I built provisional DRAM chips tester.
I attach pictures.
I don't have SOJ42 sockets, but I use SOJ40 sockets from old VGA cards.
I cut one side of sockets so DRAMs can be fitted inside them.
On the last two pins of DRAM there is +5V and GND duplicated with pins on the opposite side. I measured that they are internally connected in chips, so I left them not connected and it works.
In sum I solder 4 sockets, C1, C4, C7, C22, U6, C16 and wirings - that's all.

Tester works stable, and now I can check DRAM chips before I solder them into target extension. I did this device, because I had issues with bad DRAM chips previously, and now I have to build 5 more extensions, so it will be easier.
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Old 20 September 2017, 20:41   #203
kinmami
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Thanks.
Revised list, based on your suggestion and Digikey P/N availability, in attachment.
Attached Files
File Type: zip A500 trapdoor memory exp free design REVISED.zip (15.1 KB, 16 views)
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Old 20 September 2017, 21:31   #204
Mathesar
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Quote:
Originally Posted by Mq666 View Post
It looks like extension randomly will work or will not work with the HCT. My friend tested 74HCT74, 74F74 and 74ACT74, and Gary adapter don't work with HCT for him. With ACT and F it works fine.
I think 74HCT is risky, so I solder 74F only, and I recomend to use F series, because F series has shorten propagation delay.
I used all HCT logic in my build without any problems. The '139, '00 and '74 are certainly not timing critical.
The two '00 chips that generate the new regen and ramen signals "might" be critical. Otoh, like Pete said; the original amram boards used LS logic...

Where do you source your logic and RAM chips? I source my logic from a dutch webshop and the ram from salvaged simm sticks. I did not use any eBay parts.
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Old 20 September 2017, 21:50   #205
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I got logic chips from Digikey and Mouser and ram from AliExpress following PeteAU's recommendation.
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Old 20 September 2017, 22:16   #206
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Quote:
Originally Posted by kinmami View Post
Thanks.
Revised list, based on your suggestion and Digikey P/N availability, in attachment.
Hey, great !! Thanks

Maybe PeteAU can take a look again and give his OK? Some changes in b6 regarding the bom ?

@Mq666
I had the same idea, if i'm going to start the project maybe i'll order the right sockets. Sockets matching perfectly
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Old 20 September 2017, 23:41   #207
Mq666
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I bought all my logic in F series from local internet shop, which is good and tested many times, and I haven't any issues with them. HCT series checked by my friend was from old stock which he has.
All DRAM chips I have from old SIMMs. I checked them all in old PC before I desoldered them.

But now it is something interesting.
With my tester I checked some DRAMs today. I have NPN chips which all works perfectly. I have 16pcs of them.
But today I desolder some LGS chips from another SIMM - same as I have in my very first extension which had issues described in the beginning of my "RAM extension adventure".
And I have same issues with them! Three chips works perfectly in each order. But four chips give me various issues in various chips order. In one order I have yellow screen, in other order I have random errors, in yet another order last chip RAM is unvisible. I exchange chips between them, and I found one order in which everything works perfectly.
I think this chips has some critical parameter value which may cause incompatibility.

I did a lot of confusion in this forum thread. I'm sorry if someone is annoyed by this.
Maybe none of you will ever reproduce my problems, because maybe they only concern specific chips, from a particular manufacturer and from a specific series.
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Old 21 September 2017, 22:44   #208
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Thanks for info about the LGS chips . Maybe you can post a detailed picture with this LGS chip.
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Old 22 September 2017, 11:36   #209
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Quote:
Originally Posted by Mq666 View Post
I don't use C12 and C19 too. I'm soldering 100nF as C13 for decoupling RTC. I don't solder any big tantalum or ceramic too,.
Just 100nF for the RTC isn't enough. When you flick the power switch off, the voltage on the RTC briefly dips way down (around 2V) and it will sometimes forget time/date. I watched it on a scope. It really needs a few uF on C13 or C12.
Alternatively you could make R5 smaller to let the battery drive harder during these events.

Quote:
Originally Posted by kinmami View Post
Thanks.
Revised list, based on your suggestion and Digikey P/N availability, in attachment.
-For D1, BAT721C is better due to lower Vf.
-IMO I think you should delete C14,C15,Y1 and recommend only RTC62421/RTC62423/RTC72421/RTC72423.
-And of course R6 & LED are optional.

Let us know if "A412-ND" fits, I wonder if it will.
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Old 22 September 2017, 12:18   #210
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Quote:
Originally Posted by PeteAU View Post
Just 100nF for the RTC isn't enough. When you flick the power switch off, the voltage on the RTC briefly dips way down (around 2V) and it will sometimes forget time/date. I watched it on a scope. It really needs a few uF on C13 or C12.
Alternatively you could make R5 smaller to let the battery drive harder during these events.



-For D1, BAT721C is better due to lower Vf.
-IMO I think you should delete C14,C15,Y1 and recommend only RTC62421/RTC62423/RTC72421/RTC72423.
-And of course R6 & LED are optional.

Let us know if "A412-ND" fits, I wonder if it will.
updated.
pls review and let us know.
thanks
Attached Files
File Type: zip A500 trapdoor memory exp free design REVISED.zip (17.0 KB, 10 views)
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Old 22 September 2017, 13:15   #211
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additional update in attachment.
waiting your kind comment.
thanks
Attached Files
File Type: zip A500 trapdoor memory exp free design REVISED2.zip (17.2 KB, 14 views)
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Old Yesterday, 01:44   #212
PeteAU
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Quote:
Originally Posted by kinmami View Post
additional update in attachment.
waiting your kind comment.
thanks
My only comment is that's too expensive. The sockets, connectors and RTC could be much cheaper elsewhere.

P.S. I have posted rev B.6 (1st page). This should be finished for 2017
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Old Yesterday, 03:48   #213
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Quote:
Originally Posted by PeteAU View Post
My only comment is that's too expensive. The sockets, connectors and RTC could be much cheaper elsewhere.

P.S. I have posted rev B.6 (1st page). This should be finished for 2017
unit prices & P/N from digikey are just for reference.
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Old Yesterday, 13:30   #214
Mq666
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Quote:
Originally Posted by PeteAU View Post
Just 100nF for the RTC isn't enough. When you flick the power switch off, the voltage on the RTC briefly dips way down (around 2V) and it will sometimes forget time/date. I watched it on a scope. It really needs a few uF on C13 or C12.
PeteAU, You're right. My mistake. I was wrong because I misread the schematic. I have mistaken a group of capacitors C10, C11, C20 with a group C12, C13, C19. I was thinking that electrolytic C20 is doubled with tantalum we talking about. But not. Ok, now I corrected extensions I have, by solder 10uF as C12. Thank You for the tip.

Katarakt: My problematic LGS chips are same as on that picture:
picture
It's actually not my picture, but I have same chips, but my are 9805, 9806, 9807.
I have eight chips like that. I was coupling one set of four chips working properly together and one set of three chips working properly together too. But there is only one working combination. Each other combination had issues. Eighth chip don't works at all, because one day he works great and another day he causes yellow screen. Rest of chips must be in one order that I found working. Exchanging chips to other order causes random errors in last fourth chip as I described in previous posts in this thread.

I don't have more LGS chips, so I leave it as it is.
Any other chips from other manufacturers working great and without any issues for me.
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Old Yesterday, 14:44   #215
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Thanks Mq666 and PeteAU for rev. b6
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