• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Perplexing Sharp RP-117

FrankFIII

FrankFIII

New Member
I have a Sharp RP-117 I've been working on and trying to get fully operational. One of the first things that needed repair was the gear that opens and closes the drawer had split and was loosely spinning on the shaft. A new gear got that part working properly. Next up, the belt that is used to drive the worm gear for the tone arm from the motor was dried out and stiff as a rock. Since it was formed in a pear shape, it would not move when the motor turned. Replacing this belt was actually easier then replacing the platter drive belt.Since it was already open I didn't have to take any additional parts off. I used to pointed and angled picks I use for o-rings and it was done within 5 minutes. At this point I thought I was home free. I put an album in it and it played to the end. I then got adventurous and selected both sides and repeat. IT WORKED GREAT! This is when I discovered the last problem I am working on and would be really grateful if someone has seen this before or had some ideas on what could be wrong.
If an album is playing, if I hit the FWD or REV button to use the APSS system to go to the next song I want to play, the needle is cued then travels all the way inward to the lead-out area, then travels over the entirealbum to the lead-in area and stops the platter. Done.
If I try to use the APMS system where I can individually select songs to play on side A & B or A or B, as soon as I hit the play button after entering my selection, the needle is advanced all the way to the lead-out area. The selection I just made blanks off of the display, then the needle moves all the way out to the lead-in area an stops the platter.
While I can use the TT as is and play an entire album, it would be nice to have these 2 functions working.
I forgot to mention, I do have the service manual and was able to set the signal level for the IR sensor in the tone arm for side A + B to 35 mV as directed.
 
Register to hide this ad
Good job so far.

My first most obvious thought is there a good distinct gap between tracks? Have you tried different records? Perhaps the sensor can't recognize the gaps if they are too narrow or due to certain qualities of reflectivity.

Also, the sensor is only half the track recognition system, is it not? Is there an LED and is it still working well?
 
Montycat said:
Good job so far.

My first most obvious thought is there a good distinct gap between tracks? Have you tried different records? Perhaps the sensor can't recognize the gaps if they are too narrow or due to certain qualities of reflectivity.

Also, the sensor is only half the track recognition system, is it not? Is there an LED and is it still working well?
Click to expand...

Thanks,Montycat. The last thing I tried was a different album. Steve Winwood was getting tired anyway. I'll try yet one more in the morning. I don't know if the sensor is only half the track recognition system, but when I use the APSS system to select, the play selections, the platter is stationary and not rotating. This mode appears to work primarily scanning for the smooth (silent) surfaces between songs or at the beginning or end of an album side. If I use the APMS system to forward to the next song or reverse to a previous one, the platter is now rotating and then in addition to the IR detector on the tone arms, I believe this mode takes the audio signal from the cartridge, amplifies it with an op-amp,then sent to a half-wave voltage doubler and on to the microprocessor. I was hoping one or the other would work,but at this point they are both not working.
 
Although I have the Service Manual, it is less forthcoming with the information I think I need. For example, when I am requesting the APSS system to program selections, what inputs is the CPU expecting and what should be expected for outputs from it. I know in this mode, the platter does not spin so that output is not active. Also since not spinning, I would not expect the amplified and rectified audio signal to be passed to the CPU. I do expect the IR detector signal to be received at pins 44 and 45 at the CPU to tell it when it encounters as space as well as the encoder wheel signal for the position of the tone arm at pins 52 and 53 to tell the CPU what location (address/radius) the blank spaces are located. The problem with the design of this TT is that the platter is in place over the PCB while operating. I need to attach wires to the CPU pins I want to monitor with a scope.
 
Yeah, if the track recognition is taken from audio cues rather than visual that's a whole different can of worms. I'll have a look at the SM later.
 
Ok, track recognition is optical, not audio. The audio portion seems to be only related to the muting of the signal at the ends of the disc.

There are 2 phototransistors and 2 LEDs that detect the track gaps. You should focus on those as perhaps they have failed:

upload_2020-3-24_11-40-35.png
 
Could be a fault or it could be the nature of the beast.

A story:

A shop I worked at for a couple of years special ordered an “Auto Reverse” Sansui for a certain, long standing, preferred customer. Not the Sharp in question but had to use similar in technology. I don’t recall such a turntable being sold under any other brand name.

In any case, it too optically sensed gaps between tracks or at least it was supposed to. The person who ordered the Sansui returned it a short time later complaining it would only locate tracks on its own some of the time. We sent it back under warranty but got returned NFF - no fault found.

The explanation was the gap between tracks had to be reflective enough (which I took as wide enough) for the sensor to react to.

Someone else bought the turntable as a “demo”. returning it again for the same reason. That situation repeated twice more before the store owner just took it out of inventory - fate unknown.

My opinion was that an “Auto Reverse” turntable was a clever idea which could not be implemented to operate 100% of the time. Vinyl recordings were too inconsistent in gap width between tracks.

As a sidebar, the fact it did not have a platter
in the conventional sense, made me point out its foibles to any customer expressing interest.
 
Thank you all. I'll hook some leads to the leads I mentioned above and see what I get for signals tonight. If I do need the sensors, what is available for spare parts for this beast?
 
So I did a little checking tonite on the Sharp RP-117. No earth-shattering news, just a few more pieces to the puzzle.I was able to connect 2 leads to pins 44 and 45 of the cpu. These are the pins that are supposed to indicate the blank spots detected by the IR detectors between songs or at the lead in/out on the album. With the wire leads connected to my scope and a DVM, I did not see any activity at the input to the cpu. So I thought, let me try another album. So I hit the eject button and as the drawer was opening, the signal went high to 4.93V for a split second as the outer edge of the album traveled under the ir sensor. As soon as the album moved away from under the sensor it went back low again. So the signal is not stuck low but does go high on occasion. I then took an LED flashlight and shined it on the sensor. I was able to make it go high, but it was very touchy and only reacted at specific angles or location.
So this is where I am at. With the light I can make it switch states, so the sensor is doing something. When I first started working on this unit, I adjusted the APSS sensor adjustment and WAS able to obtain 35 mV at test points TP201.1 (A) and TP201.3(B) when the tonearm was resting over the lead-out area on the platter as directed. Since I was able to achieve this voltage level as directed in the manual, I take it as the input being good and proper at this point. This 35 mV signal then goes through an LA6324 op-amp, then through an IR2339 voltage comparitor. Since I was able to get a high state at the cpu on occasion like when the sensor was running on the edge of the album or over-driven by my LED flashlight, I am thinking the voltage comparitor may be working properly and the problem could be due to the LA6324 op-amp.
Any thoughts on this? What would be the best way to go considering the location of the board and how in order to take measurements I need to attach leads, then put in an album and see what I get.Each time I want to measure something, I need to repeat the process.

Sorry for being long-winded.... but if this works, it could help someone else out.
 
I say again, it's likely the LEDs at fault. Maybe they are not getting enough voltage or have dimmed. Can you get at them to replace with something newer and brighter?
 
The leds and the accompanying detectors are in a custom molded package that fits in a special compartment in the tonearm. There is also a notch in it with a pin for a spring to allow for, as I can best put it, swivelling of the detector assembly to center the stylus with respect to where the detector is looking.
 
I have an update on the Sharp from today. Montycat, I agree with you there is a problem with the optical detection for the blank spots. However, I thought the odds would be lower of having 2 tonearm detectors bad than something else in the circuit. I went and picked up a LA6324 op-amp to replace IC205 since it handles side A and side B. So I replaced the chip today, cleaned up the repair, then put the module back in and connected together enough to play an album. I now have APSS and APMS fully operational on Side A - only. I can program a selection or perform a forward or reverse on side A. Side B is still behaving like both sides were prior to changing the chip. I now feel I could have a bad optical sensor for side B. Before I go there, I have 1 last thing to try. When I was trying to adjust the signal levels for A and B at TP201 pins 1 & 3 for 35mV prior to changing the chip, side A was at about 21 mV prior to adjustment, while B was about 11 mV. I was able to get both sides set to 35mV, but the B adjustment at VR204 was VERY touchy. I would set the level, but as I pulled away it bounce way off. Could I use the same potentiometer cleaner that you use for volume controls on VR204? If I can take care of B this way, with I may be getting closer to completion.
 
Last edited:
BINGO! The readjustment of the optical level potentiometer for Side B did the trick. The APSS and AMMS is operational on both sides now. I have a couple questions I hope some of the more experienced members can help me with. Now I have this unit working properly I want to lube it. What are your recommendations for a good lube to use on this TT and where is a good place to get it? I did not want to lube it while working on getting it working and get the grease all over the place. Since this TT is decades old, I have no idea of its maintenance history, how can I tell if a stylus is worn to the point where it needs to be replaced?
 
It is finally finished! I had a couple more details to take care of, but due to lack of OEM parts, I had to improvise. First, the green light on the display panel was burned out. This uses a bulb that has a diameter of 0.150 inches and a length of 0.75 inches. It is a axial-shaped light bulb and runs on a 10V supply. Since I could not located any of these bulbs, I used a 12V green radial leaded light bulb that has a 20000 hour life. I was initially going to use an LED, but thought the light produced from it would be to narrow and focused to fully illuminate the front panel. While getting to the bulb on the front panel, I discovered the porous rubber membrane that provides a soft cushion to the front panel buttons which returns them to the fully "un-depressed" state, was dried up, shrunken and crumbling apart. I thought I had located a replacement part from Sharp, but I got a message 2 days later after I ordered that stock was depleted. So, while at my workbench, I noticed a piece of window air conditioner filter foam. It is a sheet of very flexible foam, open celled and 0.2 inches thick. I cut out a piece with scissors and reassembled it all. The buttons now fully extend from the front panel and work when depressed.
 
Last edited:
Great hints and observations here should mine ever go kaput. Mine was given to me, free by a friend, that got it free from the wife of a deceased friend. No one wanted it and he was glad to find anyone that did! Belt was goo, needed cleaning etc, but after all that, it is a very fun novelty table. The styli are still available, though mine seemed fine and I doubt I would ever play anything minty in it, as it’s got a pretty high VTF and being platterless, the W&F is audible in ~ the .15% range based on my listening experience. What platter belt did you end up using and have you listened to any solo piano works that would demonstrate the w&f? FWIW, I have yet to find an album (as long as it is black, & not a continuous Live album, ) where it did not accurately locate the songs. It really is GROOVY. There.. I said it.
 
Hello perryinva. I'm glad you got yours working. To tell the truth, during the refurb process I went through, I bought 2 belts. - a 20" and a 21.4". When it was at the point in time to change them, I took the old one off as it was not goo, but was very dry as in the state of almost crumbling. I took the opportunity to measure it for reference, and while I realize it was probably stretched out, it did measure 22.5 inches. Using that 22.5 as a reference, I ended up using the 21.4 inch belt and not the 20 inch one as it would have been way too tight. Overall I am satisfied with the end result, and while not perfect, as you say it is GROOVY. I did play an album over the weekend that was a live album and had one cut on side 2 and it played fine. I have new 2 audio technica stylus for this for when it should ever need it. There is a good demand for them. I was amazed how the brand-new RP-117 I mentioned 2 posts ago sold at the auction. At the time I entered it, the cost was $ 300 US and was AMAZED at the final cost being $ 1125 for it. So hold onto yours. While surfing the web yesterday, I ran across a PDF for a DAK International catalog from IIRC 1984 that featured a Sharp RP-117 in it. The cost in the catalog was $ 183.00.
 
Yes! I just saw that listing and ABSOLUTELY CAN NOT BELIEVE IT!!’ If there weren’t so many bids, I would say it was a phish of some kind. Wow. Insane. I guess I should go ahead and buy the new styli, so I would be less fearful of it chewing up a record at 3 grams VTF! I would definitely buy one to fix up for resale at a good price if it came along. Geez!
 
You must log in or register to reply here.
Back
Top Bottom