[time-nuts] EIP545A 18GHz counter query

[paul swed]

Very interested as I have one of these and its troubled but differently.
Can't really dig in right now.
Paul
WB8TSL

On Thu, Dec 6, 2012 at 7:33 AM, Chris Wilson <chris at chriswilson.tv> wrote:

>
>
> > Chris wrote:
>
> >>I have the 10MHz output from David's divider feeding the counter. When
> >>fed from this the Band 2 seems unreliable starting at 10MHz. If I feed
> >>it 10Mhz at 50mV from my sig gen it starts reliably. Is it a mismatch
> >>from the divider, or has it perhaps not got enough drive level?
>
> > First, what does the counter manufacturer's specification say with
> > respect to acceptable signals at the external reference input?
>
> > Second, what happens if you feed the TB output directly to the
> > counter's reference input?
>
> > IIRC, the outputs of the Partridge divider are 5V TTL from a ~50 ohm
> > source, so low peak-to-peak signal amplitude should not be an
> > issue.  If anything, the divider could be overdriving the counter's
> > reference input.  Note that the TTL signal ranges from 0V to ~+5V and
> > does not cross ground -- if the counter is expecting the reference to
> > be bipolar (i.e., if it switches on a zero-cross), it may not respond
> > reliably to TTL levels.
>
> > Beyond that, depending on how the counter terminates the external
> > reference line, you may have steps or ringing at the reference input
> > (see the thread on terminations).  Look at the counter's reference
> > input with a high-impedance (divide by 10) scope probe to see what
> > the feed looks like there.
>
> > Best regards,
>
> > Charles
>
>
>
>
> 06/12/2012 12:28
>
>
> Here's a resume of where I am at, I hope this is sufficiently on topic
> for this forum, please say if it's not. The dedicated forum for EIP
> devices seems very very quiet.
>
>
> Manual is at http://www.gatesgarth.com/EIP_545A_Service_Manual.pdf
>
> Saga starts with counter as received, showing just dashes, not able to
> do anything more than a display test, and won't perform basic 200 MHz
> test function:
>
> I have had a good look at board A108 the U6 chip is missing from, and
> apart from a mysterious pair of multi turn pots the schematic parts
> list seems to say are "not used" I can see no anomalies save for U6
> being missing altogether.... I'll post the results of fitting this
> device.
>
> The replacement for the missing U6 chip arrived this morning and it
> now completes the 200 MHz self test. It will read up to the limit of
> my frequency generator on Band 3 which is only 1040 MHz, but looks
> promising. Band 1 also works fine.
>
> Band 2 sort of works, but seemingly has a serious anomaly. I cannot
> get Band 2 to read below 185.000 MHz. To even get over 185 MHz needs a
> lot of drive power, too. 2 volts or so. Even then this somnetimes
> doesn't start a display of other than zeros. If I input 184.900 it
> won't read it and displays zeros. 185 and up is OK... Weird. IF
> frequency? It should read from 10 MHz up to 1 GHz. It'll go to 1 GHz
> plus AOK.
>
>
>
> I believe I may have isolated the issue to the A109 board. Until the
> unit warms up Band 2 is deaf and needs plenty of millivolts input to
> trigger, sometimes it won't trigger at all. Once warm it sometimes
> settles down to near the makers spec on how much input at what
> frequencies it should need to trigger. (<NOTE -- EDIT > Seems not to
> trigger at all of late, save with warming Q12) I used freeze spray to
> isolate a small area, and the fine tip of a de soldering iron
> connected backwards to the pump, so it blows a fine jet of hot air.
> The problem is in the area marked on the schematic of board A109,
> device Q12. As I have no riser board access is terribly limited.
>
>
> It's a 2N4126 component number Q12 If I just touch it with a piece of
> stiff, heavy copper wire wound round the tip of a small 15W iron, it
> changes state almost immediately and the Band 2 is very sensitive
> again, and immediately displays a frequency, down to 10 MHz, just
> fine. As soon as it cools it reverts to the insensitive state. But
> bear in mind above 185 MHz it works in a fashion hot or cold, with a
> lot of drive... If the counter is left to warm up naturally and I cool
> this device with some spray, it reads zeros again.
>
> I am not 100% sure what it's switching function is, but I have removed
> it, and isolated on my Peak semiconductor tester it varies gain form
> 170 cold to 190 warm, and it will suddenly go to a gain of just 4 if
> it gets a bit warmer still.
>
> R10 is also playing up. It should be a 43K 2% but measures 32K cold
> and warmed a touch changes to 4.8K ! It should have a 1 PPM/C
> temperature coefficient, too, so something has happened to that as
> well.
>
>
> I am not sure if any previous abuse would have damaged diode CR1,
> shown as a ND4991 ?
>
>
>
> New Q12 and new R10 fitted, problem just the same. Warming the new Q12
> brings the display back.
>
> Voltage tests done, results below all with a 30mV emf input to the
> Band 2 socket:
>
> TP2 No input signal 3.4 / 3.5V Displays zeros
> TP2 10 MHz 3.4 / 3.5V Displays zeros
> TP2 50 MHz 3.4 / 3.5 V Displays zeros
> TP2 100 MHz 3.4 / 3.5V Displays zeros
> TP2 400 MHz 3.4 / 3.5V Displays zeros
> TP2 500 MHz 0.06V Displays frequency
> TP2 900 MHz 4.9 / 5.0V Displays frequency
>
> For TP2 the change over seems circa 450MHz
>
> ----------------------------------------
>
> *** BUT *** Input 650 MHZ and TP2 shows 4.2 / 4.3V and displays zeros
> Warming Q12 makes no difference
>
> TP 3 No input signal 1.5V
> TP3 10 MHz 1.5V Displays zeros
> TP3 50 MHz 1.5V Displays zeros
> TP3 100 MHz 1.5V Displays zeros
> TP3 400 MHz 1.5V Displays zeros
> TP3 500 MHz 4.1V Displays frequency
> TP3 900 MHz 0.0V Displays frequency
>
>
> -----------------------------------------
>
> TP4 No input signal 4.5V Displays zeros
> TP4 10 MHz 4.5V Displays zeros
> TP4 50 MHz 4.5V Displays zeros
> TP4 100 MHz 4.5V Displays zeros
> TP4 400 MHz 4.5V Displays zeros
> TP4 500 MHz 4.9V Displays frequency
> TP4 900 MHz 4.9V Displays frequency
>
>
> -----------------------------------------
>
>
> TP11 No input signal 0.11V
>
> Same voltage across all frequencies Displays zeros until it gets a 500 MHz
> input, with which, and up at 900 MHz the counter displays the frequency.
>
>
> -----------------------------------------
>
> Another test:
>
> TP2 30 mV input signal @ 10 MHz 3.4 / 3.5V displays zeros
>
> Warm replacement Q12 with tip of barely hot iron, momentarily.
>
> 4.9V and displays frequency
>
> ------------------------------------------
>
> On Band 3 with no input signals to the counter TP2 shows 4.9V
>
>
> ------------------------------------------
>
> On Band 2 with no input signals to the counter TP2 shows 3.4 / 3.5 V
> (wavers about between the two).
>
>
> Q12 voltages
>
> E 12.07V no input signal : 12.08V with 980 MHz @ 50mV frequency is shown
>
> B 11.66V no input signal : 11.68V with 980 MHz @ 50 mV frequency is shown
>
> C 0.22V no input signal : 0.0V with 980 MHz @ 50mV frequency is shown
>
> C 0.22 V no input signal : 0.22V with 10 MHz @ 50mV no frequency shown
> (zeros)
>
> Warm Q12 and collector voltage starts rising instantly and around
> 0.52V the counter shows 10 MHz.
>
> Keep warming a bit more and collector voltage rises as high as 11.9V
>
> As Q12 cools voltage smoothly falls and counter stops showing 10 MHz
> frequency at about 0.52V and shows zeros.
>
> A minute or so after warming collector voltage is back down to about
> 0.22V with the 10 MHz input signal @ 50mV and counter still shows no
> frequency (zeros).
>
>
> Swapped the U2 and U7 chips over. Exactly the same, warming Q12 starts
> the counter displaying 10MHz, but only zeros until it's warmed. But TP
> goes from about 4.4V to 0.1V
>
> I am going to swap them back and repeat the test...
>
> Which I have just done and both chips are effectively operating the
> same, so I do not believe Band 2 PIA device U2 is faulty.
>
> ______________________________________________________________
>
> This is where I am now, I hope the above makes some sense if
> viewed with the service manual and the schematics. Thanks.
>
>
> --
>        Best Regards,
>                    Chris Wilson.
>
>
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