M90 deck help ! (continually clicking)
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Cheers Norm, replaced belts and indeed it improves it engaging into play.Superduper said:
Now, when I put a cassette in it auto plays without pressing play button, pressing stop sounds like it is going to stop but it auto plays again. Pressing eject does open the door and pressing it a few times makes the deck stop. No other buttons work at all other than stop which kinda works but not properly. So FF/REW and PAUSE have no effect at all.
Look, I'm not sure I'm right since I can only go by symptoms. No way for me to test or confirm any suspicions. All I'm saying is that it sounds like it's behaving like the play circuit is shorted. That means rather than closing the circuit when you depress the button (normal), that circuit may be behaving like it's always connected. I didn't say anything about the resistor which has nothing to do with anything. In fact, there is only 2 real failure modes with resistors and if it was shorted, that circuit would probably still function although it could consume too much current and failure of the IC might be a concern, and if it was open, it wouldn't play at all. However, neither of those failure modes would result in perpetual play so it's a red herring. Now there are some other appurtenant components and their failure might result in unpredictable behaviour, especially if they are tethered to some other line. But the resistor was in series.
My suggestion of a possible shorted switch is because as far as I know, there is no autoplay feature on the M90 except for a start timer which engages play when (1) a cassette is present in chamber, (2) you initially plug the unit in with (3) power switch already engaged, and (4) timer set to play. Other than that, there is no reason the cassette should automatically start when you insert a cassette and close the door.......... unless the button (or circuit) is behaving like it's closed. There are many reasons, the button itself could be shorted, there is also a remote jack, there are also logic gates (IC706, IC707) that ties into the play circuit too. Any of the things mentioned could play a role. YOU do have to do your own test abd measurements. You have the boombox so that's all on you. Nobody here could give you a play by play or step by step on something like that.
So if the play is perpertually engaged, it seems like depressing the stop button might disable play long enough until you let go of stop button, then starts again. Also, the cassette deck has a eject sensor switch that STOPs the deck when eject is depressed. The purpose is to prevent damage to the heads in the event a deck is attempted-ejected while deck is playing. Of course once the cassette is extracted, another sensor prevents keys from responding without a cassette present. All this sounds like the play circuit is constantly energized, correct? That's all I can offer you and you'd need to figure the rest out yourself.
As for the play circuit, it appears that pin 5 is closed to pin 8 through a current limiting resistor to initiate play action. Since pin 8 is 0v (low) that suggests to me that pin 5 is high and purpose is to draw the circuit low to energizes the play function (or any of the other functions). If that's the case, then pin 5 is somehow may be unintendedly being drawn low. You can verify by removing the solder from pin 5 to the pad, to remove it from circuit. If it no longer autoplays, then it's being drawn low. You'll need to determine how that is happening on your own.
My suggestion of a possible shorted switch is because as far as I know, there is no autoplay feature on the M90 except for a start timer which engages play when (1) a cassette is present in chamber, (2) you initially plug the unit in with (3) power switch already engaged, and (4) timer set to play. Other than that, there is no reason the cassette should automatically start when you insert a cassette and close the door.......... unless the button (or circuit) is behaving like it's closed. There are many reasons, the button itself could be shorted, there is also a remote jack, there are also logic gates (IC706, IC707) that ties into the play circuit too. Any of the things mentioned could play a role. YOU do have to do your own test abd measurements. You have the boombox so that's all on you. Nobody here could give you a play by play or step by step on something like that.
So if the play is perpertually engaged, it seems like depressing the stop button might disable play long enough until you let go of stop button, then starts again. Also, the cassette deck has a eject sensor switch that STOPs the deck when eject is depressed. The purpose is to prevent damage to the heads in the event a deck is attempted-ejected while deck is playing. Of course once the cassette is extracted, another sensor prevents keys from responding without a cassette present. All this sounds like the play circuit is constantly energized, correct? That's all I can offer you and you'd need to figure the rest out yourself.
As for the play circuit, it appears that pin 5 is closed to pin 8 through a current limiting resistor to initiate play action. Since pin 8 is 0v (low) that suggests to me that pin 5 is high and purpose is to draw the circuit low to energizes the play function (or any of the other functions). If that's the case, then pin 5 is somehow may be unintendedly being drawn low. You can verify by removing the solder from pin 5 to the pad, to remove it from circuit. If it no longer autoplays, then it's being drawn low. You'll need to determine how that is happening on your own.
BoomboxLover48
Boomus Fidelis
That is correct!Alberto said:WOW!! Thank god we have Norm here.
I really appreciate his patience and attention to detail. My two M70s are fully working because of his interactions here on boomboxery.
BoomboxLover48
Boomus Fidelis
indeed.
Thanks Norm...
The only thing I have found problematic is that Q701 is now:
B: 7.38v
C: 7v
E: 14.35v
From what I see, IC702 should receive 7v VCC since the emitter of Q701 should be 7v.
D701 on the base of Q701 is one I've replaced, testing the transistor in board seems to check out fine, guess I will have to remove it to be sure.
Thanks Norm...
The only thing I have found problematic is that Q701 is now:
B: 7.38v
C: 7v
E: 14.35v
From what I see, IC702 should receive 7v VCC since the emitter of Q701 should be 7v.
D701 on the base of Q701 is one I've replaced, testing the transistor in board seems to check out fine, guess I will have to remove it to be sure.
On the face of it thats what I thought.
The emitter of Q701 connects to ic702 pin 6. Both should be 7v but are 14v.
On board I have folliwed the traces and checked voltage along all parts on the trace and all are 14v.
Looking down at the transistor, the base is on the left, followed by the collector with the emitter on the right.There is also a ceramic cap connected to the base and collector pins.
The emitter of Q701 connects to ic702 pin 6. Both should be 7v but are 14v.
On board I have folliwed the traces and checked voltage along all parts on the trace and all are 14v.
Looking down at the transistor, the base is on the left, followed by the collector with the emitter on the right.There is also a ceramic cap connected to the base and collector pins.
You know, I'm highly suspicious that you've re-installed that transistor backwards or it's the wrong transistor. And if so, that zener diode and fusible resistor (if it was actually replaced with a fusible) is probably about 1/2 way to diode and resistor heaven.
Anyhow good luck on the repair. I'm outta here.
Anyhow good luck on the repair. I'm outta here.
Dave, I'll try one more time to explain and show you what I'm seeing through my eyes.
Synopsis of normal behaviour: Q701 is the gate valve that meters the amount of voltage to IC702 through (E). The controlling device is D701, which sets/tells Q701 how much voltage to give IC702 (the REEL MOTOR driver). Basically D701, being a zener diode blocks voltage and bahaves like a regular diode (1-way valve) until it reaches a preset and calibrated volatage and then an intended avalanche failure occurs and voltage is shunted to ground. The only reason it does not burn up is because it is getting is power through a 1k current limiting resistor (R701). The feed that goes to Q701 is FR701 and protects the circuit. This whole setup I just discussed is a 7.0v voltage regulator. With a 7.5v zener diode, Q701 will regulate voltage to 6.8v to 7.1v or so. That's because every semiconductor has a certain amount of voltage drop. In most cases, .6-.7v.
In short:
FR702 powers the regulator directly from the power rail (highest voltage)
FR702 supplies "protected" power to Collector of Q701
D701 determines regulated voltage, in this case, 7.5v will be provided to (B) of Q701, excess shunted to ground.
Q701 (E) is the "regulated" output and powers IC702 which in turn is the driver for the cassette reel motor.
We know: D702 appears to be working (for the moment) since (B) is reading 7.5 +/- volts.
One thing I can say is that MATH NEVER LIES. So trust the math, distrust everything else. Therefore, when readings don't make sense, you can never blame the math.
Problem. You said that collector voltage is reading 7volts. The collector is tied directly to, and getting full system voltage through FR702. If you feel that is a correct reading, then you must check voltage at both sides of FR702. If you are reading full voltage at unprotected side and 7.0 volts at protected side, then either of (2) things are occurring. a: the resistor has failed and has excess resistance or b: the protected side has a short which is causing enormous voltage drop. Since that resistor is only 4.7 ohms, I will say that it will be a huge short to cause such an enormous voltage drop. If the resistor has not failed, and you don't have a short, then your readings or locations of measurement is wrong, or... if you are reading 7.0 volts at both ends of FR702, then I need to say BS, because D701 also gets power through that rail and it's filtered through a much higher resistance resistor and it's getting MORE voltage at 7.38?V. Well, other possibilities exists to explain that such as poor or failing trace, etc but I'm presuming you are checking all that before asking for help.
Problem #2: You said that the emitter is getting 14.35v. All the power from that circuit is supposedly supplied by the regulator in question. You are saying that you are getting 7.0 input (from a direct connection to system voltage). Yet you are getting 14.35v at the output to a circuit that relies on power from the regulator..... See the problem? 7v in, 14.35v out? Doesn't comport, right? So aside from the first enigma, which you need to account for and which already doesn't compute, you will also need to account for the raised circuit voltage at the output. The only way that happens is if that circuit that is being fed is generating it's own voltage independant of the regulator since it's fer dang sure not getting from the failed regulator (if your readings are right). And that doesn't necessarily mean truly generating,it could be getting it's volage from someplace else. But if you study the diagram, you'll see IC702 really is tethered to the reel motor and ground and some signaling circuitry which operates on low voltage and current (being supplied by other IC's).
Bottom line, something is not right and you need to investigate further to set yourself proper beforehand because when I see a set of readings that does not compute, I distrust (the numbers) or (the method employed to obtain them) or failure of the formula (which presumes and relies on a properly set of installed components). In other words, when I look at a circuit, I presume a certain type of behaviour. If something is not installed properly installed, then the entire behaviour and results will be different. You say Q701 was never out of circuit. That's fine. In fact, I read further back that after you originally replaced the zener, you were getting proper readings at the regulator. Now, you say it's all wacked. Well, something has changed while you were fiddling with it between then and now, right? Also, you need to make sure the boombox settings are correct before measuring. Every circuit diagram has a set of settings and rules before reading voltages, otherwise the readings will change. For example, for 1 schematic, it might prescribe power on AC, AFC set to off, Tuner set to FM, dolby-off, etc. etc.
Now, I'm a generous guy and never can resist a call for help but I do have some flaws and those are that I'm not very patient so I'll never make a good teacher, I say things direct as they are, and I shoot from the hip. I never intend to be rude but my comments can sometimes come across that way, but anyone that knows me personally knows that's not how I am.
So when I told you that the measurements were wrong or that the transistor is installed backwards, or that you are measuring from wrong spot.... what I was attempting to do is express to you in one sentence that something does not make sense but I trust the math and the formula is broken so you'll need to figure out where the mistakes lie or was introduced to break the formula beforehand because think about it for a second; Without the boombox here, I'll need to brainstorm, evaluate the diagram, and take a hour to type this response and explain how the regulator works and why the readings don't make sense. And since nobody here can see a bridged solder joint, an inverted transistor, confirm the pin assignment where measurements were taken, meter settings, etc. all we (and I) can do is make suggestions based on the diagram. I presume you value our time as much as your own and as I'm not very patient, I don't want to waste my time considering things we can't control. Could the readings be right yet there be some other reasons for mismatch? Yes, but none good and most of them introduced such as bridged solder joints, or other issues of operator error. There's simply no way for us to go trough the whole list. You need to exhaust all that beforehand. Just go back above to the first problem reading and study it for awhile. You will see that this one reading alone already is a problem and doesn't make sense and if you trust your own readings, then you'll need to resolve that first.
Synopsis of normal behaviour: Q701 is the gate valve that meters the amount of voltage to IC702 through (E). The controlling device is D701, which sets/tells Q701 how much voltage to give IC702 (the REEL MOTOR driver). Basically D701, being a zener diode blocks voltage and bahaves like a regular diode (1-way valve) until it reaches a preset and calibrated volatage and then an intended avalanche failure occurs and voltage is shunted to ground. The only reason it does not burn up is because it is getting is power through a 1k current limiting resistor (R701). The feed that goes to Q701 is FR701 and protects the circuit. This whole setup I just discussed is a 7.0v voltage regulator. With a 7.5v zener diode, Q701 will regulate voltage to 6.8v to 7.1v or so. That's because every semiconductor has a certain amount of voltage drop. In most cases, .6-.7v.
In short:
FR702 powers the regulator directly from the power rail (highest voltage)
FR702 supplies "protected" power to Collector of Q701
D701 determines regulated voltage, in this case, 7.5v will be provided to (B) of Q701, excess shunted to ground.
Q701 (E) is the "regulated" output and powers IC702 which in turn is the driver for the cassette reel motor.
We know: D702 appears to be working (for the moment) since (B) is reading 7.5 +/- volts.
One thing I can say is that MATH NEVER LIES. So trust the math, distrust everything else. Therefore, when readings don't make sense, you can never blame the math.
Problem. You said that collector voltage is reading 7volts. The collector is tied directly to, and getting full system voltage through FR702. If you feel that is a correct reading, then you must check voltage at both sides of FR702. If you are reading full voltage at unprotected side and 7.0 volts at protected side, then either of (2) things are occurring. a: the resistor has failed and has excess resistance or b: the protected side has a short which is causing enormous voltage drop. Since that resistor is only 4.7 ohms, I will say that it will be a huge short to cause such an enormous voltage drop. If the resistor has not failed, and you don't have a short, then your readings or locations of measurement is wrong, or... if you are reading 7.0 volts at both ends of FR702, then I need to say BS, because D701 also gets power through that rail and it's filtered through a much higher resistance resistor and it's getting MORE voltage at 7.38?V. Well, other possibilities exists to explain that such as poor or failing trace, etc but I'm presuming you are checking all that before asking for help.
Problem #2: You said that the emitter is getting 14.35v. All the power from that circuit is supposedly supplied by the regulator in question. You are saying that you are getting 7.0 input (from a direct connection to system voltage). Yet you are getting 14.35v at the output to a circuit that relies on power from the regulator..... See the problem? 7v in, 14.35v out? Doesn't comport, right? So aside from the first enigma, which you need to account for and which already doesn't compute, you will also need to account for the raised circuit voltage at the output. The only way that happens is if that circuit that is being fed is generating it's own voltage independant of the regulator since it's fer dang sure not getting from the failed regulator (if your readings are right). And that doesn't necessarily mean truly generating,it could be getting it's volage from someplace else. But if you study the diagram, you'll see IC702 really is tethered to the reel motor and ground and some signaling circuitry which operates on low voltage and current (being supplied by other IC's).
Bottom line, something is not right and you need to investigate further to set yourself proper beforehand because when I see a set of readings that does not compute, I distrust (the numbers) or (the method employed to obtain them) or failure of the formula (which presumes and relies on a properly set of installed components). In other words, when I look at a circuit, I presume a certain type of behaviour. If something is not installed properly installed, then the entire behaviour and results will be different. You say Q701 was never out of circuit. That's fine. In fact, I read further back that after you originally replaced the zener, you were getting proper readings at the regulator. Now, you say it's all wacked. Well, something has changed while you were fiddling with it between then and now, right? Also, you need to make sure the boombox settings are correct before measuring. Every circuit diagram has a set of settings and rules before reading voltages, otherwise the readings will change. For example, for 1 schematic, it might prescribe power on AC, AFC set to off, Tuner set to FM, dolby-off, etc. etc.
Now, I'm a generous guy and never can resist a call for help but I do have some flaws and those are that I'm not very patient so I'll never make a good teacher, I say things direct as they are, and I shoot from the hip. I never intend to be rude but my comments can sometimes come across that way, but anyone that knows me personally knows that's not how I am.
So when I told you that the measurements were wrong or that the transistor is installed backwards, or that you are measuring from wrong spot.... what I was attempting to do is express to you in one sentence that something does not make sense but I trust the math and the formula is broken so you'll need to figure out where the mistakes lie or was introduced to break the formula beforehand because think about it for a second; Without the boombox here, I'll need to brainstorm, evaluate the diagram, and take a hour to type this response and explain how the regulator works and why the readings don't make sense. And since nobody here can see a bridged solder joint, an inverted transistor, confirm the pin assignment where measurements were taken, meter settings, etc. all we (and I) can do is make suggestions based on the diagram. I presume you value our time as much as your own and as I'm not very patient, I don't want to waste my time considering things we can't control. Could the readings be right yet there be some other reasons for mismatch? Yes, but none good and most of them introduced such as bridged solder joints, or other issues of operator error. There's simply no way for us to go trough the whole list. You need to exhaust all that beforehand. Just go back above to the first problem reading and study it for awhile. You will see that this one reading alone already is a problem and doesn't make sense and if you trust your own readings, then you'll need to resolve that first.
BoomboxLover48
Boomus Fidelis
Norm, thanks.
D701 and D703 replaced and voltages are now correct so that issue is now resolved.
I'll continue testing for the auto play problem on the play section as you mention above.
Incidentally, using my remote has exact the same effect whereby stop works (then it auto plays immediately) and no other buttons work.
D701 and D703 replaced and voltages are now correct so that issue is now resolved.
I'll continue testing for the auto play problem on the play section as you mention above.
Incidentally, using my remote has exact the same effect whereby stop works (then it auto plays immediately) and no other buttons work.
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