Repairing VACTECs

[Phil Allison]

Hi,

linear opto-isolators called VACTECs are common in instrument amplifiers and other items like pedals. Many versions exist and are not so easy to buy nor cheap.

IME the most common failure is on the LED inside, going weak or open circuit, however that is something easily and cheaply fixed with a new LED.

The black plastic casing of the VACTEC can be cracked open with a bench vice or a pair of multi-grips. The faulty LED is then removed and replaced.

The LEDs used are regular, red 3mm dia leaded types with red or clear plastic housings. All seem to be high efficiency types that light visibly with the low current from a DMM on diode test range.

Install the new LED, re-assemble and finish off with a tiny drop of Supa-Glue to seal in place. Takes only minutes and is a reliable fix.

Got an old MXR " Phase 100" running nicely again yesterday.

BTW: the units have been in ( and out) production since the 1977 with almost no design changes.

https://www.youtube.com/watch?v=2EkgNPIvAi0



.... Phil

[Fox's Mercantile]

On 3/28/20 8:27 PM, Phil Allison wrote:
> that is something easily and cheaply fixed with a new LED.

That's actually quite clever.
Well done.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[Phil Allison]

Fox's Mercantile wrote:

-------------------------------

> Phil Allison wrote:
> > that is something easily and cheaply fixed with a new LED.
>
> That's actually quite clever.
> Well done.
>
>

** My next trick will be to explain how to repair an octal ouptut tube ( KT88, 6550, 6L6GC etc) when damaged by an internal arcing from pin 3 to pin 2.

Involves a hot air (paint stripping) gun, a sharp pointed jewelers screwdriver and some more Supa-Glue.

But do I actually need to?



..... Phil

[M Philbrook]

In article <738648ef-9004-42fc...@googlegroups.com>,
palli...@gmail.com says...

I have a bag of 200 RED LED clear package I got recently from Amazon.
They both work for emitter and detector althrough they are slighly
narrow beamed.

In the sun I can get a full 1 Volt out of them with out issues.

These units have flat heads on them which is most likely the resson
they are a bit picky on angle.

[Phil Allison]

M Philbrook wrote:

-------------------

>
>
> I have a bag of 200 RED LED clear package I got recently from Amazon.
> They both work for emitter and detector althrough they are slighly
> narrow beamed.
>
> In the sun I can get a full 1 Volt out of them with out issues.
>

** I have a 5mm IR LED soldered to the back of an panel mount RCA socket, so it can be linked to the input of my scope via an RCA to BNC lead.

What ever for?

It's to test the light output from IR remote controls that need servicing.

Once I am sure the IR transmitting LED in the remote is OK - I switch on a nearby portable AM radio ( tuned off station) and rely on the buzzing sound to verify operation of all push buttons.

FYI: the very fast rising edges of the current pulses in IR transmitting LED cause a tad of RFI in the AM band.



.... Phil

[John Robertson]

> ..... Phil
>

I just use a cell phone camera. Not the main camera, the one on the
screen face - it detects IR and shows flashes or steady whitish light
depending on the LED source.

Older digital phones (w/camera) and cameras show IR response, but lens
filters 'improved' over time.

John :-#)#

[Phil Allison]

John Robertson wrote:

-----------------------

>
> >
> > ** I have a 5mm IR LED soldered to the back of an panel mount RCA socket, so it can be linked to the input of my scope via an RCA to BNC lead.
> >
> > What ever for?
> >
> > It's to test the light output from IR remote controls that need servicing.
> >
> > Once I am sure the IR transmitting LED in the remote is OK - I switch on a nearby portable AM radio ( tuned off station) and rely on the buzzing sound to verify operation of all push buttons.
> >
> > FYI: the very fast rising edges of the current pulses in IR transmitting LED cause a tad of RFI in the AM band.
> >
> >
> >
> > ..... Phil
> >
>
> I just use a cell phone camera.
>

** Not near as informative as using an IR LED linked to a scope - cos

you get to see the waveform and can judge light output level.

An AM radio is also way better as you keep looking at the keys while testing and simply listen for consistent operation.



..... Phil

[Phil Allison]

Phil Allison wrote:

-------------------

>
> ** I have a 5mm IR LED soldered to the back of an panel mount RCA socket, so it can be linked to the input of my scope via an RCA to BNC lead.

** Forgot - you need a load resistor across the LED of about 22kohms.

Or else there is little or no waveform to observe.


..... Phil

[John Robertson]

> ...... Phil
>
>

Fair enough, I just use it for evidence of operation in service
applications, you are using it more for design and testing.

I will try your way out - with my storage scope I suspect I can copy the
code for transmitters that aren't standard. Not to say there are not
other methods to accomplish the same goal. Perhaps someone has an
Aurduino capture process already - I should look for that...

And, of course, some clever person has done just that:

https://www.hackster.io/techmirtz/finding-the-ir-codes-of-any-ir-remote-using-arduino-c7a852

Still scopes are fun to play with! I've been restoring an ancient
(1970s) DeVry model 34 jsut for the hell of it. It never worked because
the person who assembled it made many mistakes...but it is fine now.

Currently I am fixing a Tek 2230 with bad XY behaviour.

John :-#)#

[Phil Allison]

John Robertson wrote:

-----------------------

Phil Allison wrote:

> >>>
> >>
> >> I just use a cell phone camera.
> >>
> >
> >
> > ** Not near as informative as using an IR LED linked to a scope - cos
> >
> > you get to see the waveform and can judge light output level.
> >
> > An AM radio is also way better as you keep looking at the keys while testing and simply listen for consistent operation.
> >
> >
>

> Fair enough, I just use it for evidence of operation in service
> applications, you are using it more for design and testing.
>

** For some reason, I often get neighbor's and friend's remotes to restore to operation when keys have gone dead etc. Plus the odd IR headphone unit.

The two ideas I posted make that job VERY easy and I never charge.

> I will try your way out - with my storage scope I suspect I can copy the
> code for transmitters that aren't standard.

** I know there are two common carrier frequencies and god knows how many codes. Lost remotes a a real PITA.

>
> Still scopes are fun to play with! I've been restoring an ancient
> (1970s) DeVry model 34 jsut for the hell of it. It never worked because
> the person who assembled it made many mistakes...but it is fine now.
>

** Nice work - analogue scopes are COOL to work on.

But you need one to fix one ......

I have 6:


1. A 2MHz, 5 tube 3 inch I built as a teenager.

2. A 15MHz, 2 inch NLS Miniscope.

3. A 50MHz, BWD dual trace.

4. A 35MHz, BWD dual trace as back up.

5. A Riglol DS1052E for special jobs.

6. A 10MHz, 3 inch single trace Chinese.


BWD is an Aussie brand, now defunct.

> Currently I am fixing a Tek 2230 with bad XY behaviour.

** Needs a good talking to for that !




..... Phil

[amdx]

I did a similar thing 30 years ago when I did VCR repair. In a small
plastic box I drilled a 1/2" hole, in the box I put a VCR end sensor in
series with a resistor and 9v battery. I added two terminals to connect
my scope to. I pointed the remote at the 1/2" hole and could see the
pulse train from the remote. The problem with remotes back then was
usually the output LED solder connection.
Mikek