Members gilwe Posted March 28, 2007 Author Members Share Posted March 28, 2007 Cheers ! Something strange is happening. Some of the voices which are not playing in single mode, DO play when I use the Double mode and pick up a preset for Upper section which uses Unision ON. Does it make sense that some component related with the assigner section has gone bad ? Any other idea ? Is the AD7541 related in any way to the assigner circuit ? I wonder if the little crack (which disconncts leg #1 from the metal layer on the top of the IC) has anything to do with that problem I think I'll make an order for one just in case. Link to comment Share on other sites More sharing options...
Members sneakthief Posted March 29, 2007 Members Share Posted March 29, 2007 gilwe - just out of curiosity, did you try wes' voice-swapping suggestion? if so, what were the results? this is an exciting thread! i love gear resurrection posts, especially ones with schematics and tantalums Link to comment Share on other sites More sharing options...
Members Roald Posted March 29, 2007 Members Share Posted March 29, 2007 hey, thumbs up for getting the Obie to work, Gilwe! wish I was capable of such a thing! Looking forward to mp3s once it's done Link to comment Share on other sites More sharing options...
Members gilwe Posted March 29, 2007 Author Members Share Posted March 29, 2007 Thanks guys, I will get into checking the voice/assignment functionaliy soon, and report. Link to comment Share on other sites More sharing options...
Members flattop Posted March 29, 2007 Members Share Posted March 29, 2007 The pin 1 of the DAC is directly connected to the negative side of the TLO81 op-amp (pin 2). I haven't looked up what pin 1 actually is, so I can't really guess to what it's function actually is. I would suspect you would notice some unexpected things happening when turning the various pots. Pin 1 of the DAC is indirectly connected to the D7 line which does help drive the gate circuit. Could you post a pic of the damage to the DAC? Regardless, I would follow USW's advice and purchase one. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members urbanscallywag Posted March 29, 2007 Members Share Posted March 29, 2007 Pin 1 is an output from the DAC. Seems rather important. Link to comment Share on other sites More sharing options...
Members flattop Posted March 29, 2007 Members Share Posted March 29, 2007 Thus the reason why I wonder if there isn't more amiss with the front panel functionality. If all the pot functionality is in order, then I doubt if pin 1 would be contributing to gating issues. I hadn't taken an in-depth look at the circuit, just a quick glance. I didn't know if they were inverting the output etc... I'm been buried in a troubling P5 repair that I finally sorted out. Customer also had me install a curly maple cabinet. Nevertheless, the DAC should be replaced so gilwe doesn't second guess its performance when and if other performance issues arise. Wes Taggart Analogics http://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted March 29, 2007 Author Members Share Posted March 29, 2007 A closer look at the AD7541 - oh yah, it is defected. At least it looks like it is... The trace which is probably originally connected to leg #1, also should probably go to somewhere inside the IC (??) I already contacted vintageplanet.nl as for ordering a NOS AD7541, no answer from them yet (are they responsive in general ?... hmmm) I wonder what would happen if I soldered the upper trace to leg #1, or - could I just use a pencil to draw a line ?... I heard that could work... or is there any conductive glue I can use ?... just wondering... Thanks for checking into it Wes !! As far as it seems control panel / pots work just fine ! (taking out minor contact problems of course). I would replace it in any case... still wondering if that has anything to do with the odd assignment issue... Gee... that P5 looks niiiiccceeee Link to comment Share on other sites More sharing options...
Members urbanscallywag Posted April 1, 2007 Members Share Posted April 1, 2007 what wood is that Wes ? it looks awesome..It says in his post. I am contemplating buying his endcaps made of the same wood for my MS10. Link to comment Share on other sites More sharing options...
Members gilwe Posted April 1, 2007 Author Members Share Posted April 1, 2007 Hey, after struggling with 3 stubborn screws I finally managed to remove all voice boards and mother boards. It look like some contacts are partially corroded. No response from vintageplanet yet though.... I'm not sure about the AD7541, it looks like it is responsible for the scaling (??) Link to comment Share on other sites More sharing options...
Members OPEN OCEAN Posted April 1, 2007 Members Share Posted April 1, 2007 OBX IS SUPER SO JUST GO FOR IT... Link to comment Share on other sites More sharing options...
Members flattop Posted April 2, 2007 Members Share Posted April 2, 2007 The DAC is responsible for taking the digital info (simple version - whether from the front panel or memory) and allowing it to be converted into analog signals that the voice circuitry can use. I would clean off the post connectors as best as you can and try again. Next would be to replace the connectors on the voiceboards and replate/replace the post connectors. Curly Maple. I find that customers really seem to like the non-traditional look and the contrast between the black of the front panel/keys with the light colored wood. It is a striking combination. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted April 8, 2007 Author Members Share Posted April 8, 2007 More News - After taking apart all voice boards, cleaning all voice cards/voice boards contacts, I finally realized what is (probably) going on. The problem is that the system won't "see" voices 4,5 and 6. What I mean is, whenever you set the DIP so it should "see" voices 4,5 and 6 (among all the others), and click the "AutoTune" button, you can notice that the autotune system passes over the 4th, 5th and 6th voices, as if you were to set the DIP so it should ignore 4, 5 and 6... For example - I set the DIP so all 8 voices should be used. Clicking on Autotune, it starts scanning:1 , 2 , 3 ,7, 8 (passing 4,5 and 6) I know it has nothing to do with how many voice cards are in the unit when doing this, as the Autotune system recognizes missing voice cards and telling you that by blinkning the voice indicator where the voice card is missing. I cleaned the contacts of the 4 connectors and sockets connecting the two panel boards, and replaced the 74LS42 which is connected directly with the DIP switch to no avail (I thought that it might be defected, making switches for 4,5,6 act like as if they where set to "open" => not used). What could be the reasons for this behaviour ??..... Falttop, anywhere else to check into ??.... Currently, I actually have a 5 note polyphonic (working) OBXa, using voices 1,2,3,7,8 .... Thanks a lot ! Link to comment Share on other sites More sharing options...
Members mate_stubb Posted April 8, 2007 Members Share Posted April 8, 2007 Maybe the contacts on the DIP switch itself are bad or corroded or dirty. Link to comment Share on other sites More sharing options...
Members gilwe Posted April 8, 2007 Author Members Share Posted April 8, 2007 It looks clean and I already used some contact spray to clean it. Diodes in the DIP circuit appear to be ok as well... I'll check this out again, anyhow. Link to comment Share on other sites More sharing options...
Members flattop Posted April 9, 2007 Members Share Posted April 9, 2007 Looks isn't good enough. I'd replace the dip switch. The dip are so infrequently used that they can and will become non-functional. People think that something lasts longer when not used. Many times it is the exact opposite. Current goes through the switch and when it is not used in 25 years, carbon can build up and create an insulating effect. Sort of what makes a pot scratchy. Whenever troubleshooting, I determine that my mechanical/physical stuff is in order before I pursue any electronic stuff unless it is plainly obvious what is wrong. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted April 9, 2007 Author Members Share Posted April 9, 2007 That makes sense... After messing with the DIP again, I got voice number 5 recognized now as well. I more and more tend to assume it IS the DIP switch (will replace). Cluster, has yours exhibited the same sympthoms and problem ? I got 6 voices working at this point. Some of the voice cards seem to need calibration (at one voice card the scaling is bad...) Thanks so much for your help ! Link to comment Share on other sites More sharing options...
Members Qwave Posted April 9, 2007 Members Share Posted April 9, 2007 Why not use some cables to bypass the DIP switch and to check if all the voice cards are then found by the system ? Link to comment Share on other sites More sharing options...
Members gilwe Posted April 9, 2007 Author Members Share Posted April 9, 2007 All 8 voices are recognized now - I played with the DIP, some contact fluid and switching on an off rapidly - and they are all available again ! So basically I think we're done with the voice recognition system Two different problems arise with the voices - On one card the scaling is bad: frequency gap between each note is smaller than usual - i.e the lowest C is higher than all other voices and the highest C is lower... I wonder which trimmer is the one to control the scaling (going to the schematics...) Also, no matter which sound card is used at position 7, after the machine warms up, voice 7 will always sound distorted and out of tune.... I wonder if this has anything to do with the AD7541. I switched the CEM3360's which are placed both on the upper and lower voice motherboards, thinking the upper one (controlling 5,6,7,8) would be defected, but now change... but I tend to think that one of the resistors going between voice position #7 and the CEM3360 is bad (R6,R7,R8,R9,R10) For now, I just don't use the 7th position as I only have 7 voice cards in hand anyway, but I'd rather fix voice #7 for a heathier system Also, I wonder whether replacing the electrolytic caps on all voice cards (and on the lower/upper control/cpu boards as well) with cheap taiwanese caps, would effect the sound in any way... I'm not touching any non-electrolytic cap ! Thanks all ! Link to comment Share on other sites More sharing options...
Members flattop Posted April 9, 2007 Members Share Posted April 9, 2007 One of the failings of the OB-X/OB-Xa is the voicecard idea. On one hand, it was a good way to provide a customer a way to upgrade. On the other, it provides numerous connections that can go dodgey on you. If any card you put in this position exhibits the symptoms, then it is either a dmux issue or a connection issue. It you review my previous post, always deal with physical/mechanical stuff first. I would press around the connectors while the card is mounted to see if you get a change in response, but that is me. This is a somewhat dangerous option in that you don't want to create a situation where you lose connection to one side of the power supply. I would not suspect the DAC unless the CV to the oscillators was unstable. I would check this at the opamp that provides this cv, not the DAC. Wes TaggartAnalogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members sneakthief Posted April 10, 2007 Members Share Posted April 10, 2007 re. voice scaling: are you using the service manual? see page 10: http://www.lazyblueoctopus.com/OB-Xa_Service_Manual_1st_Ed.pdf the voice scaling on your "bad" voice is adjusted using two different pots. the first pot on the obxa (VPO aka Volt per Octave) is the main one that you need to adjust for the lower frequencies. as with most sawtooth core VCO's, the scaling pot will only get you so far, at which point you need to trim the HI-TRACKing pot in order to compensate for the sawtooth drooping on the hi-freq's. in other words, it gives the vco an extra kick in the ass so it can hit the highs. re. ad7541 - i checked out the schematics for you: http://www.lazyblueoctopus.com/OB-Xa_Schematics_1st_Ed.pdf this is the main d/a convertor for the whole digital control system of the board. basically, whenever the cpu is controlling a voice card, it uses this chip to convert the digital settings to the analog equivalent. it's output is multiplexed, which lets it control various functions in a round-robin style. if this wasn't functioning at all, you wouldn't be able to recall any patches that are stored digitally. as such, it's highly unlikely that the bad tuning and distortion on voice 7 is due to the problems with this chip. you say pin 1 of this chip might be broken - pin 1 and pin 2 are the main analog outputs from this dac. pin 2 is the main signal which goes to the non-inverting input of a tl081 opamp and pin 1 goes into the inverting input. the opamp is wired in a non-inverting configuration (http://en.wikipedia.org/wiki/Opamp) and so pin 1 should be technically going to ground. in other words, it's quite possible the if pin 1 is broken that it can still function... sort of Replacing it is obviously a good idea. Link to comment Share on other sites More sharing options...
Members sneakthief Posted April 10, 2007 Members Share Posted April 10, 2007 but I tend to think that one of the resistors going between voice position #7 and the CEM3360 is bad (R6,R7,R8,R9,R10) does yours have a 10k trimmer also in addition to those resistors? this might also be messed up, although it doesn't quite account for the out-of-tune business.... hmmm. (see page 10 of these schematics http://www.lazyblueoctopus.com/OB-Xa_Schematics_1st_Ed.pdf ) Link to comment Share on other sites More sharing options...
Members gilwe Posted April 10, 2007 Author Members Share Posted April 10, 2007 Hey, Thanks Sneak ! I'll check out the scaling issue... I also noticed that when NOT using the Autotune function, the voice cards placed at the bottom voice motherboard are tuned a bit higher than all those which are place on the upper one.... For example, whenever voices 1,2,3,4 play 440Hz, voices 5,6,7,8 play 420Hz ... (clicking on autotune still set them all to the same frequency) Are there different trimpots for contorlling the tune of the lower and upper voice boards ? Link to comment Share on other sites More sharing options...
Members flattop Posted April 10, 2007 Members Share Posted April 10, 2007 Hey, Thanks Sneak !I'll check out the scaling issue... I also noticed that when NOT using the Autotune function, the voice cards placed at the bottom voice motherboard are tuned a bit higher than all those which are place on the upper one....For example, whenever voices 1,2,3,4 play 440Hz, voices 5,6,7,8 play 420Hz ... (clicking on autotune still set them all to the same frequency) Are there different trimpots for contorlling the tune of the lower and upper voice boards ? This, again, is indicates a possible connection issue. The power supply to each voicecard motherboard is most likely not equal. The auto tune seems to bring them back in line, but this should be checked. Clean and reseat the power supply connectors. Wes TaggartAnallogicshttp://www.analogics.org/ Link to comment Share on other sites More sharing options...
Members gilwe Posted April 10, 2007 Author Members Share Posted April 10, 2007 You're the man ! Link to comment Share on other sites More sharing options...
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