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IC1 Seems Dead

Deck Repair M90

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#1 billaron

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Posted 21 April 2015 - 08:16 AM

Hello guys,

any idea if IC1 (VUC002-001)  can still be found?

Its outputs don't change state while the relevant inputs do. Has anyone else faced the same problem?



#2 toshik

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Posted 21 April 2015 - 08:39 AM

Hm



#3 Superduper

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Posted 21 April 2015 - 10:24 AM

I have seen very few bad examples of IC1.  It seems to be a pretty robust IC.  There is 1 case where the owner seemed convinced that the IC was bad but because I did not personally check do the testing, I can not confirm this to be the case.  This deck has lots of failsafes.  However, with all electronic components, it's nevertheless possible for it to go bad. 

 

If it is indeed bad, then that is bad news because IC1 is not available from any source.  It is obsolete and as it was used exclusively in the M90 and no other models that I'm aware of, there is no alternatives either since it isn't worthwhile for anybody to manufacture them beyond keeping the M90's alive (and once again, this IC does not fail often).  Therefore, the used market is the only source but getting someone to part out an M90 is not easy.  However.  Member Mike here has recently replaced his deck with one he found off eBay.  I'm sure his original deck could be salvaged but his tech wanted to do the swap route rather than the fix route.  If his deck is still available, it might be worth taking a look at.  Search for the archives and you'll find his thread where maybe you can PM him.

 

As for the IC itself, remember that the inputs need to be pulled low to trigger.  Also did you do voltage checks to ensure that the IC is getting power?  If it is not, it obviously will not work and you should investigate the respective power regulator for that 5V rail.  Although the fusible resistors protect the regulators, just because they aren't blown doesn't mean either that transistor or zener or the resistor has not gone bad, which is expecially true if one of the resistors had been replaced in the past with non-fusibles since the fusible resistors are a bit hard to find nowadays.  Also, you should not presume it is getting ground either.  If you tested for voltage with the black meter probe at a ground other than the one the IC sees, the meter may show 5V but if the IC itself does not see ground, then it likewise has no power.



#4 billaron

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Posted 21 April 2015 - 12:39 PM

I have to admit that you can never be 100% sure on electronics unless you check every detail. In my case I am still checking. 5Volts are indeed present on the IC, all inputs have been pulled down to ground (one by one) while watching the voltage of the relevant output pin and I see no change in any of them. This is something that worries me since a faulty IC very rarely has  the same response in every output. 

What worries me also, is that when i pull down the Rew input, the solenoid energizes.But this happens only once. I have to power off and on again and re-pull down Rew input to see it happening.

FR704 seems that has been replaced in the past by a simple resistor 4R7 but other than a sign of overheat on the resistor i have no other findings.(It was the first thing I looked)

Let me show you what readings i take on IC1 :

 

Pin 1 --> Low (0V)

Pins 2,3,4,5,6,7 --> High (5V)

Pins 8,9 Shorted to GND (0V)

Pins 10,11 --> High

Pins 12,13,14,15,16 --> Low

Pin 17 --> 0.016 V

Pin 18 --> 5 V

 

I would have stopped trying to repair it before even disassembling it (it's not mine), but I was really impressed by the design which i find very interesting indeed.



#5 Superduper

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Posted 21 April 2015 - 03:22 PM

When you say the solenoid energizes, is this momentarily or is it persistent?  It is normal for the solenoid to energize momentarily upon any mode change.  Obviously, if you chose RW and tried pressing it again, it is not a mode change unless you are going from RW to FF or Play.

 

In any event, the readings for IC1 do seem proper and it appears only RW illicits a response.  So I would say that it does sound like IC1 is highly suspect.

 

Question...  how are you reading the outputs?  Are you using a meter or are you using a scope?  I wonder if there might be a response that is momentary that won't register on a meter but obvously can be seen on the scope.

 

If I were you, and you feel it's important to get the deck functions restored, I would contact Mike and see if he still has the old deck, and whether he will sell it (or the board) to you.  He is here in USA so it's probably much cheaper to send only the board and not the entire deck.



#6 billaron

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Posted 22 April 2015 - 09:22 AM

Hello again,

I have sent Mike a PM to see if that board is available.I have also informed the owner that this repair may not be doable after all (Gaining some time strategy).

To answer your question Norm, I will use a scope, but I doubt there is any transition on the outputs (except the Solenoid output upon 1st time pulling down of the Rew input), since my VOM's readings are very stable even on the third decimal point.

I will also try to pull up Rew output to see if the motor does anything.



#7 Superduper

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Posted 22 April 2015 - 05:33 PM

I was just wondering if the IC maybe responded with only a momentary high that isn't visible on the meter.  There is a lag on virtually every digital meter that may not register if it was for but a fraction of a second.  The exception might be my fluke 289 in graphing mode but I suppose it doesn't really matter since I'm guessing the output functions woutd require a persistent high rather than a momentary pulse.



#8 billaron

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Posted 23 April 2015 - 02:02 PM

Watching at the basic timing diagram I am wondering about TM input Signal. It Seems to be coming from that photo coupler board . I will definitely have to use the scope and see if that photodiode gets a momentary falling surge on its cathode upon Rew event. I am still not convinced it is the IC lol.



#9 Superduper

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Posted 23 April 2015 - 05:27 PM

I'm not anyplace where I can check the manual and my M90's are all boxed. But I think maybe the deck functions won't work if the door is deemed open. For example, when eject is depressed with deck running, the deck immediately shuts down and retracts the head. So it knows this. Maybe something to look into?



#10 billaron

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Posted 25 April 2015 - 02:30 PM

I think the cassette switch senses the presence of a cassette and that the door is closed. This switch is checked and seems OK. In the meantime when no cassette is present, Stop Input goes to Low as it should. I cant see any other sensor that inhibits deck's operation. I am still concerned about TM input. The manual states that it should normally be at High Level whereas the basic timing chart shows that it is at Low State before any event has occurred.



#11 Michiel

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Posted 25 April 2015 - 03:05 PM

That photodiode does fail. In my case it was shorted, so I had low signal on the timer, when it shouldn't.

Edit: It was the PN202S that failed. Just found the receipt for the replacement part.