help with circuit repair

[JB Haskins]

I have a small, handheld geiger counter made by a firm called RDX
Nuclear (model is DX-1). Unfortunately, a much younger family member
than I decided to try putting a 9V battery in it, but he put it in the
wrong way before I could intercept him. Now, when the activation button
is pressed, all I'm getting is a constant tone. Within the tone, I can
hear individual clicking as if it is still taking counts, but that's it.
Also, the indication needle is pegged. Here is an image of the top of
the circuit board:

https://i.imgur.com/kSHzB0T.jpg

Unfortunately, I've never seen a schematic of this unit on the web even
though it seems to be sold all over the place. Contacting RDX, all they
want to do is replace that tiny board... for $120. So, if you hooked it
up backwards, what would you check first? I did check the diodes and
they all seem fine.

[Phil Allison]

JB Haskins wrote:

=================

** The CMOS IC is the most likely be damaged.


..... Phil

[JB Haskins]

Thank you, that's what I have suspected as well.

[Rich]

JB Haskins <hask...@lormail.net> wrote:
> https://i.imgur.com/kSHzB0T.jpg
>
> Unfortunately, I've never seen a schematic of this unit on the web even

Given the seeming simplicity of that board in your image (it appears to
be a single sided board) have you considered investing a moderate
amount of time into reverse engineering a schematic by following which
traces on the underside connect to which components from the top?

[Trevor Wilson]

**As Phil has stated, the 40106 is likely to be toast. For less than 10
Bucks and 20 minutes work, you could replace every semiconductor in the
thing.

--
Trevor Wilson
www.rageaudio.com.au

--
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[JB Haskins]

The last time I tried to do that, it turned out to be a disaster
although what I tried it with was a little more complex. Still, I might
give it a go with this one. I already ordered a replacement IC and the
transistors on the board- all are common parts and not expensive.
Actually ordered more than one of each since I own at least two of these
geiger counters.

[JB Haskins]

On 2/15/21 6:47 PM, Trevor Wilson wrote:
> On 16/02/2021 8:08 am, JB Haskins wrote:
>> I have a small, handheld geiger counter made by a firm called RDX
>> Nuclear (model is DX-1).  Unfortunately, a much younger family member
>> than I decided to try putting a 9V battery in it, but he put it in the
>> wrong way before I could intercept him.  Now, when the activation
>> button is pressed, all I'm getting is a constant tone.  Within the
>> tone, I can hear individual clicking as if it is still taking counts,
>> but that's it.   Also, the indication needle is pegged.  Here is an
>> image of the top of the circuit board:
>>
>>   https://i.imgur.com/kSHzB0T.jpg
>>
>> Unfortunately, I've never seen a schematic of this unit on the web
>> even though it seems to be sold all over the place.  Contacting RDX,
>> all they want to do is replace that tiny board... for $120.  So, if
>> you hooked it up backwards, what would you check first?  I did check
>> the diodes and they all seem fine.
>
> **As Phil has stated, the 40106 is likely to be toast. For less than 10
> Bucks and 20 minutes work, you could replace every semiconductor in the
> thing.
>

Quite true, even without a schematic, none of the parts are uncommon or
costly so ordered the IC and all the transistors. I got seconds because
I have at least one other of these units.

[JB Haskins]

And I just got done putting a socket in there for the IC in case any
future accidents happen, the job should be simpler.

[Phil Allison]

JB Haskins wrote:

==============

> And I just got done putting a socket in there for the IC in case any
> future accidents happen, the job should be simpler.

** Install a 1 amp diode in reverse across the batt connection while you are at it.

Only fools design such items with no reverse batt protection.



..... Phil

[JB Haskins]

Good idea, thanks, will do that.

>
> ..... Phil
>

[Newdo]

Please remember to remove the loose screw underneath the pcb

-UP

[JB Haskins]

On 2/16/21 4:34 AM, Newdo wrote:
>
>
> Please remember to remove the loose screw underneath the pcb
>
> -UP

Very observant! That's actually the pcb board screw and there so I
don't lose it (unfortunately, I have a habit of losing screws).
Luckily, the only way to power it on is by having the board re-secured
with that screw so no worries.

[Rich]

JB Haskins <hask...@lormail.net> wrote:
> don't lose it (unfortunately, I have a habit of losing screws).

Small medicine bottles make good screw holding containers.

Of course, you then have to not lose the small medicine bottle
containing the screws.

[Peter W.]

> Of course, you then have to not lose the small medicine bottle
> containing the screws.

https://www.amazon.com/Staineless-Magnetic-Screws-Holder-Holding/dp/B00NF0LH18

Comes in various sizes and configurations. That my bench also has a sheet-metal insert under the working surface also helps. Yes, the insert is fully insulated electrically.

Peter Wieck
Melrose Park, PA

[root]

Better to stick a refrigerator magnet to the case and
put the screws on the magnet.

[Peter W.]

> Better to stick a refrigerator magnet to the case and
> put the screws on the magnet.

Clearly there are no cats in your household.