twin cobra no boot black srceen

PCB problems and fixes
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salahithe1
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twin cobra no boot black srceen

Post by salahithe1 »

Hi all bought some pcb's off of ebay the guy said he did not no if they would work. Well one of them was twin cobra. I pluged it in fingers crossed i got a black screen help what to do next please. :(
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Re: twin cobra no boot black srceen

Post by davewellington »

Got a Logic Probe?
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salahithe1
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Re: twin cobra no boot black srceen

Post by salahithe1 »

No i have not. Just started collecting pcb so a noob :(
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davewellington
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Re: twin cobra no boot black srceen

Post by davewellington »

Pretty much if you don't have the basic repair equipment, you're better off sending the board to someone else to repair. Check the bottom of the Repair Guide page for some contacts.
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salahithe1
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Re: twin cobra no boot black srceen

Post by salahithe1 »

Could it be that the voltage could be to low on my new asrto city. As it says on wiki that some older games need more voltage.
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davewellington
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Re: twin cobra no boot black srceen

Post by davewellington »

Don't adjust it if you don't have a multimeter to test it though.
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salahithe1
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Re: twin cobra no boot black srceen

Post by salahithe1 »

Ok then should be patient and wait to i get the basic stuff to perform these tests then. :(
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Re: twin cobra no boot black srceen

Post by kdoe »

Well, there's a really useful section on the wiki here telling you how to do basic troubleshooting on pcbs. Although to do anything you need a multimeter and to do anything really interesting you'll have to at least buy a logic probe or later maybe a scope, eprom programmer, etc.

FWIW The last game I had that booted to a black screen had a bad connection to the crystal and therefore no clock to the CPU but your problem could be totally different.
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salahithe1
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Re: twin cobra no boot black srceen

Post by salahithe1 »

Hi what do you mean by bad connection to the crystal explain to me please.
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Re: twin cobra no boot black srceen

Post by trmatthe »

salahithe1 wrote:Hi what do you mean by bad connection to the crystal explain to me please.
There will be either a crystal in a can or an oscillator which will produce the clock that the CPU and the rest of the board needs to make things happen. The logic chips on a PCB all tend to work in a synchronous method, as in they all work in parallel and take new input and provide new output at the same time (this is a bit of an over-generalisation in many ways but is good enough for the question).

If the crystal has a dodgy connection then it won't be able to vibrate and generate the tiny electrical pulse which is used to trigger everything on the board. However, unless you've got a logic probe or scope (or maybe a high-impedance speaker) then you're not going to be able to tell whether the crystal is working.

Normally when you have an unknown board fault you'd check that you're getting power, then you'd pick the main CPU and check it has power and a clock signal (which is obviously derived from the crystal) and that the /RESET line is working properly. If you don't have power then the CPU can't run, if you don't have a clock then the CPU will sit there and do nothing, and if you have a dodgy /RESET signal then the CPU will probably keep cycling, or never starting.

But basically you need some test equipment - at the minimum a logic probe and a multi-meter to measure voltages.
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Re: twin cobra no boot black srceen

Post by trmatthe »

This is what a can-type crystal will generally look like http://ram-e-shop.com/test11/popup_image.php?pID=1311 Often the can is a lot shorter - only a half centimetre or so.

And this is what an oscillator generally looks like http://ram-e-shop.com/test11/popup_image.php?pID=189

The difference between the two is that a crystal (also known as xtal) needs external circuitry to generate a clock signal, whereas an oscillator only needs power and then produces a ready to use clock.
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Re: twin cobra no boot black srceen

Post by salahithe1 »

Thanks for the input aswell as the pictures very helpfull. Now to start buying equipment to start fixing pcb boards :D
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Re: twin cobra no boot black srceen

Post by trmatthe »

No probs. What country are you in? Can suggest some links if you're UK or find you some ebay items if elsewhere. And you should fill in your location field anyway :)
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salahithe1
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Re: twin cobra no boot black srceen

Post by salahithe1 »

Hi am from sunny southend essex uk :D
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