Overheating chip on Atari STE plugged into socket U405--is it normal?

Troubles with your machine? Just want to speak about the latest improvements? This is the place!

Moderators: Mug UK, Zorro 2, spiny, Greenious, Moderator Team

Post Reply
jmprice314159
Atarian
Atarian
Posts: 4
Joined: Tue Jun 05, 2018 6:15 pm

Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by jmprice314159 »

Hello all,

Chip on Atari STE plugged into socket U405--is it normal for it to get quite warm? About the same temp as the 68K CPU. Not too hot to touch, but warmer than the other chips. The reason I ask is I replaced a dead PSU with a Centurion PSU, and one of the capacitors on the PSU gets quite hot to the touch, and it cannot be a faulty PSU as I tried it in my STF and the capacitor does not get hot. I bought the STE on Ebay and it had a dead PSU.

The 4MB ram banks also are warm.

Any thoughts on the temp for U405? Should it be as cool as the other chips, or around the same temp as the 68K CPU? Not so hot as scorching or anything close, but def hotter than other chips. The main concern I have is whether the PSU is going to burn out. Perhaps that is what caused the original Atari PSU to die.

Thanks,

Jason

jmprice314159
Atarian
Atarian
Posts: 4
Joined: Tue Jun 05, 2018 6:15 pm

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by jmprice314159 »

Couple of other questions:
What does the chip in socket U405 do?
Can it be replaced with a newer part?
If yes, what is the part number?

Thanks,

Jason

neanderthal
Obsessive compulsive Atari behavior
Obsessive compulsive Atari behavior
Posts: 122
Joined: Sun Jul 10, 2016 10:58 pm

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by neanderthal »

Well U405 handles main clock switch(32Mhz) and mono mon detection and is a standard scottky (S) so might get warmer than the other around TTL stuff.CPU and Dram sim banks generates some heat so dont think you have anything to worry about if everything works as supposed to.About the PSU cap, you have to ask centurion about that(I never tested one).Must admit cant remember if U405 gets hotter or not?..My exprimental STE had that one replaced(busted it due to testing) and using some low power chip (Ls,HCT or something),,btw folks dont do that for one has to add a pullup if using other versions.(mono mon detect gets wonky)

User avatar
dhedberg
Atari God
Atari God
Posts: 1135
Joined: Mon Aug 30, 2010 8:36 am
Contact:

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by dhedberg »

What capacitor on the PSU runs hot? Capacitors should not run hot. Electrolytic polarized caps can if the polarity is reversed or if the specs of a cap do not meet the requirements.
Daniel, New Beat - http://newbeat.atari.org.
Like demos? Have a look at our new Falcon030 demo and feel the JOY.

jmprice314159
Atarian
Atarian
Posts: 4
Joined: Tue Jun 05, 2018 6:15 pm

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by jmprice314159 »

atari_psu.jpg
It is the capacitor that I've placed some pennies on. See picture.
You do not have the required permissions to view the files attached to this post.

User avatar
dhedberg
Atari God
Atari God
Posts: 1135
Joined: Mon Aug 30, 2010 8:36 am
Contact:

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by dhedberg »

Doesn't seem right. That's an electrolytic capacitor and I see no reason why it should become hot unless its damaged, the polarity is incorrect or it's exposed to ripple currents that's outside of its specifications, etc.

In general, electrolytic capacitors should not be exposed to high temperatures and they should not generate a lot of heat. When their temperature increases, their ESR value (resistance) increases as well, resulting in more heat generation. It affects the life span of the capacitor. You could try and replace the capacitor with one that has a lower ESR value. It will handle ripple current better. The Panasonic FR series of electrolytic capacitors are excellent for this purpose.
Daniel, New Beat - http://newbeat.atari.org.
Like demos? Have a look at our new Falcon030 demo and feel the JOY.

tzok
Captain Atari
Captain Atari
Posts: 204
Joined: Fri Jun 30, 2017 7:22 pm
Location: Bielsko-Biala, PL
Contact:

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by tzok »

It is better to fit there a 74F254. Mono detection already has a 4k7 pull-up (R472).

neanderthal
Obsessive compulsive Atari behavior
Obsessive compulsive Atari behavior
Posts: 122
Joined: Sun Jul 10, 2016 10:58 pm

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by neanderthal »

R472?,,oh you thinking about the select signal for U405 there,pin 3 on monitor connector.
Pin 4 on connector (pin 2 and 6 on U405),were the ones I had to use a pullup on when used a HC something since those tend to float
when not connected.

User avatar
mpattonm
Hardware Guru
Hardware Guru
Posts: 491
Joined: Mon Oct 21, 2002 8:52 am
Location: Czech republic
Contact:

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by mpattonm »

dhedberg wrote:Doesn't seem right. That's an electrolytic capacitor and I see no reason why it should become hot unless its damaged, the polarity is incorrect or it's exposed to ripple currents that's outside of its specifications, etc.

In general, electrolytic capacitors should not be exposed to high temperatures and they should not generate a lot of heat. When their temperature increases, their ESR value (resistance) increases as well, resulting in more heat generation. It affects the life span of the capacitor. You could try and replace the capacitor with one that has a lower ESR value. It will handle ripple current better. The Panasonic FR series of electrolytic capacitors are excellent for this purpose.
Thats what I told Jason in privat comm. The PSU is overloaded, there is something fed up on the mainboard.
BTW the 2200uF caps used on this series of STPSU, are Nichicon UPM1C222MHD6 .
Last edited by mpattonm on Sun Sep 15, 2019 7:23 pm, edited 1 time in total.

tzok
Captain Atari
Captain Atari
Posts: 204
Joined: Fri Jun 30, 2017 7:22 pm
Location: Bielsko-Biala, PL
Contact:

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by tzok »

Oh yes, I missed that. Pin 4 is mono detection and is left floating.
As for pull-ups I believe it is a design flaw, and despite of chip version being used, there should be a pull-up resistors on both monitor input pins (3 & 4). It is not recommended to leave input pins floating. BTW this is a gen-lock circuit.

neanderthal
Obsessive compulsive Atari behavior
Obsessive compulsive Atari behavior
Posts: 122
Joined: Sun Jul 10, 2016 10:58 pm

Re: Overheating chip on Atari STE plugged into socket U405--is it normal?

Post by neanderthal »

tzok wrote:Oh yes, I missed that. Pin 4 is mono detection and is left floating.
As for pull-ups I believe it is a design flaw, and despite of chip version being used, there should be a pull-up resistors on both monitor input pins (3 & 4). It is not recommended to leave input pins floating. BTW this is a gen-lock circuit.
Yea,,there are a couple of misses,however could be the gen-lock idea that made them leave out pullup(tho could used a high vakue one)
since it will be running clock injected there.
Fun thing ,dont think I ever seen anything doing gen-lock on STE.

And a question,has anyone tested overclocking the system thru there?
Not that I believe one can do any significant overclock and video freqvencies will be skewed so more of a academic question.

Post Reply

Return to “Hardware”