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AN640 IC for Technics DD TT unobtainium

I'd just worry that if a Japanese designed and fabricated IC is dead, then a version from the USSR with the quality their semi products were at, will be a bit weak.
 
What you are describing sounds like loop instability. The stability conditions for PLLs are quite complex, as the large signal and small signal regimes are very different, but ultimately have to do with phase shifts in the error loop. This doesn't sound exactly like a typical IC problem, but rather something to do with the loop time constants. Could there be an electrolytic or tantalum in the circuit that acts as the integrating capacitor? If its value had drifted, or ESR risen, then you might first have marginal stability (in small signal regime, but not large) and now no stability at all.

My (limited) experience with failed ICs is that they usually fail totally, rather than go slightly off.
 
I'd second that, if they fail, it tends to be fatally but you can check each output at the pins.
The caps on each leg are where I'd start to look first. Lot's of 10uF to change! Had similar with a bad joint on a cap causing an output problem.
 
PigletsDad said:
What you are describing sounds like loop instability. The stability conditions for PLLs are quite complex, as the large signal and small signal regimes are very different, but ultimately have to do with phase shifts in the error loop. This doesn't sound exactly like a typical IC problem, but rather something to do with the loop time constants. Could there be an electrolytic or tantalum in the circuit that acts as the integrating capacitor? If its value had drifted, or ESR risen, then you might first have marginal stability (in small signal regime, but not large) and now no stability at all.

My (limited) experience with failed ICs is that they usually fail totally, rather than go slightly off.
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Yes, I have designed (basic) PLL's...
It had occurred to me that it could be something on those lines but freezer spray and heat gun on the IC were bringing it in and out of fault so pretty good indication it's the IC! This is my present theory but read on...
I was thinking more in terms of a missing phase or two from the drive IC and the remaining one/s hugely overcompensating (trying to anyway), hence the motor giving a big jolt of torque, then platter slows before another working phase kicks in and repeats it thus giving a set flutter of a few Hz... call it extreme cogging! It is going on 20 years since I last looked at it and came to this conclusion so I am certainly planning on having another look and going into greater detail before doing anything else:) I didn't have an ESR meter back then for a start!

It is certainly possible that heating/cooling of the IC were skewing its characteristics (higher or lower gain etc) such that it just managed to achieve lock... however, IIRC it is just a motor drive IC and not part of the PLL ie loop filter, phase comparator etc...

It's completely stripped and has all sorts of junk piled on top of the resulting pile of parts at the moment after my cat pissed on it and I frantically stripped and washed it before the "alien blood" like properties of cat piss did any damage! This was about 5 years ago in itself!

I've known several IC's fail in a way that could be temporarily "fixed" with a squirt of freezer spray or the heat gun or have just gone intermittent so no they don't always fail completely....

Whilst looking for a replacement IC on line I did stumble on something about repairing this generation of Technics TT's which use this chip set and one bloke was saying that in his experience it is VERY rare for one of the IC's that make up said chip set to fail and it almost always turns out to be something else... so a bit of hope there:)
 
If it's working with freezing spray, I'd still check the surrounding components first but....
If not, time to get the fuming Nitric on heat and a dropper to selectively decap the IC region gently. Have acetone on hand to neutralise of course. Once the bakelite is off the IC itself, time to get the microscope on it and use your LCD liquid crystal kit to isolate the failure point. If you have a SEM then you can try Active voltage contrast, which of course sounds way better than passive . Once isolated, pop it into the FIB and remove the glass over the failure point and then rebuild the (probably) Aluminium track with platinum from the FIB. Finally, test and if all ok, fully rinse in acetone and put a bit of epoxy on the open wound.

Yeah, just find a donor....
 
Lol, I take it that's your line of work then.

Jez if you do go Usa ask mrdog, his brother is based there, he might drop ship for you. He did our last Us group buy shipping for us.
 
Used to be! Now i try to make money...

In chips of this age, particles in Fab areas weren't as well controlled and if sitting under Al tracks, they can cause this type of fail (but there are loads of other ways, such as currents pushing Al grains 'downstream').

You'd be surprised how many ic's with broken tracks you can fix by a well aimed push with a probe needle under a microscope.
 
5Hz is, IIRC, in the region of the drive frequency. But to get an observable flutter you would need more than a dropped or low phase. Either the bearing would need to be high friction or one of the phases actively working against the motion, like one of the phases being in braking mode.
 
davidsrsb said:
Has anyone seen a datasheet for this chip?
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Presuming we're all using the same google... there isn't one available. That was my first port of call obviously! If I had details I could consider making a discrete replacement. I don't believe it was used for anything other than a specific range of Technics TT's.
 
Hempknight said:
Here's a few more options after 5 mins with google, found it listed as 'AN640 IC VCR MOTOR DRIVE' can be found in these models from panasonic -
AG7110
AU700
RS1700
SL5200
SP15

And here an aliexpress link thats not been posted yet https://www.aliexpress.com/item/5pc...chweb0_0,searchweb201602_3,searchweb201603_53
Click to expand...

The last link is not the correct part. It is a 24 pin device with a metal top surface. It's used in a whole range of Technics TT's. I don't think it was used in VCR's but it is not unusual to find inaccurate descriptions of IC's. All those links say there is no stock anyway!
 
It does mean that there are old VCRs out there that are chip donors and the VCR use could also explain a Russian clone
 
VCRs have direct drive drum motors, just at a little higher speed than a turntable. I recall tin top chunky ICs driving the motors of some of the JVC/Ferguson models we made at J2T in Newhaven in my youth. Buggered if I can remember model numbers 140, 160, 170 spring to mind being numbers of JVC models, but my memory is bad
 
Woodface said:
Could this be the one occasion where Jez is wrong?;)
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Get the Guinness book people on the line!

Who knows... If it's in VCR service manuals possibly. It still seems very unlikely to me but to be honest it ain't important enough for me to start tracing through various manuals to find out.
 
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