Repairing VACTECs

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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.

....   Phil  

Re: Repairing VACTECs
On 3/28/20 8:27 PM, Phil Allison wrote:
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That's actually quite clever.
Well done.

"I am a river to my people."
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Re: Repairing VACTECs
Fox's Mercantile wrote:

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** 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  

Re: Repairing VACTECs says...
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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.

Re: Repairing VACTECs
M Philbrook wrote:


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** 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  



Re: Repairing VACTECs
On 2020/03/29 1:12 p.m., Phil Allison wrote:
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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 :-#)#

Re: Repairing VACTECs
John Robertson wrote:


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** 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  

Re: Repairing VACTECs
On 2020/03/29 5:27 p.m., Phil Allison wrote:
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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:

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 :-#)#

Re: Repairing VACTECs
John Robertson wrote:

Phil Allison wrote:

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** 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.  

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

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** 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.  

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** Needs a good talking to for that !  

.....   Phil  

Re: Repairing VACTECs
Phil Allison wrote:


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

  Or else there is little or no waveform to observe.

.....    Phil  

Re: Repairing VACTECs
On 3/29/2020 3:12 PM, Phil Allison wrote:
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   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.

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