Casio HT-700 "forgets" my sounds!

[patrickvf1976]

This might be a long shot and I dunno if anyone in here actually cares much about this synth. Well I got this Casio HT700 keyboard synth and I personally find it very nice, not great, not bad either. However the problem is this: It keeps forgetting my sounds. I looked around online and learned that it would keep sounds in it's memory with batteries in or hooked to the AC adapter. I put batteries in AND I have it plugged into an outlet, but it just won't keep my sounds. And I made some really nice sounds on that thing and it's a pain in the a## to re-program that thing over again. Can someone help me find out what's wrong? Is there a internal battery that I need to switch out? Is the memory kaputt? Someone please help! I really don't want to have to give it away again for I like it for it's sound. Anyone? Please?

[DES]

You would need to find out if there is an internal battery. If so, then it probably needs replacing. The fact that you put batteries in and it still looses user memory seems to point to an internal battery .... But it could be bad memory chips. Have you tried contacting Casio? They might be abe to tell you if there is an internal battery.

You could also try opening it up and peaking inside. You might be able to see if there is one - would probably be the size of a quarter...

[patrickvf1976]

I think the memory itself should be fine because it does hold the sound data, but because it loses it after 3-4 minutes despite batteries and all I've concluded that it has to be a internal battery of sorts. I called Casio and wait for what they dig up from the archives. I rather find out that way before I take that thing apart.

In the meantime - any suggestions for some easy to do mods? I know the moog slayer kind of mods, but what about instructions for audio input through vcf and chorus, and routing the LFO to other destinations (such as VCF or/and VCA)? Is it actually possible to directly access parameters or even re-program the processor? Just some ideas floating around in my head.

[DES]

If your not a tech then it might be betterto wait and see what Casio has to say. Of course if you are thinking of doing mods yourself...wouldn't hurt to open it up and take a look around....might see the fix right in front.

Regarding mods...I have no idea what is out there for that keyboard. Best bet would be Google, Yahoo, Dogpile and other search engines as well as Casio forums and perhaps Youtube..

[patrickvf1976]

Ok, I haven't heard back from Casio yet (surprise.. ), so I opened it up and took a good look at the circuit boards (the main ones). I took me some research to identify the Ram, which seems not to be internally battery backed. I know ther ram isn't shot, because I can store sounds and rhythms, etc in it and it actually remains for a few minutes after switching off. So I assume that there might be a faulty connection between power/battery and ram? I noticed that yes, there was some battery leakage, but it doesn't look like it did any great damage. The amp board looks a little funky though, especially at the end where the cable band bridges it to the cpu board, and since the battery/power goes through that first, I'm guessing yeah, corroded/disconnected trace/pad somewhere, if nothing else? Any suggestions on how to find/fix the problem?

[holy man]

Hi . I have the same problem.somebody told me to check the board for any death soldering but I didn't find any thing.Do you have an idia?did you find the problerm? please also check the zener diode (HZS4bll) in the amplifire board I checked it mine pass two way but I think it should pass one way like all diods!!!

[patrickvf1976]

hmm.. if I remember correctly, a zener diode is designed to let current pass through after a certain threshold is reached, e. g. a 12V Zener passes current at 12V and above. I didn't get around to do much investigating, but I am suspecting that there might be a broke connection somewhere. I'll have to break out my voltmeter and test continuation between contacts.

[holy man]

ok lets do it together to solve our problem cause I really like this funny keyboard.. Is that zener 12v ? I also think about the MB3771 ic because it's a voltage monitor ic beetwen 2 power supply !!

[patrickvf1976]

That was just used as an example. I don't know what the rating of this particular Zener is, but that's basically how they work.

[holy man]

I think it's3 .4 or 3.6 volts!!

[holy man]

Hi my friend I solve my problem!!!! I change the zener and also the c3112 transistor and it works !! . now i can save my settings!!!I appreciate.Please let me know if you fix yours. I think it has the same problem..Good luck

[patrickvf1976]

Interesting. How did you find out that these particular components were the culprits? What was your method to find the flaw? I'm not too experienced with more extensive ccircuits and to be honest tracing needle thin traces in a maze of traces just to find contact points between them gave me some headache. Plus I don't have any schematics for this keyboard. Did you use standard components to replace the faulty ones? I only have 12v and 5v Zeners and standard PNP/NPN transistors. Would these work?

PS: which Zener did you replace? There are plenty of diodes all over the boards.

[holy man]

Hi that's fine. I use 5v zener from an old tv circut and C945 transistor. I think you can use any NPN transistor.Do it man and it works!! There is just one zener beside the C3112 transistor and have a black line

[patrickvf1976]

hmm.. could it be that it was a regular diode after all, and it just simply burnt out, preventing current from passing through? I'm gonna try the diode first. Maybe it's the only problem.

[patrickvf1976]

nevermind.. I looked it up. I believe the diode is part of the amp circuit and has nothing to do with the memory not getting juice. I could be wrong though, but if it solved the problem for you then I guess it's part of the problem. According to the description, it's there to keep the noise level at bay. The tranny seems to me more likely the cause tho. I guess I'll find out soon enough.

[patrickvf1976]

Ok, I tried the transistor, but it doesn't work at all. The memory doesn't hold anything at all now. It used to hold settings for a few minutes, but now it's completely shot! Now what? I'm gonna try the diode tomorrow... hope that seals the deal..

[patrickvf1976]

Hey, it's working now! It was the diode indeed, exactly the same issue as in your synth. I don't think that replacing the transistor didn't make a difference, or maybe it did. I don't care, it works again and that's all that matters now! Thanks for your help man! Now I can continue with my quest for world domination jk... I have some ideas for some mods on this synth e.g. I intend to physically deactivate the chorus and use the chorus parameters to route the LFO to VCF, VCA and use the chorus just as a plain effect, and I might need help figuring it out. Do you actually have a service manual or schematics for the synth?

[holy man]

hi.I don't have the manual just wet your finger and touch some of resistors around the cpu and some ic's while auto style is playing and you can see the effects on drum and bass then you can add a potentiometer (volume) for each to change the bass and drums sounds!

[justinrobert]

Hey, I just got one of these that is suffering with the same problem. Would one of you mind posting a pic of the diode that needs to be replaced? Any tips on where to get the correct one would be great too! Thank you!

[justinrobert]

I just wanted to post a followup to this for anyone else who's having the same issue. I just replced the zener diode in mine and it fixes the issue. I've also taken some pictures to help you locate the correct diode.

1. Open up the HT, there's a ton of screws on the bottom, but they're easy to get out. Once you have the unit open, you'll see a whole ton of stuff, I've provided a picture of the correct board you'll need to look for.



You need to take out all the screws holding in the two main boards so you can access the other side.

2. Remove the bad diode, you need to be decent at soldering. It's not a terribly difficult job though. I had to cut one of the zip ties on the edge of the board to allow me to prop up the PCBs enough to locate the part. Here's a pic of the exact diode that causes the problem.




3. Replace diode. I used a radioshack Zener Diode part no. IN4733A. 5.1v Zener Diode. It's slightly bigger, but works fine. MAKE SURE YOU PUT THE DIODE IN THE CORRCECT WAY!!!! On the radio shack diode there will be a black band on the cathode end. Printed directly on the HT-700 circuit board there will be a zener diode symbol indicating which side the cathode should go. Zener diode's symbol is a triangle with a sorta S shaped line on the end. The cathode side has the line.

4. clip ends of diode and place PCB back inside the HT. Its a good idea to assemble the unit without the screws first and test it to make sure it's all working before you screw the whole thing back together. Once tested, reassemble and you should have a patch saving HT-700. (NOTE!) you MUST have the D batteries installed for the patches to save if you ever unplug power. There is also a mod for this keyboard to add a lithium internal battery eliminating the need for the Ds, this is my next project. That mod, along with some other really cool mods for the HT are located here http://synthstuff.wordpress.com/2012/01/04/casio-ht-700-mods/

[patrickvf1976]

Thanks, great job on explaining it to everyone in such a detailed way. Sorry I didn't get back at you with the cure, I forgot about this post and moved on to issues with some of my other gear. Glad this thread helped you fix the problem. I haven't tried any mods on this keyboard yet, but I was playing with the idea of simplifying the process of quickly accessing a few frequent parameters. See, I found out that the dial is nothing but a simple potentiometer, which triggers parameter/value changes based on current thresholds. I guess I could use my multimeter and figure out the threshold currents for common parameters and put together a simple logic circuit that switches right into that parameter, and maybe an automatic, normally open switch connected to the mode button, which only connects to the logic circuit if the synth is in edit mode.

[justinrobert]

Hey Patric, yeah thanks for getting this tread going and Holyman for discovering the problem. As far as mods, definitely check the link I posted above. There are some great one of adding pots to the filters, adding a real battery backup, and more. Plus he provides full notes and schematics, which is what I used to locate the parts you guys were talking about for this fix too.

Thanks so much to all of you! I'm actually recording with this little guy right now!

[patrickvf1976]

You are welcome! I have a quick question - is it possible at all to ditch the accompaniment and make the sounds playable across the keyboard (basically make it bitimbral) with the parameters of both voices affect each other (cross modulation/filtering) or would you say that's not possible?

2nd quick question: I want to control the chorus depth, frequency, etc. using pots and a switch to turn it on/off from panel (essentially turn it into a dedicated effect), and use it's parameters to set LFO destinations (just upper or both upper and lower LFOs), e. g. 0=default, 1 cross modulates lower LFO with upper LFO, 2=same as 1 but on VCF (disconnected from VCO), 3=upper LFO > DCO, lower LFO > VCA (or VCF, dunno yet)

My problem is where in the circuit does the processor set the parameters for the chorus, so that I can cut those connections and use that to patch the LFO(s) the way I intend to from the interface?

I know I ask a lot but maybe you know enough about the circuitry to give me some hints and suggestions?

[justinrobert]

Those all sound like really good mods and possible they could be done, judging by what rolandsh1000 was able to do with his mods. He wiped out the accompaniment to let the bass have access to the second vcf. However, He would be a much better person to ask about your ideas than me though. I Really know little about mods, just okay at following instructions, haha. I sent him a message about his battery backup mod, but haven't heard back from him yet, but if I do, maybe I can see if he'll be so kind as to jump into this thread. There really seems to be quite a bit that can be done with this little gem of a synth though for sure.

[patrickvf1976]

Hmmm.. I wonder if I could replace the Casio's filter chips with Curtis or SSM chips.. mmmmm chips..