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Asteroids test rig

Printed From: ukVac.com
Category: Technical
Forum Name: Tech, Maintenance & Repairs
Forum Description: Need Help? Ask Here
URL: http://www.ukvac.com/forum/forum_posts.asp?TID=359873
Printed Date: 20 Nov 2017 at 6:46pm


Topic: Asteroids test rig
Posted By: grobda
Subject: Asteroids test rig
Date Posted: 13 Sep 2017 at 6:29pm
I've borrowed an AR2 and a power brick for my asteroids test rig but now (after a few years) am thinking its time to give it back.

So I'd like to use a switcher and an AC transformer, (something like http://www.farnell.com/datasheets/1821925.pdf" rel="nofollow - this ) and I'm concerned about a couple of things;

1. How much current does the 36VAC transformer need to supply?

2. Common Ground - the transformers I'm looking at are twin 120v input and twin 18V output, my understanding is that I connect the inner poles of the two primaries together and the outer poles to mains. Then wire the two inner poles of the secondaries together and connect that to the ground of the switcher, and use the outer poles of the secondaries to supply 36VAC to the PCB.

3. Does the circuit need anything else? Looking at the wiring diagram from asteroids it doesn't look like it, but never hurts to check.

Definitive answers appreciated before I blow something up. 


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sporadically obsessed with this sh*t



Replies:
Posted By: Mitchell Gant
Date Posted: 13 Sep 2017 at 8:41pm
Originally posted by grobda grobda wrote:

1. How much current does the 36VAC transformer need to supply?

100mA should do it, it's only driving some op-amps and the 5V DAC supply (about 10mA each).

That transformer you linked isn't large enough though!

Originally posted by grobda grobda wrote:

2. Common Ground - the transformers I'm looking at are twin 120v input and twin 18V output, my understanding is that I connect the inner poles of the two primaries together and the outer poles to mains. Then wire the two inner poles of the secondaries together and connect that to the ground of the switcher, and use the outer poles of the secondaries to supply 36VAC to the PCB.

Yes that is correct. Just make sure you box it well (preferably plastic) and fuse it on the primary. Also best to connect mains earth to your 5V -ve ("ground" of the switcher you called it). That should stop the outputs floating up above mains earth potential.

Originally posted by grobda grobda wrote:

3. Does the circuit need anything else? Looking at the wiring diagram from asteroids it doesn't look like it, but never hurts to check.

I don't even supply 36VAC to my test rig. I use a dual output DC power supply and it works OK on +18V and -18V to the AC inputs. Only thing there is that is doesn't truly test the rectifier diodes CR9-12. But if they're duff and you feed it AC you'll have some smoke anyway... I've never seen any of those faulty myself, but doesn't mean it can't happen! Good practice should be test the diodes first before plugging in to your test rig. I really ought to practice what I preach though! Embarrassed

If you just want to test the logic and don't need to see video or sound output you can just feed it 5V and probe away on the watchdog reset and vector HALT lines, that will test all the CPU section and a chunk of the vector generator. You soon learn what a faulty one looks like with the watchdog reset flashing or the vector HALT stuck.



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Boy, is this a machine!



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