AMD AM2950 - Page 1
Forum section: electronics / general

author: Wawavoun
author_rank: Regular Contributor
timestamp: April 21, 2023, 08:53:38 pm
content: Hi,I recently got a Microsoft Z80 Softcard II for Apple II. It looks the board works but more tests to follow.On this board there is a AM2950 chip. They get hot...I dont know what it is and his purpose. I try to find a datasheet but without success...Anybody has information about this component ?Regards.Philippe

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 21, 2023, 08:55:41 pm
content: https://en.wikipedia.org/wiki/AMD_Am2900

author: Wawavoun
author_rank: Regular Contributor
timestamp: April 21, 2023, 09:00:13 pm
content: Thanks !I look to the page.The chip is briefly mentioned as 8 bits i/o port but there's no more data so no way to know if this heating is normal.

author: Benta
author_rank: Super Contributor
timestamp: April 21, 2023, 09:10:24 pm
content: If you didn't burn your finger, it's normal.ICs used a lot of power back then... and that one's a bipolar.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 21, 2023, 09:17:29 pm
content: Quote from: Wawavoun on April 21, 2023, 09:00:13 pmYes, the heating is normal, unless it is so hot that you can't keep the finger pressed on it.40-50*C was considered "normal".

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 21, 2023, 11:28:46 pm
content: Quote from: Wawavoun on April 21, 2023, 09:00:13 pmThis series of ICs being based on bipolar (not CMOS) transistors, it was certainly drawing significant power, so not really surprising they run hot. As long as it appears to work and no smoke escapes, you should be fine.This one is a bus transceiver so nothing really fancy. You can find a scan of the datasheet here:https://www.datasheetarchive.com/pdf/download.php?id=753bec59ce3feae52b655da3ec2b09c7d98f5c&type=M&term=AM2905

author: Wawavoun
author_rank: Regular Contributor
timestamp: April 22, 2023, 06:25:39 am
content: Re,On another forum someone post the datasheet ! Hereunder joined.He draw more than 200 mA alone ! He can be hot...No smoke and the board work but leave the finger on the component was over my pain resistance... So say over 50 °C !In my Apple 2e I have this board, a Chat Mauve Eve and the floppy interface. I cant find all the information about current consumption for all these boards.The technical manual say that the power supply has 500 mA (on the +5 V I guess) capacity reserved for extensions...Is there a risk the power supply be overloaded ?Regards.Philippe

author: RoGeorge
author_rank: Super Contributor
timestamp: April 22, 2023, 08:03:05 am
content: Most of the power supplies have protection against too much current drawn (the protection against short-circuits). It was not uncommon for a board to draw between 1A...5A, depending of how many IC were on it. You can estimate by counting the normal TTL chips + look in the datasheets for the larger chips.Hard to say without seeing the board, can you attach a picture of it?What power supply do you have, or want to use?

author: Wawavoun
author_rank: Regular Contributor
timestamp: April 24, 2023, 07:28:17 am
content: Hi all,I experience crash and hangout with this computer when I use this Z80 board. They come always during floppy read-write...The current on the 5 V rail is ~2.4 A without floppy works.Is it possible that this increase during floppy r/w operations over the limit and then crash the computer ?Regards.Philippe

author: RoGeorge
author_rank: Super Contributor
timestamp: April 24, 2023, 08:21:57 am
content: Yes, a floppy drive has at least one stepper motor that will produce current peaks while making steps.Check with an ESR-meter that any electrolytic filtering capacitors are still in good shape (and not dried out). Electrolytics on the supply lines act as small local energy tanks that will supply the extra current bursts needed by whatever circuit is nearby the electrolytics. If they have lower than nominal capacity, or if they have high ESR (Equivalent Series Resistance), they won't be able to supply peak currents, so all the other circuits will see a drop in voltage at each current peak. This can make a computer crash.1. - make sure you have thick wires to the power supply2. - wires must be copper, not the chinese iron wires (often terminated with alligator clips), iron wires are not good, you can detect them with a strong magnet, if your power supply wires are magnetic, replace them with thick copper wires.3. - not nice to ask only, without reading/answering the questions

author: Wawavoun
author_rank: Regular Contributor
timestamp: April 24, 2023, 11:29:17 am
content: Point 3 - You are right !I see your reply but I must admit that opening the Apple II, extract the boards take pictures, make the transfer to the computer, reduce resolution because too big for the forum etc has make me step back...And when I can provide value to a thread I reply...The Apple IIe psu I use is a unmodified standard one.I have a PC power supply with all the required voltages and with a lot more power. I will make a test...Thanks for the advices.Philippe

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 17, 2023, 04:15:49 am
content: If the PSU is an original one and has never been serviced, wouldn't be surprising if some caps in it had just dried out. The opposite would be. So certainly test with another supply first.After that, you can always repair the original PSU.