Why use these sleeves?

[DrG]

I was salvaging an old cassette player today and noticed these sleeves (something like heat shrink tubing) on the diodes.



Why use them? They are way too short to prevent inadvertent contact - no?

On the same board, I see this one on a cap, and the leads are real long, so I suppose there is some functionality.



I don't remember seeing many of these and just wondered.

[ataradov]

Those are ferrite beads for noise/EMI suppression?

Or are they made out of plastic? It is not clear from the pictures.

The one on the capacitor looks too big to be a ferrite bead.

[DrG]

Those are ferrite beads for noise/EMI suppression?

Or are they made out of plastic? It is not clear from the pictures.

The one on the capacitor looks too big to be a ferrite bead.

Not ferrite beads (that is what I had hoped they were). these are likely heat shrink tubing or something like that - here is another shot after I removed one - absolutely plastic-like. Perhaps the instructions did not specify sleeve size or something like that and the assembler did...what he did

[ataradov]

Are they lose on the pin? I though it may be a depth indicator if they are fixed, but then it would be useful on the other pin.

It may also be an aid for some automated assembly machine. But I'm not sure this stuff is assembled by the machines.

It may be just a spacer to ensure absolute minimal pin length (may be for overheating from soldering or mechanical stress during cutting reasons), but in practice the length was selected much longer.

[langwadt]

maybe the plastic shrunk with time and heat

[wizard69]

Total speculation but the board looks like it was repaired by somebody that doesn’t know what he is doing.  The caps look especially poorly installed.   In any event my guess is that the intention is mechanical support of the devices.   

[DrG]

Yes, loose on the pin. This comes from a failed attempt to fix a cassette recorder that came out in 1987 and purchased new by me in ~1990. When I got it home, it did not work and, some 30 years later, I tried to fix it https://www.eevblog.com/forum/repair/sony-tcm-848-cassette-recorder/ but was unable to.

If this is automatic assembly in 1990, I think we have come a long way:) As for whether or not the assembler knew what they were doing, I would have to say No (see thread)

[ataradov]

I know there are Russian/Soviet standards that mandate certain spacing from the component to the soldering point. And there were standard spacers that were used to ensure that. Those were rarely used in the consumer gear though, but often used in aviation/space/military stuff.

But the same standard mandated the location of the bending point relative to the component body. In this case it is clear that nobody cared about that either.

[mariush]

Some may be ferrite beads, some may be just plastic spacers.

I'd suggest removing that yellowish material that's there just to hold components in place or prevent vibration.

Some of these substances... over time humidity gets absorbed and they become conductive, so they behave like resistors and mess up the circuit.

[David Hess]

Ferrite beads are one of the options to suppress snap recovery in a line frequency rectifier which would otherwise cause objectionable 100/120 Hz buzz.  Audio circuits are especially susceptible.  I prefer to use small capacitors in parallel or diodes which do not suffer from that problem.  It is an obscure problem.

Maybe someone replaced the rectifiers and put the tubing there in place of the original ferrite beads, or whoever assembled the board cheaped out?

[vk6zgo]

Ferrite beads are one of the options to suppress snap recovery in a line frequency rectifier which would otherwise cause objectionable 100/120 Hz buzz.  Audio circuits are especially susceptible.  I prefer to use small capacitors in parallel or diodes which do not suffer from that problem.  It is an obscure problem.

Maybe someone replaced the rectifiers and put the tubing there in place of the original ferrite beads, or whoever assembled the board cheaped out?

Or perhaps the original rectifiers were spaced off from the PCB by the tubing, with the other leads cut longer.
The person replacing them thought the tubing was there for some other reason, so included it when they fitted the new ones as now seen.

[golden_labels]

As for the hypothesis, that this is a bodgy repair: the tubes seem to be a part of the original design. Another source showing a similar thing.

[ataradov]

As for the hypothesis, that this is a bodgy repair: the tubes seem to be a part of the original design. Another source showing a similar thing.

I think this confirms the theory that they are just spacers. You can see that on that picture the lead with the spacer is much shorter. So a different person assembled it.

[dietert1]

In the case of the diodes and electrolytic caps, i would agree that the plastic sleeves work as a spacer to guarantee a minimum distance from solder point. If Sony did it, too, then it's good practice.

Regards, Dieter

[Gyro]

Yes, I agree, they are original fit spacers to ensure that the diode body doesn't drop down and sit directly on the PCB during flow soldering. This is particularly important on SRBP PCBs, where hot components need some standoff to avoid prematurely degrading the board. Sitting flush would put excessive mechanical stress on the diode body too.

[DrG]

Yes, I agree, they are original fit spacers to ensure that the diode body doesn't drop down and sit directly on the PCB during flow soldering. This is particularly important on SRBP PCBs, where hot components need some standoff to avoid prematurely degrading the board. Sitting flush would put excessive mechanical stress on the diode body too.

That actually makes some sense to me...as spacers. The use on the larger caps, however, is sporadic and the spacers are longer, consistent with lead insulators. Note though that those caps were pushed together and glued (I cleared them out to see the IC). But, you can see one cap with one spacer, and the one next to it with none and another with two.



Anyways, thanks to all for taking a look.

[David Hess]

That actually makes some sense to me...as spacers. The use on the larger caps, however, is sporadic and the spacers are longer, consistent with lead insulators. Note though that those caps were pushed together and glued (I cleared them out to see the IC). But, you can see one cap with one spacer, and the one next to it with none and another with two.

I have seen that before on parts which have thin leads.  The tubing keeps the leads from shorting together or shorting to something else.

[Gyro]

These boards got quite a lot of handling during manual assembly - anything that reduced problems due to components getting accidentally pushed would be worthwhile.

[G7PSK]

Could be that the plastic is loaded with iron dust as a cheap alternative to ferrite beads.