Messages From yamahablackboxes

 


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#1636 Feb 22, 2014

Hi DB,Ok, for starters, you seem to have the service manual, but I'll link to it here for those who want to follow ---Links-Are-Forbidden--- assertion that (on block diagram, p4) that the "Mixing Switch Latch" which then drives the demultiplexing on the other end of the PCM54 might be crap is totally reasonable.A dodgy analog multiplexer chip CD4051 may also be the case. They are so trivially cheap that if I had it opened up, I'd socket and change IC32 or IC33.

The Flip Flop pair of IC63 and IC64 could be possibly dodgy, too.If I had it open, the first thing would be to let it warm up for 5 minutes, check all the power supply rails. My recollection is that it's switchmode parts are somewhat open, so, please be careful.

As per the PDF above, page 15 onwards, have you conducted the self test modes to observe the outputs there.

Do you have access to an oscilloscope, or just a multimeter?

I have a Tx802, which is sadly at someone else's house at the moment, so I can't do a direct recording into my decent (MAudio) sound card. The only recording I have of my Tx802 online is ---Links-Are-Forbidden--- and I cannot remember if it's been passed through a reverb or not - I'm 95% sure it wasn't. So it's not really too much help. (It's a deliberate attempt at creating stereotypical crappy new age music.)

All the best; and I'll be happy to keep working on this with you

/Edward!



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#1637 Feb 22, 2014

I will also assume you don't have the fortune of living in Melbourne, Australia.

I have 2 scopes :P

Hi DB,Ok, for starters, you seem to have the service manual, but I'll link to it here for those who want to follow ---Links-Are-Forbidden--- assertion that (on block diagram, p4) that the "Mixing Switch Latch" which then drives the demultiplexing on the other end of the PCM54 might be crap is totally reasonable.A dodgy analog multiplexer chip CD4051 may also be the case. They are so trivially cheap that if I had it opened up, I'd socket and change IC32 or IC33.The Flip Flop pair of IC63 and IC64 could be possibly dodgy, too.If I had it open, the first thing would be to let it warm up for 5 minutes, check all the power supply rails. My recollection is that it's switchmode parts are somewhat open, so, please be careful.As per the PDF above, page 15 onwards, have you conducted the self test modes to observe the outputs there.

Do you have access to an oscilloscope, or just a multimeter?

I have a Tx802, which is sadly at someone else's house at the moment, so I can't do a direct recording into my decent (MAudio) sound card. The only recording I have of my Tx802 online is ---Links-Are-Forbidden--- and I cannot remember if it's been passed through a reverb or not - I'm 95% sure it wasn't. So it's not really too much help. (It's a deliberate attempt at creating stereotypical crappy new age music.)All the best; and I'll be happy to keep working on this with you

/Edward!







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#1638 Feb 22, 2014

Hi Edward,

Thanks for your quick and great reply! ...and for your great group here and your many generous contributions of service manuals, schematics, and so on :)

>Your assertion that (on block diagram, p4) that the "Mixing Switch Latch" which then drives the demultiplexing on the other end of the PCM54 might be crap is totally reasonable.

Cool. But then wouldn...t that just mean some channels would fail to be output to the Mixed Outputs? To my electronically untrained mind :D, that seems more logical than them being output but plus a lot of white noise.

I guess I could explain noise if it only happened when one or more notes were playing ... as that could indicate improper transitions/bleed between the multiplexed channels ... but the fact that it happens when the OPSII and DAC are supposed to be silent is what confuses me.

Maybe I should order a new PCM54HP just to be safe ... if there...s any possible reason it could be generating white noise when the OPSII is silent? I did rework all the input pins just in case any LSbits were cold-soldered, but it made no difference, as did not replacing the nearby two pairs of capacitors and single resistor to 5 V.

>A dodgy analog multiplexer chip CD4051 may also be the case. They are so trivially cheap that if I had it opened up, I'd socket and change IC32 or IC33.>The Flip Flop pair of IC63 and IC64 could be possibly dodgy, too.

It...s certainly worth trying since, as you say, the parts should be cheap enough that there...s no reason not to give it a go.

>If I had it open, the first thing would be to let it warm up for 5 minutes, check all the power supply rails. My recollection is that it's switchmode parts are somewhat open, so, please be careful.

This is definitely a really good idea before beginning to replace components in the PSU, possibly unnecessarily. I can get a friend who has a voltmeter to help me check this, hopefully soon.

>As per the PDF above, page 15 onwards, have you conducted the self test modes to observe the outputs there.

Not yet, although I might as well have a try later! I do notice that it states a maximal noise level of ...80 dB for the Mixed Outputs, so I wonder where my synth will be when compared to that. I seem to recall some other synth of mine having noise around that level in the past and it not being much of a problem to my ears ... BUT I think that was around 80 dB /after/ it was normalised, whereas the TX802 is quoted at that for a raw signal. I did one recording of a single note of piano last night (now lost) and then normalised it, and if I remember rightly, the noise was around ...65 dB or higher when compared to the full-scale synthesis, and it was very noticeable and annoying, just as it is when playing a single 16-note voice as a performance (and still, but less, annoying as I turn down the polyphony)

>I have a Tx802, which is sadly at someone else's house at the moment, so I can't do a direct recording into my decent (MAudio) sound card.

If you and anyone else ever got a chance to check their TX802 and maybe take a recording, that would be much appreciated! It would help us all to figure out whether this is a normal thing or something weird about my particular TX802. If it is normal, then maybe we can work on a way to improve everyone...s TX802, not just mine!

>The only recording I have of my Tx802 online is ---Links-Are-Forbidden--- and I cannot remember if it's been passed through a reverb or not - I'm 95% sure it wasn't. So it's not really too much help. (It's a deliberate attempt at creating stereotypical crappy new age music.)

Haha, it...s not that bad! :P When it gets quieter near the middle, there is some noise audible, although I can...t really determine whether it...s as bad as mine or not. Thanks anyway!

> All the best; and I'll be happy to keep working on this with you

Thanks so much; I really appreciate all your help! (although it will have to remain virtual as I...m nowhere near Oz, haha)

Cheers,Daniel







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#1639 Feb 22, 2014

Buy a multimeter. You can get a damn good one for $20 these days (back in my day..... he says, at age 36), or an OK one for $10.Try to look for one that has frequency measurement on it if you can. Feel free to email me links to any you consider getting for opinions. Also; list member Fran (Francis Bordeau) is a much more experienced service technicial than I am, and he might have some ideas, too.

Then you follow the schematic and see if the appropriate chips are getting the right voltage to their positive and negative rails. The good news is with almost all digital logic chips (74xx 40xx series chips) it's the top right to the bottom left, and you should be getting 5v on them.

Go to a copy shop, photocopy/print out the schematic, nice and big, a few copies. As you go through and check the voltage of each one, strike out the chip with a highlighter or something similar. I've used that method before, and it works well, and it's kind of relaxing after a while.

Where about in the world are you located?

Thanks so much; I really appreciate all your help! (although it will have to remain virtual as Im nowhere near Oz, haha)

Cheers,Daniel



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#1640 Feb 23, 2014

Bad news:You had probably bad luck and got TX802 from the series with well known hardware bug.Good news:It can be repaired, there's a specialized service center in Vienna, Austria: ---Links-Are-Forbidden--- need to send whole instrument, which can be if not impossible then at least expensive. Despite Alex from this firm is nice person, I doubt he will reveal secret how to repair... Try to ask him.Of course recapping of PSU (or whole instrument) can hardly make things worse.My TX802 is OK.Daniel Forro



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#1641 Feb 23, 2014

for reference, copying my reply from YamahaDX:

Hi Daniel,

Ifound that page before but did not think it was relevant to mysituation as the symptoms sound very different to me: the page makes nomention of hiss/white noise, and compared to the page, I get neitherdistorted voices nor any benefit from turning down the output levelparameter on the TX802's tone generator.

But I appreciate you trying to help.

Yes,a re-cap is something worth trying, as well as replacing digital logicchips, such as the multiplexer and analog out switches, as Loscha onYamahaBlackBoxes suggested to me. I have ordered those two things andalso new versions of the transistors that join the 15 V rails to themain board.

Appreciate any and all other ideas that might explain the specific symptoms I get.

Thanks!







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#1648 Feb 23, 2014

The PCM54HP could be bad but first I would look for a dropped bit on the digital input lines. I had this happen to a 24 bit DAC in a Roland JV-1010. I also had an op-amp just downstream of the DAC fail in a DX7 but that was unbearable distortion. The clue there was the output offset 6 VDC voltage was missing.

Thanks so much; I really appreciate all your help! (although it will have to remain virtual as I...m nowhere near Oz, haha)

Cheers,Daniel



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#1650 Mar 5 10:31 PM

---In yamahablackboxes@yahoogroups.com, narfman96@...> wrote :| The PCM54HP could be bad but first I would look for a dropped bit on the digital input lines. I had this happen to a 24 bit DAC in a Roland JV-1010. I also had an op-amp just downstream of the DAC fail in a DX7 but that was unbearable distortion. The clue there was the output offset 6 VDC voltage was missing.

Yean, and I found a good post of yours from the past that related that story from a Kawai I think, but I already mentioned that I tried reworking the joints on the PCM54HP, to no avail (and I don...t see any broken traces on the way, etc.). The OPSII looks fine, but anyway, I didn...t want to put a soldering iron anywhere near that! Mostly since it...s more expensive and proprietary than the PCM54HP, although a quick trip to eBay revealed only one person selling the latter, and at ..52... not something I can rush to buy without proof it...s needed. :S

I ordered 2068-type opamps to replace the 4558s (LPFs, gain) and 2072s to replace the 072s (voltage followers/buffers), although the latter will take a while to arrive as I had to order from HK due to the much higher costs in Europe. My plan is to replace these two in an individual channel or two and determine whether they grant a significant reduction in noise, in which case, I might replace all of these two types of opamp throughout the whole circuit. I assume no significant sonic signature will be lost as most of that will be due to the OPSII.

Of course, it might be something else afoot, if replacing the opamps makes no difference. But I'm reasonably confident that it's fairly plausible that somewhat noisy opamps like the 072 and 4558, which would be bearable in single or double configs, would get irritatingly hissy when you gang 8 * 3 individual outputs 2 * mixed outputs in mono mode = 26 in a row.

In that case it would be that all TX802s are quite noisy, which some videos I have watched do support, and it is just that not many people notice or complain (at least in a public setting); I have found a few other people who acknowledge the noise on their units, but sadly no stories from anyone who tried fixing it. Luckily I tend to be both perceptive and stubborn. ;)

Anyway, thanks for the suggestion, and I...ll appreciate any other ideas you or others have, whether they...re new suggestions or just comments on my ideas so far






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