weirdocollector

Fantastic job! Does this uses the old SDRAM on board of the Nabu pcb, or its own internal VRAM?

Hi! One of my 1351 mouse ha stopped working in the horizontal direction and looking at the IR leds through my smartphone, it looks that the corresponding IR LEDs do no light up indicating that at least one of them has gone KO. Is there a modern substitute for those LEDs ? Thanks for any help.

Thanks for the suggestions ! I also assumed that the machine were starting and initialising correctly but with no screen. During the test I just left on the DVP the metal bar that was fixed with two screws on the PCB metal shield: would that be enough or should I have to attach it back to the shield and test again ? I've tried with another VDP (an NTSC one) but without any change besides the on screen colours. What do you suggest to use to check the RAM chips ? I would like to be able to identify which one are failing without having to change them all. Thanks again.

OK, last post... I've had another try connecting the keyboard, and after turning on the TI and hearing the beep when I press the space bar and then '1' (to start TI BASIC) I'm greeted with an orange rectangle. This behaviour seem to be consistent, repeating itself at every boot. Again, thanks for any help!

Just checked the voltages on the DRAM chips. Everything seems to be ok. Now when I power on the TI I just get a light blue screen and a single beep. Some vertical traparent columns are visible on screen. Hope this helps.

Just another question. Is this surely a DRAM problem or it can be caused by another faulty component? When I remove the DRAM chip I've socketed nothing cahnges and the same garbage is displayed. Also the VDP should not be the culprit, as I swapped it with another one with no effect. Thanks again.

I've piggybacked another chip on each of the other 4116 but nothing changes. I'll try to measure the voltages as soon as I can get back to the TI99 Thanks again.

Hi! I just changed one 4116 chip accordingly to the instructions only and pictures on the Ninerpedia page that pointed to the bit 3 chip as defective. If I remove the new chip I've replaced and socketed the garbage screen do not change. What voltages should I check ? The ones on the DRAM chips? Thanks for your help.

Hi! Today I took the time to attempt to repair one of my TI99/4a which, judging from the screen displayed and according to this Ninerpeia page (https://www.ninerpedia.org/index.php?title=Troubleshooting) implied a defective 4116 chip and precisely the one corresponding to bit 3 (no TI logo and text and coloured squares of the wrong colours).. I replaced and successfully socketed a new DRAM chip without any issue and without damaging any PCB trace, and after turning on the computer everything seemed OK as the logo and the text were displayed as expected. But unfortunately it didn't last for long and after about a minute the screen passed trough increasing states of degrade and now just display utter garbage accompanied by random beeps. I've attached the sequence of degrading screens displayed by the TI99 after the apparently successful repair... I've swapped both the DRAM chip the VDP (my machine is a PAL one and as I only got some TMS9918 I got the same garbage with a pink background) but to no avail. Curiously even if I remove the DRAM chip from the board, nothing changes and the same garbage is displayed on screen. I really do not know what is happening as everything seemed at first OK after changing the DRAM chip. Have anybody experimented something similar ? Any help will be really welcome. Thanks a lot in advance.

Thanks to everybody for the precious help! I've just ordered some DRAM from a reliable source ?

Thanks for the advice. I'll try first to piggyback a 4164 to the one pointed out in the troubleshooting guide to see if the problem persist.

If I press '1' when being in the blank screen with just the two coloured stripes I'm sent to a blank screen. When I do the same while the characters are disappearing from the start screen I can see the text of the BASIC screen fading away in the same way of the one on the start screen leaving me with the same blank screen.

HI! After a long time, yesterday I took my two TI994a out of the closet and while one of them functioned perfectly, the second showed a strange video behaviour. When first turned on, the image is perfect and both the stripes of colours, the TI logo and the text appear as expected. After a few seconds the image starts to degrade as the logo and the text begin to fade away pixel by pixel, leaving just the two coloured stripes with the wrong colours (see attached photos). If I live the computer off for a minute this behaviour repeats with the image being perfect at the start and corrupting after a while. Turning off and on the machine without waiting brings back the two wrongly coloured stripes. Consulting this troubleshooting guide (https://www.ninerpedia.org/index.php?title=Troubleshooting) is seems that the problem may lay in the third VRAM chip as the corrupted screen depicted for Mask 11101111 corresponds to the one displayed by my TI994a. What really baffles me is the fact that the video corruption does not manifest immediately when turning on the machine but appears slowly pixel by pixel and on the text and TI logo only. Is that a sign that the real culprit may be the VDP and that the VRAM chip is not to be blamed ? Have some of you experimented the same feat ? Thanks a lot for any help!

Thanks Bruce! A real treasure trove Thanks again.

Hi! I've recently 'discovered' the Coleco ADAM and I've found a fascinating machine I'm now trying to collect as much technical info as I can, but I cannot find anywhere the source code files (I understand that binaries are the ones used by MESS) of the ROMs of the various 6801 processor used by the ADAM. I've found the PDF with the same code, but having source files would be very handy. I've already searched the forum, but the link to the archive with these files (http://drushel.cwru.edu/6801/6801_src.zip) does not work. Can anyone send it to me in a PM, or give a working link? Thanks in advance for any help.