daafies Posted June 28, 2015 Share Posted June 28, 2015 (edited) hi all, i recently bought faulty model 4 from ebay. its in really good condition, other then i get a screen full of characters when i start it up. also the disk drive spins a bit and stops. its a non gate array, with 64K here's what i tried so far: 1) i reseated all the ICs, 2) checked the motherboard for cracks and lose connections/soldering. eveything there looks ok. 3) checked voltages from power supply. i get like +4.9, 11.9 and -11.9 4) rearranged the memory ICs 5) i tried break+reset, enter 2x and typed "out 244,1" + enter but no drive activity just now the while typing the power suppy filter caps went up in smoke lol. very exciting. could one use a more modern power supply like an ATX? i have an old dell one here with +5, +12, -12 ? any ideas what i should try next? new CPU? thanks very much in advance! Edited June 28, 2015 by daafies Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 28, 2015 Share Posted June 28, 2015 Does the screen come up the same every time or does it change every time you turn the machine on or reset it?If it's the same, did changing the order of the RAM change the screen.If the screen stays the same and changing the order of the RAM chips changes the screen, I'd say it's bad RAM.If the screen changes every reset, then maybe the CPU.There are many other things that could be wrong though. Quote Link to comment Share on other sites More sharing options...
daafies Posted June 28, 2015 Author Share Posted June 28, 2015 Does the screen come up the same every time or does it change every time you turn the machine on or reset it? If it's the same, did changing the order of the RAM change the screen. If the screen stays the same and changing the order of the RAM chips changes the screen, I'd say it's bad RAM. If the screen changes every reset, then maybe the CPU. There are many other things that could be wrong though. screen is pretty much same with every reset. i dont recall if it changed with the RAM chip reorder. i'll have to check again. i can also change the screen with holding the break key at power up. what RAM chips should i get? old stock? or is there new equivalent i can use? and on the power supply caps. can i use mylar film? i got NTE caps here laying around that meet the .01uF and .22uF. MLR103k630 and MLR224K630 thanks! david Quote Link to comment Share on other sites More sharing options...
daafies Posted June 28, 2015 Author Share Posted June 28, 2015 screen stays the same. also after rearranging the RAM chips. maybe RAM is ok then? possibly Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 29, 2015 Share Posted June 29, 2015 screen stays the same. also after rearranging the RAM chips. maybe RAM is ok then? possibly Maybe, maybe not. A bad ROM *might* be consistent, bad RAM *might* be consistent in spite of the chip order... it's probably not the CPU. Turning it off and on should alter the display if the RAM is ok and the CPU isn't writing junk to it due to a faulty ROM. I rarely see ROMs go bad. Are any of the RAM chips hot to the touch? Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 after running for ~15mins: z80 = 130F PALl6L8 (U59) = 129F PAL16R6A (U3) = 120F PALl6L8 (U4) = 120F MCM68A316E Character Generator (U23) = 122F ram chips are 95F ish (not hot to the touch) Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 the rest is below 120F. btw the serial card is disconnected. Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 i added some pictures of the screed. the smaller fonts are when you turn on the computer normally i get the larger fonts when i hold any of the funtion keys and power on the machine. (i also here a click. relay maybe?) holding break and powering on doesnt result in anything different. Quote Link to comment Share on other sites More sharing options...
Omega-TI Posted June 29, 2015 Share Posted June 29, 2015 ? Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 sorry i didnt 'finish' uplading the photos. they should be there now.. btw how do you attach something like you did? it'l only allow me to add an image by URL? Quote Link to comment Share on other sites More sharing options...
Omega-TI Posted June 29, 2015 Share Posted June 29, 2015 There are multiple ways... the first, a direct link to your image in a gallery like this... Or like how you did it... Or by clicking on the "More Reply Options" button and uploading it from your PC. Quote Link to comment Share on other sites More sharing options...
Omega-TI Posted June 29, 2015 Share Posted June 29, 2015 Hey... I like the TI-99/4A on the left-hand side of the photo! Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 29, 2015 Share Posted June 29, 2015 (edited) Really, it doesn't tell me much except I think the CPU is running since it changed to 32 column mode.Every other character is displayed in that mode.I can also tell that all of the bits are set for some of the graphics characters to it's not necessarily a problem related to a single bit in video RAM somewhere. However, I think that A (whatever accent character that is) is supposed to be a blank from clearing the screen.That could still be video RAM or some data logic between the CPU and video RAM.*edit*Keep in mind, it could also be the character generator circuit but I think something would show up on screen like it was asking the normal startup questions on the Model III.Cass?Memory Size?If you hit enter a couple times does the display change? Edited June 29, 2015 by JamesD Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 There are multiple ways... the first, a direct link to your image in a gallery like this... Or like how you did it... Or by clicking on the "More Reply Options" button and uploading it from your PC. aha! more reply options. cool thanks for that! Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 Hey... I like the TI-99/4A on the left-hand side of the photo! yes trusty ol' 99 is running just fine Quote Link to comment Share on other sites More sharing options...
Omega-TI Posted June 29, 2015 Share Posted June 29, 2015 yes trusty ol' 99 is running just fine Speaking of your TI... how about taking a photo or two and placing them in << THIS THREAD >> ? Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 Really, it doesn't tell me much except I think the CPU is running since it changed to 32 column mode. Every other character is displayed in that mode. I can also tell that all of the bits are set for some of the graphics characters to it's not necessarily a problem related to a single bit in video RAM somewhere. However, I think that A (whatever accent character that is) is supposed to be a blank from clearing the screen. That could still be video RAM or some data logic between the CPU and video RAM. *edit* Keep in mind, it could also be the character generator circuit but I think something would show up on screen like it was asking the normal startup questions on the Model III. Cass? Memory Size? If you hit enter a couple times does the display change? :/ no hitting enter a number of times has no effect. but who knows enter key could be bad too i tried the enter key on number key pad also. assuming it does the same thing Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 29, 2015 Share Posted June 29, 2015 My first guess is RAM or a ROM issue. Without being able to directly mess with it, it's a bit difficult to diagnose further. Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 i reseated the roms again and now get this: sorry for the rotated pics and vid Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 My first guess is RAM or a ROM issue. Without being able to directly mess with it, it's a bit difficult to diagnose further. i understand. thanks for the help James. do you nkow a source for ROMs and/or RAM? cheers david Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 29, 2015 Share Posted June 29, 2015 (edited) The block diagram in the tech manual shows data buss and address buss buffers. If you can find those, reseat those as well.That's looking very much like a ROM issue. Did you check the drive controller to see if it's chips are seated ok?*edit* That's definitely not video RAM. Edited June 29, 2015 by JamesD Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 29, 2015 Share Posted June 29, 2015 http://www.manualslib.com/download/879202/Radio-Shack-Trs-80-Model-4.html Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 http://www.manualslib.com/download/879202/Radio-Shack-Trs-80-Model-4.html thanks! was looking for that one.. i'll try find the buffers ICs Quote Link to comment Share on other sites More sharing options...
daafies Posted June 29, 2015 Author Share Posted June 29, 2015 thanks! was looking for that one.. i'll try find the buffers ICs oh the drive controller. yea i reseated those yesterday.. Quote Link to comment Share on other sites More sharing options...
JamesD Posted June 29, 2015 Share Posted June 29, 2015 (edited) Try reseating U55, U56, U71, U69, and U70*edit*And the CPU Edited June 29, 2015 by JamesD Quote Link to comment Share on other sites More sharing options...
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