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Author Topic: Q*bert. A man and his grail... FINISHED !!!  (Read 171949 times)
Nic-fryer
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« Reply #195 on: January 21, 2015, 09:53:16 AM »

I love detailed threads like this, it means that if I ever come across an arcade machine I know what I'm doing Smiley
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« Reply #196 on: January 21, 2015, 10:06:23 AM »

Great, that's one of the reasons I write this stuff.....and also for my own future reference Wink

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« Reply #197 on: January 21, 2015, 03:33:54 PM »

Been thinking about "solving" the heat issue on the power board.

So we have to "get rid" of at least 18Volts of energy.....that's a lot really !

The solution IMHO should have some important aspects:


- must work without problems
- solve the heat issue
- be cheap
- use as few (extra) components as can be
- the less mods on the board the better

The first thing I thought about was using a voltage regulator instead of the zener diode.

This would be possible, here's an example schematic:


HOWEVER, the problem with this is that whichever way you turn it, the whole thing _still_ needs to "get rid of" (offical word: dissipate) 18Volts....so the heat is going to exist anyway because the LM317 is a lineair voltage regulator....

The one thing I don't know is wether a set-up like this will heat up as crazy in unloaded condition...if not, this would be a good idea.

Then I googled a bit more, and found out that there are beefier versions of the LM317, like LM150 and LM350, which are basically the same but can provide currents up to 3 Amps.

The Q*bet manual claims that the 30VDC section is designed to deliver 1.5A so that would be more than sufficient.

The best thing is that the LM150/350 come in a TO-3 housing so......could I put that on the spot of the 2N3055 ??

Well yes I could, but I'd have to mod the board/connections because the pins don't match (Vout is the case on the LM, but that's the Collector on the 2N3055, essentially I'd have to swap the case connections and one pin. I already thouhg of a clever and easy way to do that but.....read on)

OK, so if would really be pretty easy to do this mod, you'd have to remove the zener and put a pot there instead and bridge the input resitor. A second resistor would have to be put in between Vout and the reference voltage pin....could be done.

However, again , these are still linear regulators, and the amount of heat produced would still be the same ! The big advantage though, is that the heat will be pumped right into the heat-sink.....

I don't know how hot the heat-sink normally becomes, but seeing that the black is totally gone on my heatsink I guess it does get pretty hot.




The next idea I played around with was finding a cheap "buck" DC-DC switching converter and "hacking that in". It wouldn't look pretty, but it would GREATLY reduce the heat because switchers of course have efficieny of up to 95%....

So I searched and searched, but there don't seem to be any of these devices that AND can handle 2 Amps, AND can handle 50V input AND put out +30V......


Then I thought....why can't we take away the SOURCE of the problem, being the rather high 48VDC "source" voltage after the rectifier ?

Of course, I cannot change anything about the 35VAC coming out of the transformer (unless I'd use an extra transformer, but that's not the way I want to go)
Since the AC-DC conversion is done by the usual (and efficient) diode-bridge set-up (=full wave rectification) couldn't I go back to something basic and use only 1 diode do we'd get a half-wave rectifier.
Usually you don't want half-wave rectifiers because they waste half the energy, but that's about what we're after here Smiley

The problem with this idea however is that the ripple will be much higher with half-wave rectification and usually audio amps don't like that (or you can hear it).....

In my basic idea the voltage _would_ be (about) half of the 48V, so a nice 24V. This is definitly enough for the LM379 sound amp (minimum power voltage is 10V) and the knocker might be a little bit weaker but not much....

Now I wonder if the two filter caps of 2200 (in parallel, so 4400uF) would be enough filter for half-wave rectification.

I guess there's only one way to find out.....try it and give my oscilloscope some good use Wink



In the mean time, if wiser electronic buffs then me have any opinions about this, please chime in (after you stopped lauging about my stupid ideas Wink)
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« Reply #198 on: January 22, 2015, 06:55:56 PM »

Woohoo, saturday 40% off on all color mixed paints at Karwei !!!!

and I'll be taking the cab Bruno style......


* image.jpg (121.68 KB, 2009x413 - viewed 318 times.)
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« Reply #199 on: January 23, 2015, 12:03:28 AM »

OK.


Call me puzzled.

I went the half-wave rectifier way.

I removed diodes D21 and D24 (well, soldered them loose on their cathode side, which is the same thing)
I shorted D23 with a jumper wire. This hooks the - to the return of the transformer 35VAC line.

So only D22 would still do something (very important), rectifying only half-wave...at least I thought...

I first thought I might have to remove some of the regulating stuff but though it probably wouldn't matter.....so I switched it on, and luckily no smoke and a nice +30V LED on.

I measured the output and got a neat 30VDC. However, I had anticipated the "input" DC voltage across the filter caps to be about half of the normal 48V.

However, when I measured there I got.....47V !!!

I don't get it !
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« Reply #200 on: January 23, 2015, 12:11:42 AM »

In the mean time, I decided to forget about the filter board and hook up the harness straight together.
Easy but tedious work.

This is the result:


* IMG_1997.jpg (679.38 KB, 2584x910 - viewed 362 times.)
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« Reply #201 on: January 23, 2015, 12:12:29 AM »

That's 66 points of contact less that could possibly cause trouble....


There's still one more plug to do, but that's the cable to the monitor....gotta dig up the new one....


* IMG_1998.jpg (590.04 KB, 2420x673 - viewed 358 times.)
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« Reply #202 on: January 23, 2015, 12:39:00 AM »

Well while I was having the PSU board set up anyway I figured I could just as well also hook up the soundboard. Now it was very handy that the speaker panel can easily be removed from the cab. However, as mentioned the volume pot was missing so I had to hack a small pot.

The results were as follows:

http://youtu.be/THX53AnQoXo
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« Reply #203 on: January 23, 2015, 01:04:26 AM »

the suspense in that clip is killing!    Cheesy

nice one!
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« Reply #204 on: January 23, 2015, 07:20:13 AM »

Do you have the schematic?


OK.


Call me puzzled.

I went the half-wave rectifier way.

I removed diodes D21 and D24 (well, soldered them loose on their cathode side, which is the same thing)
I shorted D23 with a jumper wire. This hooks the - to the return of the transformer 35VAC line.

So only D22 would still do something (very important), rectifying only half-wave...at least I thought...

I first thought I might have to remove some of the regulating stuff but though it probably wouldn't matter.....so I switched it on, and luckily no smoke and a nice +30V LED on.

I measured the output and got a neat 30VDC. However, I had anticipated the "input" DC voltage across the filter caps to be about half of the normal 48V.

However, when I measured there I got.....47V !!!

I don't get it !
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Laszo
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« Reply #205 on: January 23, 2015, 08:12:47 AM »

Well while I was having the PSU board set up anyway I figured I could just as well also hook up the soundboard. Now it was very handy that the speaker panel can easily be removed from the cab. However, as mentioned the volume pot was missing so I had to hack a small pot.

The results were as follows:

http://youtu.be/THX53AnQoXo
you sure it is working? I could only make out Yessss and ..... Sounds good....   Grin
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anunaki
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« Reply #206 on: January 23, 2015, 08:33:55 AM »

nice, I clearly hear @!#?@!
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« Reply #207 on: January 23, 2015, 08:38:34 AM »

nice, I clearly hear @!#?@!

Aaaahhhh is it supposed to do that  Tongue
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« Reply #208 on: January 23, 2015, 10:21:51 AM »

Turn up your hearing-aids old men because what it says is: "Hello, I'm turned on"


 Grin Grin Grin

And when I press the test button you hear a tone.

This doesn't guarantee the board is 100% though, there could still be things wrong. This board is a computer on its own with a 6502 and 6532. I should be able to trigger some more sounds by shorting some inputs but I haven't found out which yet....

The good news is that it at least does the basic things and that the voice synth chip and LM379 amp work OK.
« Last Edit: January 23, 2015, 10:38:12 AM by Level42 » Logged

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« Reply #209 on: January 23, 2015, 10:56:45 AM »

Here's the schematic Leo.

As mentioned, I removed diodes D21 and D24 (well, soldered them loose on their cathode side, which is the same thing) and I shorted D23 with a jumper wire.



* image.jpg (67.39 KB, 1417x273 - viewed 321 times.)
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