Re: 2235 Trigger on one channel

Tom Jobe <tomjobe@...>

Hi Kevin,
It's often quite easy to find out if they are fake after you get
them,'s the "how do you know before you buy them" bit that we all
need to know <G>.
The CA3102E chips are not worth much, it's the shipping charge to the UK
that will run the total cost up.
I looked at the shipping charge at some of the CA3102E links I had found
on eBay, and two of them charge less to ship than I would have to pay to
ship you the parts from California via the US Postal system. The Chinese
vendors can ship for very low costs, but then which vendor would you
trust? Maybe someone will have a trusted Chinese vendor or a better idea
about how you could get a CA3102E chip to finish the repairs your 2235?
tom jobe...

On 5/18/2017 5:46 AM, KEVIN CLARK [TekScopes] wrote:

Hi Tom :-)

As Tom indicates I am in the UK. Thank you for the eBay links. How
does one tell
if they are fake?



On 16 May 2017 at 21:06 "Tom Jobe tomjobe@... [TekScopes]"
<TekScopes@...> wrote:

There are some new CA3102E arrays on eBay.
I believe Kevin is in the UK.
Here's one from Switzerland:
Two of several from the US:
There are many available from China, some of which look like they might
not be fake.

On 5/16/2017 9:02 AM, David @DWH [TekScopes] wrote:

On 16 May 2017 14:03:52 +0000, you wrote:

Hi David

Been a little busy so took a while to get back to this. So today
lunch time I started to measure some voltages with my DMM as
suggested, results as follows, something a little amiss (I think?)

U555B Output pin 6 ch1 = 0.139V (0.2V) (0.06V error)
U555B Output pin 6 ch2 = 1.476V (2.5V) (1.02V error)

U310 Output pin 1 ch1 = -3.26V (-3.4V) (0.14V error)
U310 Output pin 1 ch2 = -2.443V (-2.1V) (0.34V error)
You can check the values of R314, R315, R317, R318, and R319 around
U310 but I think the answer is going to be that U310 is bad.

The signal into pin 1/11 is suppose to be low when channel 1 is
selected. When that happens, the output of U555B is disconnected
(pins 1/11 of U310 should not draw any current) and should reach all
the way to ground which is what we are seeing and U310 should be
working but it is not.

When the signal into pin 1/11 is high, channel 2 is selected but pin
1/11 draws more current from U555B. In this case, it is drawing too
much current indicating that either U310 is damaged or R314 and/or
R315 are open.

The fact that U555B is not reaching its full output is irrelevant
because under that condition, U310 should not be forwarding the
trigger signal anyway.

I also looked at the feed from the A3 Board Connection as follows:-

Pin 18 (6.2V) = 6.5V (0.3V error), this also shows (0V) for XY but
can't see how to check this on front panel.
Pin 32 (0.0V) = 0V
Pin 33 (5.0V) = 4.996V
Pin 34 (5.0V) = 4.996V

Some of the values are slightly higher / lower than they should be,
is this the issue?

No, nothing is wrong there.

I wonder if there are any good sources for CA3102 transistor arrays. I
do not see any so if you cannot find one, blast me an email with your
mailing address and I should be able to mail one to you. I will have
to pull it from a junked board but will test it somewhat.




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