Messages From yamahablackboxes

 


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#1878 Jun 4, 2015

Hi,I found a thread on here about someone with a TX81z that turned on but had no sound output, in the end they replaced a capacitor but unfortunately they neglected to state which one they replaced to fix the issue. My TX81z has the same exact symptoms, it fails the audio output test on both outputs and the headphones.Please could someone tell me what caps I need to replace to get her up and running again, the power supply seems fine all other tests pass she lights up and receives MIDI fine.Any help appreciated,Thanks,JJ



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#1879 Jun 4, 2015

I'd suppose you have volume set up high... and MIDI channel set to the same one as transmitting device...I don't think it's good idea just to follow what somebody did, your problem may differ.I would start with PSU to check if all voltages are as they should be, if electrolytic caps are OK...For the best diagnosing the problem you need oscilloscope, to check the signal after DAC IC12 step by step to the output.Then I would check muting transistors TR1 and TR2 and mute circuit around TR3 to TR5, maybe the problem is there. Check also1/50 electrolytic caps on the output of IC1.Changing the backup battery is always good with such old machine.Daniel Forro

On Jun 4, 2015, at 9:46 PM, Joe yojoeseph@... [yamahablackboxes] wrote:

Hi,I found a thread on here about someone with a TX81z that turned on but had no sound output, in the end they replaced a capacitor but unfortunately they neglected to state which one they replaced to fix the issue. My TX81z has the same exact symptoms, it fails the audio output test on both outputs and the headphones.Please could someone tell me what caps I need to replace to get her up and running again, the power supply seems fine all other tests pass she lights up and receives MIDI fine.Any help appreciated,Thanks,JJ



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#1881 Jun 6, 2015

I also have a TX81z that has no audio. I diagnosed the problem to the power supply though. If I remember correctly, it provides /- 15 and 5. One of the 15v legs was reading zero.

I checked the archives here and folks said that it's probably a bad voltage regulator or a cracked trace on the PWB. Unfortunately I'm also extremely lazy and haven't cracked it open since that point many years ago.I think the voltage traces are labeled on the PWB so it would be quite easy to check. I also found a schematic somewhere for the power supply which would also help.Good luck and let us know how it works out!







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#1882 Jun 8, 2015

One other thing you can check without opening your TX81z and that is settings effecting scales. It is possible with thoseYamaha FM synthesizers and tone generators that arecapable of supporting micro-tonality and "special" programmable scales is to have settings that cause the frequency ofsome orall of the notes to be outside the range of the instrument (and your ear).I had this happen with a DX7with E! Card after I replaced the battery. It turned out that a combinationof the scale parameters caused all the notes played to be outside the normal range of 20 - 20,000 Hz and therefore out of the range of the audio outputcircuitry.Once I reset the scale parameters back to defaults, I had my output back. No parts required! This is something to consider especially if you haveeither changed the battery or otherwisedone anything that could effect the programming of the scale settings on your TX81z.Otherwise, best of luck...Rawl



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#1883 Jun 18, 2015

I have a tx81z that does the same thing. Your problem is somewhere in the 15v line because that's what powers the audio.For me, one of the windings on my transformer is dead and it happens to be the one that powers just the audio circuit. I can not find a simple replacement for the transformer. Please post back if you happen to find some solution or replacement transformer.Thanks,Chase



One other thing you can check without opening your TX81z and that is settings effecting scales. It is possible with thoseYamaha FM synthesizers and tone generators that arecapable of supporting micro-tonality and "special" programmable scales is to have settings that cause the frequency ofsome orall of the notes to be outside the range of the instrument (and your ear).I had this happen with a DX7with E! Card after I replaced the battery. It turned out that a combinationof the scale parameters caused all the notes played to be outside the normal range of 20 - 20,000 Hz and therefore out of the range of the audio outputcircuitry.Once I reset the scale parameters back to defaults, I had my output back. No parts required! This is something to consider especially if you haveeither changed the battery or otherwisedone anything that could effect the programming of the scale settings on your TX81z.Otherwise, best of luck...Rawl







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#1884 Jun 18, 2015

I realize this may not be the best long term solution and the chassis is 1U, but possibly while searching for a replacement transformer with all of the needed windings, you could possibly use an external PS with a power jack input to the chassis if you just need the 15 volts.Some companies will re-wind transformers for you with the old lamination stack and covers, but expensive, probably cheaper to replace the entire unit.And I realize adding a second transformer in the small chassis would be very difficult. From: "Chase Smith plus_321@... [yamahablackboxes]" yamahablackboxes@yahoogroups.com> To: "yamahablackboxes@yahoogroups.com" yamahablackboxes@yahoogroups.com> Sent: Thursday, June 18, 2015 11:06 AM Subject: Re: [yamahablackboxes] TX81z No audio but other wise working

I have a tx81z that does the same thing. Your problem is somewhere in the 15v line because that's what powers the audio.For me, one of the windings on my transformer is dead and it happens to be the one that powers just the audio circuit. I can not find a simple replacement for the transformer. Please post back if you happen to find some solution or replacement transformer.Thanks,Chase



One other thing you can check without opening your TX81z and that is settings effecting scales. It is possible with thoseYamaha FM synthesizers and tone generators that arecapable of supporting micro-tonality and "special" programmable scales is to have settings that cause the frequency ofsome orall of the notes to be outside the range of the instrument (and your ear).I had this happen with a DX7with E! Card after I replaced the battery. It turned out that a combinationof the scale parameters caused all the notes played to be outside the normal range of 20 - 20,000 Hz and therefore out of the range of the audio outputcircuitry.Once I reset the scale parameters back to defaults, I had my output back. No parts required! This is something to consider especially if you haveeither changed the battery or otherwisedone anything that could effect the programming of the scale settings on your TX81z.Otherwise, best of luck...Rawl







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#1897 Jul 13, 2015

Hi Rawl,

Thanks for the information about scales that is interesting however the TX81z fails the built in output test, would the scales settings cause this? I would have thought Yamaha would make the test immune to something that simple...Thanks,JJ



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#1898 Jul 13, 2015

I don't think this is relevant to your problem, of course the instrument is immune against similar mistakes:First - micro tuning can be used only in the Performance mode, it has no effect in the Single voice mode - I suppose you try to test your instrument in Single mode.Second - even with the extreme settings of micro tuning some sound would always go out.I would recommend to check once more this:- set instrument to the Single mode, Basic MIDI channel = 1, Note On/Off = All, Combine Mode = On, Master Volume = 99, select preset sound A01, connect both audio outputs, connect external MIDI controller to MIDI In, set its transmit channel to 1- play the external controller, check if PLAY LED blinks- set MIDI CC7 (Volume) to max (by the foot pedal connected to controller keyboard, by some controller on controller keyboard, or by data sent from external sequencer or other MIDI controller)- try to send some music data to the instrument from sequencer, try to change receiving channel, or try to set some test performance with 8 sounds on 8 MIDI channelsIf it still doesn't play, then there's is some software (OS) or hardware problem (PSU, sound generating chip YM2414, CPU, ROM, OS EPROM, DAC YM3012 or audio circuits). Then it would need expert diagnostics and repair (if possible)...And have you tried diagnostics test, described in the Service manual (page 28)?Good luck!Daniel Forro

On Jul 13, 2015, at 11:48 AM, yojoeseph@... [yamahablackboxes] wrote:Thanks for the information aboutscales that is interesting however the TX81z fails the built in output test, would the scales settings cause this? I would have thought Yamaha would make the test immune to something that simple







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#1965 Apr 1, 2016

Thanks for this extensive reply Daniel I really appreciate it when people go to this much trouble to explain things thank you.

For the benefit of others who might encounter this issue the problem was solved by replacing one of the smaller capacitors in the power supply unit section.

I upgraded the OS and it's working like a dream!

Yamaha really built these things to last, in order to resolder the capacitor I had to remove the PSU board which is a little fiddly but not to hard, then it was a simple five minute solder job.

I also fixed the power supply unit buzz with a simple piece of cardboard pressing between the transformer and the outer casing. The synth PSU is now completely silent which is good.

I have stuck it back in my right now but if anyone really wants to know what Cap it was just post a reply here and I'll see what I can do to help.

Thanks to all who assisted

JJ


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