repetto74

I used the square one. The flat one was a little bit smaller and maybe forcing on the main cassette drive. I had some reading issues at the beginning but cleaning the head with IPA fixed the problem :-)

Hi Fred, Thank a lot! Yes luckily it was just the 6810 RAM chip which was causing the problem + my mistakes at a certain point where I mixed the connectors but all looks fine now! PS : By the way the cassette deck player 1010 is fixed also. Your new belt is apparently working good

Job is done! Sorry I did really waste my time and yours here . I have checked on the service manual and it appeared in fact that many of the connectors where mixed and connected the other way around!! I have never fixed a 1050 drive this is my first but as you can see the drive now boots good . At least I found the fried RAM on the first board. I will run a diagnostic test now I assume there are maybe some tuning to be done. I will try to load the test from my SIO2SD device and then hook the 1050 drive with the SIO cable Maybe we have another 1050 taken out from the grave :-)

Ok so I have swapped all the main chips one by one and tested (FDC,CPUT,6532,ROM and RAM). I had exactly the same problem for each swap except when I swapped the RAM 6810 and there I had the dead drive mech and no activity light of the first board :-). So this RAM is bad. What I will do is to use the RAM of the second board into the first board and fire it up. In the picture enclosed this is how I found the main connectors hooked up. Someone may have put his hands there before so can I be sure they are correctly hooked? I have a doubt when I see J10 and J11 not sitting close to each other..... By the way thanks for the park sensor supply but I am located in Europe :-(

As you can noticed from the video the R/W head is bumping at the end of the track rail (like some of the 1541 Commodore Disk Drives) but I do no think this is a normal behaviour.

Hi Guys, Got a 1050 DD for a few bucks sold as non working. I received today a 9V AC 2.1 amps PSU and can start my troubleshooting. The power led is coming up but that's all. No motor spinning and no movement of the R/W head mech. The activity light is off also. What I have tested for the moment is the voltage at the 7805 and 7812 which are both fine and read +5V and +12.05V. I picked up also a spare board untested for a cheap price. Swapping the board with the second and I have now the drive mech coming alive, the disk motor spins briefly then the head mech will step forward and then back to the track sensor and stops. Then the activity light turns on with the disk motor spinning, then all off and on again in a repeated pattern. Is this an indication of a fault code? I will keep this board for the moment and try to repair with this one. For the first board I may think one chip is fried and does not send commands to the drive mech but I will see that later. Let's try to make a working drive with what I have :-) Here is a video of the 1050 in action Thanks Rick

Thanks Adam1977 but I finally picked a RockPower PSU :-)

Yes I found the RockPower PSU from a seller in Germany and I am located in Belgium so ordered one for 16 euros :-). This is done.

I am declaring interest also for a 1050 PSU :-). Located in Europe also :-)

Is 2.1 amps sufficient? I read somewhere it would need more around 3 amps to be on the safe side and avoid PSU overheat. EDIT : I have checked other users and there is this RockPower PSU at 2.1 amps which seems to work pretty good so I just ordered one :-). Just to wait a couple of days and I can start some T/S.

Hi guys, I picked up a 1050 DD non working for a few buck and I would try my chance to repair it. -the drive came with no PSU and I know it is difficult to find one but if anyone has a link where I can get one of these 9V AC PSU's. I am located in Europe and need a 220V PSU. -With the hope of putting my hands on a suitable power unit I would like some tips on how to diagnose fault on this drive. Apparently the guy said the red light comes up but that's all, no sound of motor spinning or whatever. It may have a problem with the 12V line of the motor I think but will need a PSU for that. Where should I check for the 12V inputs? The 12V regulator? Also what can i check now is the impedance of the read/write head to ensure it is ok. Does anyone have the resistance values at each pin of the R/W connector for me to check ? The mechs is a TANDON. Many thanks in advance.

Yes the zig zag pattern is only visible with an LCD screen and lifting one log of C54 has completely cleared them :-)

OK I have solved this finally! :-) For info the right hand side of resistor C54 should be lifted up. This will cut the RF box from the video signal so you will loose composite output but the zig-zag patterns are completely gone by doing this. Probably the RF modulator is just making some interferences.

Hi Fox-1 / mnx Sorry for pictures, the problem comes from pictures taken in landscape mode with an Iphone :-) Can't be the S-video cable as it is the same I am using with the modded 600XL and the output is far better.

Hi Guys, This thread is old I know but maybe some of you can guide me through a small issue I have with this mod. All looks fine and I have a crisp and clear picture on a PAL 800XL after performing this mod. The only thing is a checkered pattern I do see on the background which I do not have on another 600XL after having performed a different mod. I am using an S-video cable with an LCD monitor. What can cause this and is there a way to improve the image? PS : The 600XL mod looks totally different, I remember having to cut a couple of traces and solder some resistors in parallel but the result is much better without this zig-zag effect. Many thanks Rick

Hi Ksarul, Thanks for the info. I bought a couple of TIM9904ANL a week ago from the same seller of your link :-). So waiting for them to test. I have a programmer which is the TL866 and do not know if it can test also. I will keep in mind the 74LS362 as a probable replacement also :-) The TIM9904/74LS362 are early versions and need a 48 MHz crystal. The later TIM9904A needs a 12 MHz crystal. So check the markings on the crystal and that will show which version of clock chip you need. The original TIM is marked TIM9904ANL so I assume it is the one for a 12 Mhz crystal. Next time I will crack open the TI99/4A I will give this a look

Hi Ksarul, Thanks for your answer which is confirming what I was thinking :-). I definitely assume that TMS9904 will not work as should the original TIM9904. TIM9904 are hard to find, I hear that there is apparently an alternative 74LS362 which can do the same job. Is that true?

Yes I do have the original still working. I am just buying spare parts whenever I found them just in case :-)

So you mean I may try to piggypack the original clock generator with the new one?

HI Home Automation, Both IC's comes from the same reseller and I barely do not think tahat they mix good and bad IC's. I am somehow convinced that the TMS9904ANL is not the proper clock generator suitable for the TI99/4A.

Hi Guys, I am buying some spare parts of the TI99/4A to have them available for any repair needs. I have found some e-bay resellers in China with VDP chip, Clock generator, CPU and rams. I have tested successfully the VDP chip (does not look as a new old stock but a new manufacturing) but the clock generator fails (black screen and continuous tone on power up). Now I would like to be sure the one I purchase is the correct because the marking is different. The E-bay clock generator is marked TMS9904ANL while the original one is marked TIM9904ANL. Are they different then or is the e-bay clock generator a scam? Thanks, Rick

I have only check colours displayed in the main low res graphic mode. are there some more ? I am not very used to Tandy Coco programming.

hi jhd, yes in basic mode I can display any of the 8 available colours without any problem for both machines and as per the pictures colours are displayed as they should be at the prompt. What is weird is that the LCD screen is not really displaying a B&W pictures as you can see in pictures. It is more like a mix of faded blue and green with a lot of striped patterns. weird ...

Hi guys, I have both a PAL coco1 and a PAL coco2 the first being modded to composite and the second one using the RF output on a CTR monitor. Both will display a decent prompt screen (green and black). Today I received a CasDuino and tried to load some CAS images (Donkey King) but I have a weird result on screen for both. On the COCO 2 hooked to the RF output I do have a clear picture whenever the green and black display mode is shown but a scrambled picture with washed out colours when in High Res mode (pictures) as if the CRT Tv tuner goes out of sink when the high res video signal kicks in. On the COCO I through composite on a PC screen or the CRT TV I do have a stable picture but the colours are completely washed out with only a mix of blue and green on screen (this is barely unwatchable). What can be wrong? Is there any tweak to be done to the color circuitry potentiometer? Thanks

Well difficult to read out this schematic image. Wondering just if the whole project was available to print out the circuit board. I do see also that this is apparently for NTSC COCO's while mine is a PAL version.Thanks anyway! :-)