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 <ch...@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. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.