Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-20, 19:37

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Eep386 wrote on 2021-05-20, 18:12: Dumb Q perhaps, but did you try squirting some contact cleaner into the ROM sockets? Not a dumb q. But yah. Did that. Even used the good stuff, dexoit d5

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-20, 00:46

by

by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ugh. Jeezus So i put the original bios in, and its still not doing anything. its been consistently givng me those beep codes but now now. I havent changed anything but still reseated everything. Nothing. powers on but no bios beeps at all.

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-20, 00:11

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The sellers usually send their stuff to center including from Chinese sellers. This is why I'm rather cautious and you have to verify what sellers are from. It is the big, expensive, popular brands that Amazon seize the fakes but not all got escaped the bag. Cheers, Yah i do mixed reviews from this …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-19, 23:47

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

These were shipped with Amazon prime, so the address is just the center they shipped from. I did do a verify after writing, shows successful. I also burned with with the changes, and without (they actually sent 2 roms) but either way, notta, same response as if the Bios isnt even in the machine. Im …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-19, 23:03

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Were the chips from chinese sellers? Cheers, Dont think so. Got them on amazon. (Which i know means nothing) however i tried to remove any "paint" with some alcohol for the lettering and nothing came off. Usually with fake or rebranded chips it starts to smear off from my experience (which is …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-19, 21:30

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Well.. I got the new eprom in today, made the change to the Last byte in the bios, and it burned ok. However, when i boot now with the new bios, it dont even beep. Blanked the chip out with UV, and reburned, same thing. So one thing i noticed on the chip, is the original chip is a M27c512 15-F1, and …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-18, 17:38

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Alrighty, correct eprom has been ordered. Should be here tomorrow. I think there is a way to use the larger eprom, but ill just be patient and wait 🤣 Again Thank you!!!

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-18, 14:29

by

by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Omg your right. Doh. Oof, and i ordered the wrong size chip too. Hurray 🤣

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-18, 00:46

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Deunan wrote on 2021-05-18, 00:20: Yes, except now you have a wrong file (or no file) loaded since it's full of FF, the last byte should've been 00. Thats how the file goes It ends in some 00's, but then starts FF's

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-18, 00:01

by

by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Sorry, Been a Long Day 🤣 Like this? 😀

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-17, 23:59

by

by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ah ok! That was the last 00 i saw, so the last FF is where it will be. So basically change the last FF to 5D

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-17, 23:08

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I appreciate your help in all this. so please thank you again. I got some eproms that should be arriving tomorrow, and I think i see what you mean.. heres a screenshot of what im looking at Basically I highlighted in red the last 00 i see, so i wanna change that to 5d? (i notice on the "output " …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-17, 00:31

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

So the VGA BIOS looks OK - I mean it's a bit weird that it's header says it's only 24KiB long, but the checksum does match that entire area, so it's unlikely be a coincidence. Now the mobo BIOS doesn't pass the checksum test, but possibly it's not calculated the usual way. I'd have to disassemble …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-16, 20:40

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Don't use the programmer software checksums, you don't know what and how they calculate. Maybe it's 16-bit or not even a checksum but CRC. Just write your own script to calculate that. Or post the mobo BIOS image here. As for VGA BIOS, just like any other BIOS extension it has to follow specific …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-12, 22:22

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

My Rom Reader came in today. It appears to be able to read the Bios just fine. I created a dump of it. There is also the VGA bios, and that seemed to read ok and i created a dump of that too. Not sure what I am really looking at in the software, the last bit on the bios seems to end in 00, and the …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-11, 01:24

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

BIOS extensions (like video card BIOS, SCSI, etc) have rules - you can look that up, but the mobo BIOS itself can do it in any way, or even not check at all. Typically though the checksum is computed by adding all the bytes of the image and the result should be zero (that is, after masking it to …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-10, 23:30

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by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Do you have access to an EPROM programmer? Dump the BIOS, the checksum can be tested in the binary image. This would at least tell you if the image is corrupted (and so the chip has failed) or is it a mobo problem. I will on wednesday. I bought one. Ive been kinda wanting one for some other …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-10, 20:40

by

by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

For the life of me I cannot find the bios files. I was able to find a startup disk online however, that wont help me since it wont even post. I know its kinda rare for the bios chip to just up and fail, but the bios itself is just an eeprom with a label on it, so im wondering if those just dont last …

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Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-10, 01:45

by

by 90skidJohnny

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Just picked up a Tandy 4825SX off ebay, in non working shape. Always wanted one of these, and even in non working state, its a thing of beauty. Upon power up, I got 6 total beeps (1 Beep, Long pause, 1 beep long pause, then 4 pauses with short pauses) which to me on the list of tandy beep codes I …

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Re: Monitor Questions! Trying to use a Tandy VM-1 With a TRS-80 Model 1 - Questions on sync and other Fun stuff!

Posted on 2020-11-01, 21:31

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by 90skidJohnny

in Marvin \ Video

in Marvin \ Video

Dunno about most, but for that time period probably yes, since most of those machines like the Model 1 and Apple IIc were designed for TV scan rates anyway. No idea about a tube swap - I'd expect that most of the difference is actually in the electronics, not necessarily the tube itself. But it'd …

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