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Isotech ISR420 scope.

 
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Isotech ISR420 scope.

Post by Rebel Rafter » Thu Mar 05, 2015 8:33 pm

Hi, everyone, RR here again. Does anyone out there have or know where I can get a little EHT transformer for an Isotech ISR420 oscilloscope? I got one of these compact portable 20 MHz scopes with a minor fault, only an o/p transistor failed in the X o/p. This was an easy fix once I managed to get some replacement transistors, they were a bit like the ones used as video o/p's in the 70's. But when I tried to use it for the first time it failed again and this time it was the most elusive part of all which had failed, the EHT transformer. And of course it raises the age old servicing question, did it die or was it killed? Has anyone out there had any experience of these scopes and do you know if there is anything else I should check before fitting another transformer if I can ever get one. Any help most appreciated. Thanks. RR.

 
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Re: Isotech ISR420 scope.

Post by Ed Dinning » Thu Mar 05, 2015 9:47 pm

Hi RR, if it can be easily taken apart it can be re-wound. Unfortunately these parts are often potted and this then cannot be done, you will need to find another.
However, if this scope uses a voltage multiplier, that may be the part at fault and they can be fixed. What does the circuit show?

Ed

 
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Re: Isotech ISR420 scope.

Post by Alistair D » Thu Mar 05, 2015 11:56 pm

Not sure if Isotec was exclusive to R.S. components but they certainly sold the brand. Perhaps their technical department could give you a clue to the original manufacturer.

Al

 
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Re: Isotech ISR420 scope.

Post by Rebel Rafter » Fri Mar 06, 2015 12:04 am

Alistair D wrote:Not sure if Isotec was exclusive to R.S. components but they certainly sold the brand. Perhaps their technical department could give you a clue to the original manufacturer.

Al

Hi, Alistair. I did contact RS when I got the scope ages ago but they couldn't help, possibly because I didn't buy it from them or because it was out of warranty. RR.

 
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Re: Isotech ISR420 scope.

Post by Rebel Rafter » Fri Mar 06, 2015 12:18 am

Ed Dinning wrote:Hi RR, if it can be easily taken apart it can be re-wound. Unfortunately these parts are often potted and this then cannot be done, you will need to find another.
However, if this scope uses a voltage multiplier, that may be the part at fault and they can be fixed. What does the circuit show?

Ed

Hi, Ed. The transformer was definitely knackered. I know, I unwound it, carefully noting the winding details with the intention of rewinding it, but it needs special tape inserting in between the layers of the HT secondary and I don't think I have the skill to do that, especially with such fine wire. I once wound a coil only to have it fry. I've wound coils before but I've never had to insert tape between the layers. I don't like messing with anything I'm not totally confident with. I won't be buying any more Isotech gear again, that's for sure. RR.

 
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Re: Isotech ISR420 scope.

Post by Refugee » Fri Mar 06, 2015 2:23 am

This is the stuff you need.
http://www.ebay.co.uk/itm/High-Temperat ... 0953222166
I have got three transformers on the to do pile and an almost complete home made winder to do them with.
One of them is indeed a scope PDA transformer.

 
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Re: Isotech ISR420 scope.

Post by Ed Dinning » Fri Mar 06, 2015 9:06 pm

Hi RR, tape is not necessarily a high temp one, it could be standard Type 56 tape, either yellow or black and pretty thin. it will withstand about 2Kv/ layer. The area to be careful with is the edges as a turn can easily "fall down" the side and cause problems.
Dunk in molten paraffin wax when finished, this will also help insulation.

Ed


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