Leaderboard

Well this is another one I picked up yesterday, conversation from exchanges unlimited i believe,, had a count up on the rear lamp mask some bulbs holders are not used but it seems to add up the to the exchanges unlimited,, ?? Does anyone remember this machine ?

So the real VFD came in to the workshop as dead, and it was. These devices are quite pricey and I did warn the owner it might not be repairable. However trusty soldering iron in one hand and meter in the other I dived in casting caution to the wind. It has 3 electrolytic caps, 2 x SMD and one through hole. Both SMD caps were effectively open circuit but all three were changed to 105° types. Once these were done and the device powered up the screen was still blank so I needed to drive it with something. Looking up the spec sheet it showed that the SIN/TO pin, if grounded, would switch to test mode and by jove it did, displaying the whole character set. Sending it back for testing expecting a glowing report proved a bit premature. The device was still dead and the machine would only boot up without the VFD connected?? When it arrived again at the workshop I swear it was poking it's tongue out at me. Anyway not to be outdone it was time for a bit more researching. Next to no info on the web, no diagrams or fault repairs on Youtube. So first step was to find out why it was stopping the board from booting. This VFD connects to the 14 way DIL connector via the little PSU board. The only wire which goes directly from the VFD to the board is the BUSY link. I assume this is used to slow the main board logic when it needs to print lots of text to the screen. When this connection was removed everything burst into life! Checking with a meter showed it to be permanently HIGH. Here's a pic of the board so you can see what I was dealing with... Did the BUSY line go direct to one of the LSI chips because if it did that was goodnight Vienna! Trying to trace tracks on this was no easy task either but the BUSY line did appear on the O/P of IC2. This was a single OR gate and the output was stuck high. Checking the I/P showed a nice waveform but nothing on the O/P. I managed to find some replacements on Ebay at a reasonable price and slipped in a new one and bingo, nice waveform on the O/P and with the BUSY link re-connected everything burst into life. You have to take precautions when reworking these boards due to the proximity of other components and plastic parts. Best thing for this is Kapton tape to shield the bits you don't want melted.

Hi all, I think I mentioned these devices a few weeks back so I thought I'd purchase a few and have a play. If you're not aware these devices can emulate ROMs and come in all the sizes and will do masked ROMs too although I haven't got there yet. Amazing so far and so many things I haven't tried yet. They are about a tenner each but the time and effort they save it's a no brainer. The devices can be flash programmed in seconds so no waiting 20-30 mins to erase ROMs and re-burning when you're testing patches to code. Then plugging them in to test and finding they don't work! (yep we've all been there) Once installed in the ROM socket they can be re-programmed in situ via USB. Here's a pic using an MPU3 card... Also big and smaller brothers. They do devices for larger chips but I don't need them as yet. Another advantage of these is you can save multiple images which can be selected by the jumpers so changing code can be done in seconds. Of course in the case of MPU3 & 4 you can't put them in the case as it's not deep enough but that's fine just for testing purposes. Another advantage is you can put the whole image on one device and patch the CS lines to the empty sockets (not tried this as yet) but it's all explained in the blurb. I needed to use these due to trying to defeat the CHR and CRC check as burning traditional ROMs was taking all day. It can now be done in seconds. I'd like to thank John Parker for his assistance with this and taking the time to explain it. Cheers John you are a squire and a gentleman sir. For the guys out there that like hacking ROMs for changing the gameplay, I think these devices will be a godsend. It does also mention in the blurb you can change bytes on a running system, not tried that either but it's all terrific stuff.