Philips N4308 capstan flywheel cracking

[dazzlevision]

Hello,

I have just completed the restoration of an N4308/55 tape recorder.

I have serviced several of these over the years, but this is the first to exhibit cracking of the cast metal capstan flywheel.

Luckily, I have a spare capstan flywheel in good condition, but I noticed that the cracked one had a green paint spot on it, whereas my spare has a red spot on it.

I'm guessing this is some sort of grading mark used by the flywheel casting manufacturer or Philips during the assembly of the recorder. Does anyone have any information about this?
Nothing is mentioned about this in the official UK Philips service manual for this model.

Thanks,

Dazzlevision

[Jimmyhaflinger]

Is this a mk1 or mk2 machine?

I haven't yet seen a cracked flywheel in a 4308 but since they're made out of mazak that's definitely possible if they made a batch of them with excessive impurities in the alloy

[dazzlevision]

Is this a mk1 or mk2 machine?

Hello Jimmyhaflinger,

My N4308/55 has date codes from 1971.

I'm not sure what "Mk 1" and "Mk2" versions means, but my N4308/55 has the original knobs with a clear plastic skirt and the tape up clutch drive doesn't come from the motor pulley, but from the pulley that couples the large long main drive belt (on top of deck) to the capstan flywheel belt (on the underside of the deck).

As I understand it, there are three versions of the N4308:

The first has the tape up clutch drive from the motor pulley

The second has the tape up clutch drive from the pulley that couples the large long main drive belt (on top of deck) to the capstan flywheel belt (on the underside of the deck).

The third has different style control knobs (no skirt and black insert discs in the tops) and tape transport "piano" keys and there is no large brushed aluminium escutcheon/trim over the deck top brown plastic cover (in the area that the tape spools/turntables occupy).

Regards,

Dazzlevision

[Jimmyhaflinger]

The one with the different knobs and black trim is what i call a mk2, it also used a different speaker which wasn't quite as good as the older one

[dazzlevision]

One other thing I have noticed with this particular example, is that the decaying black "goo" of the original drive belts has affected the deck metalwork - see photo. Cleaning off the "goo" still leaves a ghostly trail where the "goo" had deposited over time, with years of no use (but stored horizontally)!

However, the only "rubber" part that hadn't turned to goo was the supply turntable pause brake block.

[Jimmyhaflinger]

The melted rubber is somewhat corrosive and has always left a mark on the nickel plated metalwork in all philips machines i have restored

I was lucky in that all of my 3 n4308s had the ivory rubber clutch elements which are still like new

[Boater Sam]

I was lead to believe that the black goo from decayed rubber contains Hydroflouric acid, do not get it under your nails, you can lose fingers.

[Sideband]

That stuff was used for etching PCB's....nasty but I've never heard of it in that rubber goo....and I've had it on my fingers many times (not deliberately of course but it gets everywhere! Not had any problems but it's a b****r to get off your fingers.

[crackle]

There was thread a long time ago about the black goo which forms when rubber drive belts degrade. It advised that to clean it use Swarfega, neat. I found it hard to believe as I thought it would be insoluble, but I tried it and it worked.
The only stuff I have found to effectively remove it.

Mike

[ricard]

I think ordinary kitchen degreaser is surprisingly effective too.

[ben]

I have seen flywheel cracking on some Spanish Ingra recorders. A similar thing happened to (of all brands) a Tandberg motor rotor!

I expect it is just a case of impurities coupled with heating /cooling cycles over time. Bit worrying though, as it's not as if you can nip down to Maplin and get another!

[ricard]

It's true it can seemingly strike randomly at any time, but if the frequency is small enough, it's like the failure of any part - things can crack or break for various reasons. It's when the frequency becomes high enough that it starts to become an annoyance (in the sense that 'I've found this old machine, most likely it won't work due to the XXX part having failed') - like the infamous cams in Akai machines, or the die cast parts in certain generations of Grundig machines (TK46 etc), where you're hard pressed to find a machine with all parts intact these days.

[The Philpott]

The hydroflouric acid caution relates to the warning not to touch burnt out vehicles as they will contain synthetic rubber hoses and seals that have become uber-corrosive in the fire.

Regardless of whether this also applies to age expired components, i will not be touching any such black goo any time soon.

[dazzlevision]

"Does anyone know why the capstan flywheels are colour coded?

Inoticed that the cracked one had a green paint spot on it, whereas my spare has a red spot on it.

I'm guessing this is some sort of grading mark used by the flywheel casting manufacturer or Philips during the assembly of the recorder. Does anyone have any information about this?
Nothing is mentioned about this in the official UK Philips service manual for this model."

However, the Dutch version of the original N4308 manual may have had supplementary sheets added, as modifications were introduced during the course of production. These were probably numbered as: Bc814, 845, 853, 900, 904, 951, 959, 990, 1021 and 1312.

Would any of our mainland Europe members know anything about these supplement sheets/modification bulletins?

Thanks,

Dazzlevision