[time-nuts] EIP545A 18GHz counter query

Chris Wilson chris at chriswilson.tv
Thu Dec 6 12:33:14 UTC 2012

> 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

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

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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