This probably apply to a lot of logic problems with various Philips tape decks.
I have a problem that my DCC 600 detects tapes shorter than C60 as stopped way before due. Maybe only 10min in it autoreverses or stop depending on direction.
I have the service manual. It describes reflectors under the spool wheels.
I'm guessing there is IR send/receive on a cb just under this reflector.
Is this a known fault in Philips decks?
How do I fix it?
I have a problem that my DCC 600 detects tapes shorter than C60 as stopped way before due. Maybe only 10min in it autoreverses or stop depending on direction.
I have the service manual. It describes reflectors under the spool wheels.
I'm guessing there is IR send/receive on a cb just under this reflector.
Is this a known fault in Philips decks?
How do I fix it?
I've never worked on a DCC deck but a couple of thoughts...
1/ Rotational sensors would/could be a common problem on any cassette deck. Typically a slotted vane and infrared LED and photo sensor or possibly inductive (a magnetic pickup) and hall effect sensor. Should be easy to rig a dual beam scope (or even a DVM) to each sensor and observe any sudden anomaly.
2/ Make sure the mechanicals are OK and that the reel take up torque and supply spool back tension are OK. Careful observation is needed to see if anything odd happens mechanically when it auto reverses unexpectedly.
3/ Does the DCC format have any form of ID on the cassette used to tell the system control what length tape is inserted. I'm imagining things like slots in the cassette and microswitch detectors like the old CRO2/FE/CR switching on standard decks although its hard to envisage any system like that (if it has it) being the cause of this.
1/ Rotational sensors would/could be a common problem on any cassette deck. Typically a slotted vane and infrared LED and photo sensor or possibly inductive (a magnetic pickup) and hall effect sensor. Should be easy to rig a dual beam scope (or even a DVM) to each sensor and observe any sudden anomaly.
2/ Make sure the mechanicals are OK and that the reel take up torque and supply spool back tension are OK. Careful observation is needed to see if anything odd happens mechanically when it auto reverses unexpectedly.
3/ Does the DCC format have any form of ID on the cassette used to tell the system control what length tape is inserted. I'm imagining things like slots in the cassette and microswitch detectors like the old CRO2/FE/CR switching on standard decks although its hard to envisage any system like that (if it has it) being the cause of this.
Thanks for the tips. I'll look into that.
Funny thing is that the logic works OK on C60 and C90 but not on shorter tapes, like prerecorded.
There is pins for the DCC tape lengths but I'm only playing old analog tapes. They have no length indication.
There is also a quick reverse sensor that reads the reflection of the end tape, but that is only active on DCC. I even tried to solder it off. Nothing happened.
My worst worry is if the logic chip fails. I guess it's the bin if that's the problem.
But I'll have a go at the wheel detection circuits to see if I can determine any irregularities.
Funny thing is that the logic works OK on C60 and C90 but not on shorter tapes, like prerecorded.
There is pins for the DCC tape lengths but I'm only playing old analog tapes. They have no length indication.
There is also a quick reverse sensor that reads the reflection of the end tape, but that is only active on DCC. I even tried to solder it off. Nothing happened.
My worst worry is if the logic chip fails. I guess it's the bin if that's the problem.
But I'll have a go at the wheel detection circuits to see if I can determine any irregularities.
Fortunately the 'big chips' are generally the most reliable parts in a unit and weird faults are usually something external to the chip (such as an incorrect input somewhere).
Look at the reel sensors for starters and also try and determine what conditions cause an auto reverse situation to occur. Prerecorded tapes can be 'tight' from my recollections back in the day. When the fault happens take the tape out and see if the spools in the cassette are free to turn.
Look at the reel sensors for starters and also try and determine what conditions cause an auto reverse situation to occur. Prerecorded tapes can be 'tight' from my recollections back in the day. When the fault happens take the tape out and see if the spools in the cassette are free to turn.
Back from the fumes of various liquids...
Everyting seems to be ok with the motion detectors under the spools. I managed to get both off without destroying the holding tip, and clean the perfect looking IR emitter/reciever under each. I cleaned the perfect looking 6-part reflector under each spool too.
I managed to measure the voltage is going from 0-3volts when the reflectors pass by the IR. I havent got any fancy scope so my measuring in motion is way too slow to really know whats going on, I tried to connect a standard LED parallell to the pins of the IR, but it cannot drive it on any polarity. Not those I had anyway.
Found another tape with a shorter run than C60 and that ran perfectly - so now I'm down to one tape that wont play. It's very loose. I use to slap them in my palm a few times so the tape windings settle in line inside - that always loosen them up.
I measured the problem tape to a couple of others - can't find any differences. Looked so damn hard.
Learned a lot about this machine when disassembling it, but still it is a mystery why it won't plays this one tape - or others maybe, I havent' tried all 200 or so.
Curiosities:
My plan was to get the machine going and rip all tapes through the SPDIF to a computer - yes, it actually converts analog to digital inside - and is better at it than I thought.
I made a test of connecting both the digital and the analog output to the PC simultaneously in a multitracker (Cubase) and monitor both at the same time. Of course a combfilter-effect was heard because of the slight latency between the different outputs.
Well, lets test this...so I found some time compensating plugin where I could adjust delay in milliseconds, and applied that on the early signal, and got it to play exactly in sync with the other. There was also a slight difference in volume, so i found a very precise metering plugin to see what the diffence was and adjusted that.
Now to the fun part: Phase cancelling.
I changed the phase on one of the signals to see if there was any difference in doing A/D in the PC or A/D in the DCC...well, not total silence - but i'm not sure if it's bad or good.
I had to lower the analog >14khz and above by 5dB or so to match the digital signal - but that doesn't tell me if the high end og the analog is overly compensated or the A/D of the DCC is a bit dull. Nomatter what I did I could not exactly phase out everything. There still was som leakage, but really not much. I hade to crank everything up by 60dB to be able to hear it.
Everyting seems to be ok with the motion detectors under the spools. I managed to get both off without destroying the holding tip, and clean the perfect looking IR emitter/reciever under each. I cleaned the perfect looking 6-part reflector under each spool too.
I managed to measure the voltage is going from 0-3volts when the reflectors pass by the IR. I havent got any fancy scope so my measuring in motion is way too slow to really know whats going on, I tried to connect a standard LED parallell to the pins of the IR, but it cannot drive it on any polarity. Not those I had anyway.
Found another tape with a shorter run than C60 and that ran perfectly - so now I'm down to one tape that wont play. It's very loose. I use to slap them in my palm a few times so the tape windings settle in line inside - that always loosen them up.
I measured the problem tape to a couple of others - can't find any differences. Looked so damn hard.
Learned a lot about this machine when disassembling it, but still it is a mystery why it won't plays this one tape - or others maybe, I havent' tried all 200 or so.
Curiosities:
My plan was to get the machine going and rip all tapes through the SPDIF to a computer - yes, it actually converts analog to digital inside - and is better at it than I thought.
I made a test of connecting both the digital and the analog output to the PC simultaneously in a multitracker (Cubase) and monitor both at the same time. Of course a combfilter-effect was heard because of the slight latency between the different outputs.
Well, lets test this...so I found some time compensating plugin where I could adjust delay in milliseconds, and applied that on the early signal, and got it to play exactly in sync with the other. There was also a slight difference in volume, so i found a very precise metering plugin to see what the diffence was and adjusted that.
Now to the fun part: Phase cancelling.
I changed the phase on one of the signals to see if there was any difference in doing A/D in the PC or A/D in the DCC...well, not total silence - but i'm not sure if it's bad or good.
I had to lower the analog >14khz and above by 5dB or so to match the digital signal - but that doesn't tell me if the high end og the analog is overly compensated or the A/D of the DCC is a bit dull. Nomatter what I did I could not exactly phase out everything. There still was som leakage, but really not much. I hade to crank everything up by 60dB to be able to hear it.
Not seeing an LED light when placed in parallel could be normal as the forward volt drop of the IR diodes will be fairly low, and probably lower than a normal visible LED. So ultimately there is just not enough forward voltage for the visible one. Seeing in the voltage on the sensor change from 0 to 3 volts is good enough.
Could the tapes have deteriorated and the problem is simply to much friction on the (what I recall) was a rather large 'multi channel' head ?
Sounds like you are having fun with the rest of it though 🙂
Could the tapes have deteriorated and the problem is simply to much friction on the (what I recall) was a rather large 'multi channel' head ?
Sounds like you are having fun with the rest of it though 🙂
Well, the funny thing is that sometimes it autoreverses after a fraction of a second...it doesn't even have time to let the logic tell if the spools are blocked...I don't get it. Mystery tape...
I'm gonna take out the wheels and put them in another cassette housing. If it still breaks operation it has to be the quality of the tape itself, how strange that even sounds. there could be some safety circuit around the head. Magnetizing sensor or whatnot.
I'm gonna take out the wheels and put them in another cassette housing. If it still breaks operation it has to be the quality of the tape itself, how strange that even sounds. there could be some safety circuit around the head. Magnetizing sensor or whatnot.
Maybe... if it is just an odd tape doing this.
I can't think of any safety circuit other than the usual reel rotation sensors.
I can't think of any safety circuit other than the usual reel rotation sensors.
...so the hunt continues...
I actually took out the spools of the problem tape and put them in a different tape housing. Guess what...it stopped again...my jaw dropped.
First reaction was to rip out the connector of the DCC portion of the tape head to eliminate any possibility of the DCC circuit decoding some noise to give error.
Nope didn't work, tape still stopped.
Now I'm down to one thing: It HAS to be the combination of the exact length of the specific tape making the spools run in a specific speed that the logic chip reads as stopped. Simply bad programming of some sort hitting me after 20 years in the dark ��
One thing that makes me think this is that the head retracts and the makes a small pause before it turns 180. It never does that on any other situation. Bug in a tape deck...there probably is an upgrade for the chip or there wouldn't be any need to be able to see what version the software have...
I could really need a Philips expert right now, so please forward this conversation to one if you know one.
I actually took out the spools of the problem tape and put them in a different tape housing. Guess what...it stopped again...my jaw dropped.
First reaction was to rip out the connector of the DCC portion of the tape head to eliminate any possibility of the DCC circuit decoding some noise to give error.
Nope didn't work, tape still stopped.
Now I'm down to one thing: It HAS to be the combination of the exact length of the specific tape making the spools run in a specific speed that the logic chip reads as stopped. Simply bad programming of some sort hitting me after 20 years in the dark ��
One thing that makes me think this is that the head retracts and the makes a small pause before it turns 180. It never does that on any other situation. Bug in a tape deck...there probably is an upgrade for the chip or there wouldn't be any need to be able to see what version the software have...
I could really need a Philips expert right now, so please forward this conversation to one if you know one.
You might have seen all these.
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I really don't know what to suggest. If there were a firmware/software bug then I would have thought there would be something 'out there' mentioning it.
If it is just an odd tape from many that is the problem then maybe its one of those things that you will never get a definitive answer too.
DCC Anyone? [Archive] - Tapeheads Tape, Audio and Music Forums
DCC 170 confused! [Archive] - Tapeheads Tape, Audio and Music Forums
DCC170 Portable [Archive] - Tapeheads Tape, Audio and Music Forums
DCC heads durability [Archive] - Tapeheads Tape, Audio and Music Forums
I really don't know what to suggest. If there were a firmware/software bug then I would have thought there would be something 'out there' mentioning it.
If it is just an odd tape from many that is the problem then maybe its one of those things that you will never get a definitive answer too.
Both spool wheels need to turn at the approximately same speed. If one stops even a tiny bit (lags), the playback will stop, or the autoreverse will happen. Clean the mechanism to ensure there's no slippage, especially with bad quality tapes that put a lot of demand on a mechanism. This should fix the problem.
Well, at the start or the end of a tape, the spools run very different speeds because the capstan speed is constant and simple physics.
I have many old dusty half broken tapes that run just fine the entire run, and then this (and probably others) tape that break operation after a second or less. It makes no sense at all. If I could simply understand what it is it triggers on, but I can't.
I have many old dusty half broken tapes that run just fine the entire run, and then this (and probably others) tape that break operation after a second or less. It makes no sense at all. If I could simply understand what it is it triggers on, but I can't.
There are indeed a lot of pins poking at the tape. Some are for the presence of any tape, some for DCC, some for rec enable and so forth. None of those seems to make any difference to the specific problem.
I assembled the entire thing yesterday and let it play a bunch of various tapes, and found out that all tapes shorter than C60 have problems staying put. Something is still triggering the 'end of tape' logic, but when I persist to start play over and over again it finally gives up and plays further past the 'problem area' and play to the real end of the tape.
I just donno... It could be unstable due to faulty PSU allthough it looks brand new - no discolourations or buzz whatsoever. As this is uncharted territory for me I need someone to look it up for me. My brother used to fix various hifi, so I'll ask him to look at it.
Otherwise...it's probably back out on ebay to find another deck.
I assembled the entire thing yesterday and let it play a bunch of various tapes, and found out that all tapes shorter than C60 have problems staying put. Something is still triggering the 'end of tape' logic, but when I persist to start play over and over again it finally gives up and plays further past the 'problem area' and play to the real end of the tape.
I just donno... It could be unstable due to faulty PSU allthough it looks brand new - no discolourations or buzz whatsoever. As this is uncharted territory for me I need someone to look it up for me. My brother used to fix various hifi, so I'll ask him to look at it.
Otherwise...it's probably back out on ebay to find another deck.
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