PT-31 - won't power on.. Where to start?

[Chas]

On 12/4/2022 at 11:47 PM, CYBERYOGI =CO=Windler said:

472 means 47 with 2x 0 = 4.7k (4.7 kOhm aka 4700 ohm).

 

I doubt that it fell off by getting mauled by screwdriver. That would make rather the rotary part crack off but the bottom stays in place. I suspect the pins to be corroded off by battery acid, which makes it likely that also other components got damaged.

 

 

Cheers for reminding me how to read the trim pot rating! It came back now you pointed out how the 472 number is broken down.

 

With my PT80, the trim pot almost certainly was damaged by physical force. Look at the picture below and you can see where two legs were snapped off, and also the scratches on the board from where someone likely poked a screwdriver/ long object through the tuning hole of the case. Thankfully, no sign of any battery acid leakage on the board. Luckily with a replacement trim pot and also a replacement transistor in the rhythm circuit (I was getting permanent white noise when the drums were engaged), all has worked fine ever since.

 

 

  

 

[CYBERYOGI =CO=Windler]

Is also the PCB part of the trimmer broken in halves? Then for sure it was an idiot with more muscles than brain. When a dirty or corroded trimmer does not respond, of course people may try force, but in most misused trimmer only the rotating metal part gets mangled such that it losses contact to the carbon track or falls off when the rivet comes loose.

[534N]

I should have the little trim pot piece in a couple days or so and I'm about to start my vacation time finally. But.. I'm not sure if I got the wrong value potentiometer. I ordered 2k because I saw "2.2KB" printed on the board in that part's place, but I never learned what the "B" in "KB" is for.. I can't find an answer on the internet. Does anyone know? Is it possible the PT80 uses a different value for the resistance of its tuning trim pot or do I need to order and wait again? I don't want to go through the trouble of soldering this thing in to find out it's the wrong part and it won't function correctly but I don't know where to get a solid answer on this since no one seems to have clear pictures of the inside of a PT-30 or 31 or the service manual. I get the idea that it's better to have a pot with higher resistance than one with lower resistance if the exact measurement can't be found. I don't see anywhere to get the 2.2k rated pot, but I did find a 4.7k, which is strange because all the other options are rounded to the nearest hundredth or thousandth place (ex: 1k, 5k, 10k, 100k, etc.)

 

Thanks in advance if anyone has an answer for this. It would save me some time.

 

I'm not sure if this is a lost cause. Originally, I wanted to earn the pride of fixing it myself, but lately, I just want to hand it over to someone else and pay a bit of money to fix it or find out if it's even possible to fix it, because I have no idea what's wrong with it.. but I have no idea who to take it to. I imagine vintage toy keyboard repair people are pretty rare, and in Thailand no less, it's even more of a challenge with the language. I know electronics are quite similar across many different types of devices so maybe it's possible to find someone.. but I feel like I'm going to get weird looks taking a dinky little toy thing into a computer repair specialist. What do you guys think?

 

For now, I am going to wait for a confident answer on the potentiometer (even though that probably won't fix the fact that it doesn't power on at all) and work on a side project. I'm going to add an output jack to another keyboard (my Yamaha PSS-100) and start planning out the isolated output mods on my MT-68. I have already fallen in love with my new MT-65, so the 68 is definitely becoming the lab rat. I'll make a separate post about that soon if anyone wants to follow along and help with my newbie questions. 

Edited December 12, 2022 by 534N

[CYBERYOGI =CO=Windler]

B means logarithmic, i.e. the value does not change linear along the turning range of the potentiometer. Using A would make pitch vary faster at one end and slower at the other, which makes it harder to adjust.

 

https://en.wikipedia.org/wiki/Potentiometer

 

Installing a 2.2k trimmer very likely will make sound, but may be an octave too high or at least you loose half of the lower tuning range. A 5k would be close enough to replace 4.7k. A much higher (e.g. 50k) pot would make the tuning range too sensitive to small motions (awkward) but likely permitting to tune several octaves lower.

 

 

Edited December 13, 2022 by CYBERYOGI =CO=Windler

[534N]

@CYBERYOGI =CO=Windler - Thank you so much for clarifying the meaning of the "B" that is printed on the board! That makes a lot of sense to me now.

Ok, so we know for sure that it's 4.7k for the PT-30/31 models? It's definitely the same as the PT-80, which is what we got pictures of? That's where we got the whole 4.7k idea from originally. I assume a lot of the parts are the same. I just want to be 100% certain before I put the time in to installing either of the parts and find out it's wrong.

 

I saw a PT-30 for sale today on FB Marketplace but it had a broken screen. It sold shortly after I looked at it. I'm not sure if I should be kicking myself for not buying it.. but it was a little beat up, and the seller wanted $20 for it. I already sunk $9 into my broken PT-31 (which I had falsely been told had a working screen and powered on) so if I sink another $20, I'm basically at $30 for no guarantee. It's not a lot of money really.. but I don't know if I would be capable of transplanting the screen from the PT-31 with that delicately thin ribbon cable, or if the PT-31's screen is even still functional as a separate part. Argh.. I guess the waiting game continues.

 

Honestly, if I find a working PT-30 and the case is not perfect, I will consider transplanting everything into the PT-31 case because I really love the way it looks. Is that a really absurd idea? Haha. What am I doing with my life.. T_T

Edited December 13, 2022 by 534N

[ctt956]

Thanks @pianokeyjoe! Good luck getting the second one fully functional! Mine also seems to have the constant white noise @Chas mentioned, though it's all the time and not just during drums. It sounds similar to tape hiss. Is it detrimental to leave it like this?

Edited December 13, 2022 by ctt956

[pianokeyjoe]

1 hour ago, ctt956 said:

Thanks @pianokeyjoe! Good luck getting the second one fully functional! Mine also seems to have the constant white noise @Chas mentioned, though it's all the time and not just during drums. It sounds similar to tape hiss. Is it detrimental to leave it like this?

Hmm.. Well iif the board is working, and making sounds normally I do not see any harm in the hiss but without an audio/video example I can not really be certain. Mind you my current failures with both my units.. The fully dead one has that HISS while the other that works part way, does not have a hiss perse but rather a faint hiss if you put your ear to the speaker like we all used to do when kids lol!

[Chas]

10 hours ago, ctt956 said:

Thanks @pianokeyjoe! Good luck getting the second one fully functional! Mine also seems to have the constant white noise @Chas mentioned, though it's all the time and not just during drums. It sounds similar to tape hiss. Is it detrimental to leave it like this?

 

@ctt956 - My memory was playing tricks on me as I forgot that the white noise didn't only appear when using the drums, it was always there (in the accompaniment section) and got worse when triggering the drums. I posted a video of this issue on my old YouTube channel that showed this, and if you look in the comments you can see that I located the problem to a faulty transistor. Hope this helps!

 

 

 

Edited December 14, 2022 by Chas

[pianokeyjoe]

NOPE! That white noise is LOUD LOL! Yeh I have never had that issue on a Casio not even my broken ones. I have had that issue on a ROLAND JV1010 Synth module I bought in 2001 though. It would hiss real loud suddenly and randomly. Also a Behringer FX3202 mixer with built in Effects. I got rid of both units fast!  @Chasfound the issue, I would say it makes sense a transistor would be out. I always would have thought it was a defective main IC chip so I just got rid of the things to get my money back.

[CYBERYOGI =CO=Windler]

AFAIK the white noise is generated by CPU pins 22 & 23 (mixed through 2 resistors?) and routed through a transistor as VCA for snare/hihat envelopes. Likely the electrolytic capacitor that controls the decay time is dead and so holds noise at 100%. Of course also conductive battery leak residues may cause it to stay on.

 

The chance of transplanting the LCD from a PT-31 is similarly high like a successful brain transplant including patching all nerves of the spinal cord. Once these foil cables are torn/removed, there is no chance to reattach them. You may try to hold it in place with adhesive film and press it on with a window insulation foam tape strip, but AFAIK the chance that it will be fully functional is perhaps 0.1%.

Edited December 15, 2022 by CYBERYOGI =CO=Windler

[534N]

An update for anyone who is interested:

 

Some of my bandmates recommended a Thai guy who fixes electronics locally and they had some good results. I messaged him and dropped off the keyboard. I get the idea that he doesn't specialize in more complicated electronics, but I have no idea. He has repaired all kinds of appliances and guitar amp stuff. Now I'm just waiting for an update.

 

Let's see if I get lucky.. Maybe it will be a cheap, quick fix that I couldn't identify myself. Or maybe he will tell me that this thing is hopeless and he can't help me. I gave him the little 2k trim pots I bought and I mentioned that I'm not sure if it's the correct part. I'm not sure he knows either.

 

Pray for my poor little junker Casio. I really like this thing for some reason, so I'm hoping it can be brought back to life haha..

[ctt956]

Thanks for the responses @pianokeyjoe and @Chas! I think I will just leave it as is for now. @534N best of luck with your PT-31!

[534N]

@ctt956- Thank you.

 

Unfortunately, the electronics repair guy said he couldn't fix it. He said it was beyond his ability. So... I may not have any choice but to give up on it for now. If it's beyond his ability, it's unquestionably beyond my ability as well. Bummer..

 

Hopefully I will get lucky and come across a PT-30 or another PT-31 eventually. They don't seem to show up very often and I think buying it off eBay is way too expensive these days (especially after shipping and import taxes)

Anyway, thank you all for the responses. I'll keep this thing around and hopefully figure out the problem someday.

[pianokeyjoe]

Sad to hear it my friend. I know my PT20s have hope but I am more in a tight situation of home remodeling that keeps me from having the time and proper space and setup to fix the boards properly, more so than simply not being able to fix them. I can fix them, I just know it will require more tools and more light.. good golly miss molly, more LIGHT lol! And space. Keep your MT400V and PT31 safe and return to them when you are better able and can have ore time and tools to do the job right or until you get replacements. Asia may have more of those things around than the USA since they CAME from Asia originally. Have you seen the Japan electronics district videos on youtube?? Holy Molding! I want to visit JAPAN lol!

[CYBERYOGI =CO=Windler]

Need more light? Get a headlamp (possibly with magnifying glasses). Unfortunately most portable LED lamps are too blue, so they seem much brighter to young eyes but do the opposite to seniors, those only get more dazzled because blue scatters much stronger inside the eyeball than other colours. Modding it with warmwhite LEDs (e.g. desoldered from fairylights or LED lightbulbs) may improve that.

Edited December 18, 2022 by CYBERYOGI =CO=Windler