4013 flip-flop conundrum (Pioneer PL-L1000 turntable) - Page 1
Forum section: electronics / repair

author: Winters
author_rank: Newbie
timestamp: June 24, 2025, 06:42:49 pm
content: Hello everyone, this is my first post here.I'm a turntable enthusiast and repairman. I mostly deal with European brands and am more into 1960s record changers than state-of-the-art Japanese units.However I'm currently working on a Pioneer PL-L1000 that won't switch to 45 rpm (33 works fine) I can't really wrap my head around the 4013 flip flop that is supposed to do the switching.First things first - switch has been thoroughly cleaned, it has virtually no DC resistance when pressed. All neighbouring capacitors (C23, C24, C25, C26) have been replaced with quality components.I have already replaced the TC4013BP flip-flop with an original Toshiba device.I can't get the output of said IC (Q2, pin #13) to change and I don't really see how it is supposed to work.These are my findings:when the button is pressed, there is a pulse on pin #4 (RESET1). However, given that SET1 and CK1 are always high (connected to the 10V rail) this does not translate to any change on Q1 (pin #1).Only Q1* (pin #2) toggles.By default (turntable powered on) it's at H. Pressing the button causes it to change to L, pressing it again causes it to revert to H.However, Q1* (pin #2) HAS a definite falling edge every time the button is pressed.Q1* is not connected to anything whereas Q1 is strapped to CK2 input of the second flip-flop, which is supposed to act like a T-flip flop.How is the 1st FF supposed to clock the 2nd FF given that Q1 output is always at H? What am I not seeing here? There's not even a smallest pulse on pin #1 (Q1 output) when the switch is pressed. This is confirmed by the truth table in the TC4013BP datasheet:I would greatly appreciate your help and will be more than willing to offer my advice on some units that I'm more familiar with.Best regards and greetings from Poland,Piotr

author: darkspr1te
author_rank: Frequent Contributor
timestamp: June 25, 2025, 07:32:20 am
content: I have attached a link too different manual which show there is extra logic involved not shown on your diagram, page 15 shows the signal from speed sw goes via another chip (look for size S/W selector and trace from there)https://www.manualslib.com/download/793557/Pioneer-Pl-L1000.htmlhope this helpsdarkspr1te

author: golden_labels
author_rank: Super Contributor
timestamp: June 25, 2025, 07:39:01 am
content: Welcome to the forum.The right part clearly becomes nothing more than:If the circuit doesn’t rely on some transient state to generate a short pulse on Q1, I can’t see how it is supposed to work.I’m even more puzzled by your mention of Q1 switching between states. As long as the clock is bound to positive rail, this remains a basic SR latch. There is no room for toggling and it goes against all the truth tables and diagrams I found for this IC. Isn’t the chip simply damaged?Other than above I can offer nothing more than confirming your assessment so far is correct. The actual switching action is done by the second part (one on the right). It’s negated output (¬Q2, pin 12) is fed back to data input (D, pin 9). So on each clock pulse (pin 11) that part flips its outputs. This kind of use is shown in TI’s datasheet(1):(1)Figure 9, page 11.

author: darkspr1te
author_rank: Frequent Contributor
timestamp: June 25, 2025, 07:43:28 am
content: I cant seem to find the diagram OP is using, the diagrams i find are different as are the pins used,see attached picturesI was look at record size switch not speed switch, ignore mei did find a trouble chart for the issue though.darkspr1te

author: Winters
author_rank: Newbie
timestamp: June 25, 2025, 03:37:52 pm
content: Thank you for your replies!Quote from: darkspr1te on June 25, 2025, 07:32:20 amThis is the same service manual I have - the only thing that the two switches have in common is ground - pressing the button shorts the voltage present on the other leg of the switch to ground. Record size selector is working properly.Quote from: golden_labels on June 25, 2025, 07:39:01 amAllow me to clarify: Q1 (pin #1) is not switching between states. It stays at H all the time. Pressing the switch does not cause ANY traceable pulse on pin #1 and this seems correct according to the truth table I attached.However, pressing the switch produces a definite pulse on ¬Q1 (pin #2). It's not toggling (I made a mistake here, sorry about that) but there is a momentary change from H to L every time the switch is pressed.I'm not the first repair guy that is fighting against this problem - the unit arrived to me with a Philips 4013 chip and there was some damage to the traces around this IC. According to the service manual and photos of original unmolested PCBs, the original IC was Toshiba TC4013BP.I fixed the obvious lifted pads and going by the troubleshooting section of the service manual, my first suspect was IC5 (the TC4013BP in question). I replaced it with a new TC4013BP fresh from Mouser.I think I will try to switch pins #1 and #2. Theoretically it should work, given that pin #2 has a pulse when the switch is pressed while pin #1 does not.Best regards,Piotr

author: golden_labels
author_rank: Super Contributor
timestamp: June 25, 2025, 05:40:46 pm
content: Note: I misread the last Winters’ message. Please ignore this postIf there is a short pulse on Q1, then I’d say everything works as intended. That pulse triggers the clock input of the second part. Since that second part is configured to flip state on each clock, each button press causes Q2 and ¬Q2 to be flipped.The designer would rely on undocumented behavior, but they may have a good reason to do so. One is that flipping happens on clock rising edge. If ¬Q1 output was used, the rising edge would not come until the button is released. Whereas this transient spike causes a very short pulse, which gives us the rising edge right after the button press.So, if I understand what is going on correctly, it seems everything is fine.This is my current view (grayed out everything irrelevant):The behavior would go like that:Code:button ---. ,- part 2 triggered | … and then again …v v |----------------------------------------------------------------------RESET1 H ---. ,-----------.L `-------------' `-------------------Q1 H ----. ,-----------------------. ,---------------L `-' `-'CK2 H -----. ,-----------------------. ,--------------= Q1 L `-' `-'Q2 H ,--------------------------.L ---------' `-------------¬Q2 H -----------. ,------------L `-------------------------'DATA H ------------. ,-----------= ¬Q2 L `-------------------------'

author: Winters
author_rank: Newbie
timestamp: June 25, 2025, 08:22:57 pm
content: Quote from: golden_labels on June 25, 2025, 05:40:46 pmThere is no pulse onQ1. Q1 is always at H. Nothing changes there - or my scope is not good enough to catch a potential transient (I have a simple 20MHz Hameg. As most of my work is with turntables, I rarely have anything digital on my bench). Anyway, the second FF is not affected by pressing the switch which seems to confirm my reading.However, as I mentioned earlier, there is a very clear pulse on¬Q1.The hypothesis that this design relies on undocumented behavior which only applies to a certain series of the TC4013BP available at that time (late 1970s) seems to be somewhat plausible. Now, is there any other way to make it work other than using ¬Q1? The speed changing once the button is released is way better than not being able to change it at all, so I will try it anyway.

author: golden_labels
author_rank: Super Contributor
timestamp: June 25, 2025, 08:57:35 pm
content: I did read your last post wrong, it seems. Please disregard what I said.But that also means I’m out of ideas.The second part is clearly configured to flip when its clock input is triggered. So the first part must produce that pulse. But how is it doing it on Q1, I can’t tell. C23 + R18 form a high-pass filter. This alone produces a short pulse, when the button is pressed. So the left part of 4013 isn’t used for that purpose. Using it as a buffer sounds most reasonable, but that doesn’t explain the use of Q1 instead of ¬Q1.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 25, 2025, 09:46:41 pm
content: The circuit cannot workas drawn. Here is the logic diagram from Toshiba for the TC4013BP. It agress with the logic posted by golden_labels. The "set" input overides and forces the Q output high. The "reset" input overides for the not-Q output (which is what you are seeing).Trace-out the path from pin 11. The schematics for these players were probably drawn by hand, i.e. there is every chance that errors have been made (and some corrected) in translating the drawings into actual circuits.

author: golden_labels
author_rank: Super Contributor
timestamp: June 26, 2025, 04:04:00 am
content: Joining the request to trace the actual circuit.To be sure it’s not us 2025 dorks failing to understand 1970s geniuses, I checked over a hundred magazines, application notes, and cookbooks from the era. I certainly missed some instances, but I found this kind of pattern in none of what I spotted. 4013 is used for monostable/one-shot operation, in multiple configurations, but not like that. That also covers similar situations, like 7474 or some bare NAND gates.

author: Winters
author_rank: Newbie
timestamp: June 26, 2025, 09:59:46 am
content: Well, the problem is my drawing ends up exactly the same as the schematic!I made a quick sketch using a photo of the actual, unmolested PCB. The PCB is two-sided (very rare for a turntable) but everything related to IC5 (TC4013BP) is on one side.The only thing that differs from the schematic is that there is a provision for some kind of capacitor that could be connected between pin #1 and ground. There is a capacitor symbol printed in this spot, but it has no number and is not depicted in the schematic diagram. However, neither my PCB nor other units found on the Internet have anything actually installed there.The only thing that comes to my mind is that such cap could be used to filter some potential transient noise. To me it seems like a provision for adapting lower-quality, noisier chips. Am I right?Anyway, here is the photo:And here is the PCB drawing from the service manual. I marked the unknown cap with "?".Best regards,Piotr

author: Andy Watson
author_rank: Super Contributor
timestamp: June 26, 2025, 12:14:52 pm
content: Quote from: Winters on June 26, 2025, 09:59:46 amI have to agree, the PCB does match the schematic! Curious!Also curious, but probably just a coincidence, IC5 is listed as a JC4013BP in the parts list. I wonder if that was significant or just a typo?If it were my deck and my problem to solve, I would sever pin 1 close to the chip body and link the now vacant PCB hole to pin 2.

author: golden_labels
author_rank: Super Contributor
timestamp: June 26, 2025, 01:27:19 pm
content: I digged a gold nugget for you.The 1985 Toshiba’s databookgives a different truth table for their 4013:We are not insane. \o/edit:Bonus,Fairchild in 1975 used an even different truth table in their 4000 series:

author: Winters
author_rank: Newbie
timestamp: June 26, 2025, 02:06:21 pm
content: Quote from: golden_labels on June 26, 2025, 01:27:19 pmBingo! That explains everything.I guess I will have to hack the circuit somehow, anyway. The difficulty is that I have to get a rising edge on pin #1.

author: golden_labels
author_rank: Super Contributor
timestamp: June 26, 2025, 02:42:29 pm
content: If you’re going to desolder the entire part and replace it with a new one, perhaps using a DIP socket with a daughterboard is going to be a better option? No hacks on the PCB needed this way, limits modifications to the “ancient” gear.If you plan to leave this component in place: snip off Q1 leg completely, bridge ¬Q1 to where Q1 was attached on the PCB? The toggling action is going to be delayed, but I assume the high-pass filter (C23+R18) will not let it be a long delay. Though, if the chip is damaged, it’s always a question if you want to still rely on it.Alternatively, if Q1 seems completely dead and non-conducting, perhaps a 4.7 kΩ resistor between Q1 and ¬Q1. Should provide enough current to drive the clock input of the next stage, while preventing excessive current or signals fighting, if Q1 decides to wake up from slumber.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 26, 2025, 02:59:42 pm
content: It appears that this problem also affects Roland Synths:https://electronics.stackexchange.com/questions/277994/how-is-this-cd4013-application-supposed-to-workVery sneaky of Toshiba to change the operation but keep the old part number!

author: Winters
author_rank: Newbie
timestamp: June 26, 2025, 03:33:58 pm
content: Quote from: golden_labels on June 26, 2025, 02:42:29 pmWell, the problem is I don't have the original TC4013BP. The unit arrived to me with a Philips HEC4013 - which has the same logic as the newer 4013s. No wonder it didn't work! I now have a new Toshiba TC4013BP installed.I'll try to switch pins #1 and #2. I'll see how it works. If it doesn't, then I'll have to come up with some kind of adaptor.

author: Winters
author_rank: Newbie
timestamp: July 01, 2025, 08:29:14 am
content: Update and summary:I (or should I say WE) made it work! I snipped pin #1 off and connected pin #2 in it's place with a small piece of wire.It works like a charm. There is no noticeable delay in switching.Many thanks for all your replies!Best regards,Piotr