xrbrevin

rooting through my bits looking for a 16k RAM board, i found this: i thought i'd try and power it up but i need ROM chip A105. i know an EPROM can be used for the XL/XE models but can i use one for this? also, can anyone identify the modded RAM board? crikey, im getting a crash-course in 400s at the moment - its great fun! thanks in advance ?

offer him $50 and see what he does ?

thanks for clarifying that, every day is a learning day ?

To ascertain the cost, we would need advice from someone who has had the same problem In the image below, the ANTIC chip is on the bottom row, second from the left. Some 800XL chips are in sockets so they are very easy to lift out. If you are up to it, open yours up and see. It may just fix it for free ?

Ive only got my 400 rigged up at the mo but pressing CAPS once will make the letters lower case. To put them back to upper case i have to press SHIFT and CAPS. If i press CTRL and CAPS i get the various ASCII symbols instead of letters. Try SHIFT and CAPS and see if it reverts back to normal. if not, i think there may be debris or damage causing the unwanted conductivity

Kjmann mod completed and looking good! Here's the details: I used this guidance: But i couldnt get the exact values so i bought 20x 510ohm, 240ohm and 120ohm. I metered them all up and found ones that matched as close as poss. I also decided to take the ground connection from an area nearby to these (see the black wire below), so as to keep all the wires as grouped up as poss. it also allows the power PCB to be removed without any fuss. I used an old USB cable as it is 4-core - its ideal and fits the cable guide castings with same tension as the original. i also added the 75ohm resistor (the one with red heatshrink tubing below) to the luma signal. i dont have any 22uf tantalum capacitors so i havent added anything to the chroma signal. anyhoo, here is my creation: I didnt need to drill/file the EMF shield, the wires exit nicely just above the screw-hole when the base plate is screwed on. I refitted my PAL power PCB as the RF modulator is removable via a pin header and it is now removed. this negated the requirement to cut the 2x tracks as stated in Kjmann's guide. At the other end of the (now ex)USB cable, i soldered a female 5-pin DIN socket - like what is supplied with the Super Colour CPU Card from TF_HH. Here are the results! These photos don't do it full justice, i need a gimbal!! The audio is nice and loud too - i never knew you could just tap the POKEY pin 37 directly. ? So i'd recommend it to anyone, very cost effective and high quality results. the fiddliest bit was soldering the DIN plug! (pesky things...)

if it was software related, i.e. something you pressed, then it would revert back to normal when powered off and on again. for this reason, im thinking it is hardware related and it just happened to fail when in use. ive never heard of a function like you describe but maybe others have? what model of atari is it?

try swapping over the POKEY chips. POKEY controls the keyboard and the audio so maybe its the common denominator?

The ANTIC chip contains the character set. If you can, remove the chip and reseat it, in case of a dirty contact. Failing that, try one from another machine

its worth trying another screen if you can

Further to my post #226 - i forgot the stamped number: NTSC model with SCCC and 48k/52k expansion S/Nos Printed: AV 385051 Handwritten: AV 132681 7/23 Stamp: Atari / 302

further to my post #225 - i forgot the stamped number: PAL model with RAM board modded to 32k S/N: 050 008702 G Stamp: Atari / 501

here are 2x variants of the service manual for the 800 R204 is related to pin 4 of the RF modulator. Is this how you are connecting it to a display? If so, can you try a monitor cable (composite or svhs)? Sams_Computer_facts_Atari_800.pdf Atari_400_800_Field_Service_Manual_June_82.pdf

wow thanks for all the informative feedback. it was from ebay / china and the pins look suspiciously grubby. it could well be a dud. i will pull one from a working drive and see if it helps diagnose it. i just thought that seeing it only cost a quid fifty it was worth a shot. maybe it is a sh*tty-shot...! (groan) with the old RIOT installed, the self-test seems to pass ok. then powering the Atari the SIO polls the drive fine - it spins up as it should but slow beep boot error follows. i tried pushing down lightly on the head and also applying pressure to push the head back and forth on the rails but i get no reading beeps. i think it may be component-fail related. time to swot up using the FSM and the Sam's manual methinks

Hi, I recently attempted to fabricate a track display for the 1050. I managed to get the zero to work and also to increase the track number but further meddling caused the drive to malfunction. So I ordered a replacement RIOT 6532 chip. It arrived today and when I fitted it, all the drive does is spin the drive motor. I get the slow boot error. I understood this chip to be like the PIA - i.e. an off-the-shelf part. Does anyone have any experience of replacing this? Maybe there are variations and I ordered the wrong variant? Here is a pic of the ordered one, thanks in advance!

cartridge games were a bit of a rarity when i was a nipper so i have a soft spot for them these days. im grateful to the guys who convert games so i can PCB them, 3D print a case and label them up. they look great! ?

Star Raiders also bypasses the ROM so its also useful for diagnosing a dodgy OS IC

many thanks to you all - i think the Kjmann mod is the least intrusive and i will give it a go asap! i will have to root through my resistors & caps this eve. i just got a laptop screen to replace, a TV inverter and a win8.1 black screen to sort first... (yawn) then i can do the 400 ?

is there a summary/guide available? cheers

NTSC model with SCCC and 48k/52k expansion S/Nos Printed: AV 385051 Handwritten: AV 132681 7/23

PAL model with RAM board modded to 32k S/N: 050 008702 G

as per the link in my 1st post, i lifted R164 and connected the remaining luma/chroma signal to the composite in on my screen - see 2x pics. the result is no good. i also lifted R171 to separate luma and chroma but still no good. (is composite comprised of a mixture of both of these or just one?) ...so there is more to it than that. other articles have used the 2600 composite mod with successful results (this seems the least invasive: http://blog.tynemouthsoftware.co.uk/2018/10/atari-400-composite-video-mod.html?m=1) so maybe the 400 is missing some amplification circuitry. maybe atari left these out knowing they wouldnt be needed in an RF modulator arrangement? anyhoo, i then connected the lifted side of R164 to audio-in on my screen but no joy there neither as a secondary issue, this 400 had no audio at all when i got it so i checked out the various resistors and reflowed a few joints but still no audio. i popped the lid off the RF modulator and saw a charred looking cap but there was nothing i could do to make the audio work. i then dug out my other 400 (NTSC variant, fitted with the SCCC) and it has a different modulator on the power board - i.e. not connected via a 5-pin header. so i switched the entire power board between the machines and voila - it now has audio! ? the NTSC 400 doesnt need the modulator as it has the SCCC so both are fully functional. the NTSC modulator required the screen to be retuned to channel 3 but the image is pretty decent for an RF signal - see pic.

Most 800XLs do not have the chroma signal connected at the monitor port. Thus using S-Video means you dont get any colour, just a sharp monochrome display. A simple mod can resolve this tho. Later model 800XLs that use a 'Freddie' chip do have the chroma signal but they are much less common.

tf_hh also has a 512kb SRAM expansion that fits the 800XL: http://www.van-radecke.de/STUFF/tfhh_HW_info.pdf

a lot of expansions/developments were planned for the XLs but Atari got sold to Jack Tramiel who immediately axed lots of projects despite their advanced progress. (Check out Curt's Atari Museum for further info) His motivation was to reduce costs and increase profit margins so the XE line came out soon after with its reduced manufacturing costs. Atari had previously been run with heart but Tramiel now made the decisions with his head.