DSP-508A in Atari 1040STE

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BrettRogersUK
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DSP-508A in Atari 1040STE

Post by BrettRogersUK »

Hi All,

I've got a DSP-508A in my Atari 1040STE and the other day the fuse on it blew. It went bang (not a loud bang, but like a quiet bang (a fizzle really)).

Anyhow, I have received a recap kit for it and the dummy resistor loads are on the way for testing it. I also have some fuses (F2A 250v fast blow fuses) on the way too. These are the same fuses as the one that blew.

What I would like to know is would there be anything else on this particular power supply that you would look at changing out? the BU508 perhaps? Resistors? Diodes? Optocoupler? I don't want to put the new caps in and find that it still doesn't work properly.

I don't really know why the fuse blew as I had been using the Atari for some time before I started my upgrade of the TOS switcher, documented on here on the other forum.

Any help or info would be appreciated.

Regards,

Brett
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exxos
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Re: DSP-508A in Atari 1040STE

Post by exxos »

If the fuse has blown then I suggest removing the BU508 and testing to see if it is shorted or not. Generally it is the main driver shorted out which blows the fuse, or blown rectifier. Though the BU508 is a pretty robust device and I don't recall ever having one fail.
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BrettRogersUK
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Re: DSP-508A in Atari 1040STE

Post by BrettRogersUK »

exxos wrote: Mon Nov 29, 2021 8:56 pm If the fuse has blown then I suggest removing the BU508 and testing to see if it is shorted or not. Generally it is the main driver shorted out which blows the fuse, or blown rectifier. Though the BU508 is a pretty robust device and I don't recall ever having one fail.
Hi,

Thanks for that. Worst case scenario and I do have to replace the BU508A would this one (https://uk.rs-online.com/web/p/bipolar- ... rs/7146746) be suitable?

Thanks,

Brett
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Re: DSP-508A in Atari 1040STE

Post by exxos »

Yeah looks right at a glance.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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People should find solutions to problems, not find problems with solutions.
BrettRogersUK
Posts: 129
Joined: Wed Sep 15, 2021 12:48 am

Re: DSP-508A in Atari 1040STE

Post by BrettRogersUK »

exxos wrote: Mon Nov 29, 2021 9:54 pm Yeah looks right at a glance.
Thanks. All the figures look practically the same as what you posted on the guide for the DSP-508A on here. I'll have a look at the 508 anyway and do the tests you said to do to make sure it hasn't shorted before buying anymore.

Hopefully I won't need any more components for it and it'll work properly after the recap. I will also reflow the solder on all the other joints under the PSU board on all the other components just to be sure of no dry joints etc.

Again, thanks for all the help.

Regards,

Brett
BrettRogersUK
Posts: 129
Joined: Wed Sep 15, 2021 12:48 am

Re: DSP-508A in Atari 1040STE

Post by BrettRogersUK »

Hi All,

I think my power supply has given up the ghost. Most of the resistor values are not what they should be. One of them should be a 5.5k resistor and it's only reading 80 ohms.

So I think I'll just get a new power supply rather than risk putting this one back in after a recap. Hopefully they'll be available after Christmas. I might get a brand new Exxos power supply. I'm going to put it all away now so I can get ready for Christmas and clear my bench.

Thanks for all your help and advice.

Kind Regards,

Brett
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Re: DSP-508A in Atari 1040STE

Post by exxos »

Are you taking the resistors out of the board when testing them ?
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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BrettRogersUK
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Re: DSP-508A in Atari 1040STE

Post by BrettRogersUK »

Hi,

Yeah just out of interest I decided to check a few of them around near the fuse and output side. I've also checked them in circuit too and they gave the same values no matter in or out of circuit.

Regards,

Brett
BrettRogersUK
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Re: DSP-508A in Atari 1040STE

Post by BrettRogersUK »

Hi All,

I thought I'd give the resistors another check today and they came out bang on what they should be. So I don't know what was happening yesterday, maybe wasn't making good enough contact to get a proper reading. But I did today and the values were bang on.

So I thought I'd try recapping the PSU. Old caps came out with no problems and also the bridge rectifier as well. No problems. So put the new bridge rectifier in and all the other caps. Loaded the 2R2 dummy resistor onto the 5v line, and the 10R dummy resistor onto the 12v line. I also put a new fuse in as well.

Tentatively I plugged it and switched it on and BANG! Blew another fuse. So I tried again with another new fuse and again, BANG So definitely something wrong with it somewhere and definitely do need a new power supply 😭😭😭.

It looked like the bang was from the main transformer in the middle of the board, that's where a little puff of smoke came from. Around the area of the transformer, capacitor and two big grey resistors next to it. That's where it looked like it came from.

Regards,

Brett
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Re: DSP-508A in Atari 1040STE

Post by exxos »

Did you remove the BU508 and check if it's shorted out ?
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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