Author Topic: IFR repair? SPECTRUM ANALYZER ! king has died  (Read 37533 times)

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Offline SArepairman

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IFR repair? SPECTRUM ANALYZER ! king has died
« on: July 08, 2013, 08:07:34 pm »
I bought a broken spectrum analyzer. The RF section on it is broke according to the self test and it does not display anything on screen.

Does anyone here have a service manual for this unit? I called up IFR and they were unhelpful, I searched google for hours and found only a users manual with no mention of any kind of service.

I am way out of my league in repairing this device. I checked the voltage inputs into the main RF can, and they seem ok. I found a sharpie X inside the RF shielded compartment where the main input leads into.

The circuit is very complicated and I feel that I will get absolutely nowhere without some kind of manual. I checked some tantalum capacitors and saw no signs of obvious damage.

target practice?
« Last Edit: October 28, 2014, 07:22:24 pm by SArepairman »
 

Online PA0PBZ

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Re: IFR 8000A repair? (manuals welcome)
« Reply #1 on: July 08, 2013, 08:27:51 pm »
Hard to make a guess when you don't know what happened to the unit, but a failing SA front end is mostly caused by too much RF on the input killing the attenuator and/or the first mixer.
Just assuming that when you say there's  nothing on the screen you mean no signal but still a straight line?
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Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome)
« Reply #2 on: July 08, 2013, 09:02:13 pm »
No, there is no line. It is just a blank display.

I proved some oscillators with my oscilloscope and the 10 and 100 mhz are working. Probing the input can output leads to noise on the oscope, IDK if it is too high a frequency (I have only a 100 MHZ scope)

Like, the text and attenuation settings and sweep width and all the controls work, the grid works, but there is no display of the signal and the self test just says RF section failed. With a big F.

When I spin the frequency knob I get some dots on the screen as it spins if the intensity is set to high.

The reference output in the front 100MHZ works fine too.
« Last Edit: July 08, 2013, 09:11:16 pm by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #3 on: July 08, 2013, 11:57:40 pm »
I found that the extension board that all the cards plug into is filthy with a black oxide. I am resoldering it all.
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #4 on: July 09, 2013, 01:53:41 am »
resoldering that board lead to the light on and inside of the YIG controller to light up. However the synthesizer one and two modules are not lighting up.
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #5 on: July 09, 2013, 01:57:28 am »
when I turn the frequency knob the dots appear all over the display, does that mean maybe there is some kind of way over loaded signal going into something ?

by dots I mean very faint dots that appear all over the screen like fairy dust or some thing.
is there any reason why there might be 16 ohms between Vcc and ground in a shielded can filled with 74 series logic?
Seems bad to me.

But then again I am not a expert at gigahertz range equipment.

there are 74LS73
74S00
74F191
and some other IC's 

all in a shielded block with ~16 ohms between vdd and gnd. Is the current In my 34401 resistance tester turning on some kind of magical RF transistor/circuit element ruining the readings?

and a SN74LS390 is reading 18 ohms in the adjacent block between VDD and ground,


ah ha.

the 16 ohm "short" is not occuring in the shielded can but something that leads to the shielded can.
I would if it is just a low value bleeder resistor. seems unlikey though.

It all leads back to the original can, there is a 25 ohm resistance between a power rail and a ground.

Hmm. I don't think the OXO is located there. Time to unscrew some hard line.

so the question is does a 25 ohm resistance belong between a power rail and ground in the RF input section (where the hard line from the input goes)?
« Last Edit: July 09, 2013, 03:24:44 am by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #6 on: July 09, 2013, 04:41:35 am »
I disconnected the suspicious RF section and I found that the voltage on the rail which goes into the 35 ohm to ground area remains at 5.15 volts, meaning that it is not a short causing a voltage rail to drop.

The 5.15 volt rails carries 100mA on it.

I don't know where to proceed from here.
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #7 on: July 09, 2013, 08:15:24 pm »
I've noticed that the red light actually turns on when things are plugged in incorrectly, so YIG controller assy is a suspect now. The YIG assy also has a weird bodge job on it, there are a few resistors and capacitors on a little board covered in electrical tape connected by long wires leading into it.. I don't know what to make of that. They could have fit in the original casing, what the hell?
 

Online PA0PBZ

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #8 on: July 09, 2013, 08:20:47 pm »
Sometimes you just need the service manual to fix stuff... From what you describe it seems that the log detector is screwed up somehow, but it could be a problem with several other sections. I am not familiar with this model, and I also could not find a lot of information on the net. However, I think you misspelled the model name and it should be an A8000?
If you are lucky there is some printing or silkscreen inside so you can at least figure out some kind of block diagram.
Otherwise all you can do is check all the supply voltages and see if there is anything strange happening there.

If the YIG is not working you'd expect a flat line, but who knows what they did in the software...
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Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #9 on: July 09, 2013, 08:33:10 pm »
Well, I hooked up an oscilloscope to the "analog video" output on the back of the unit.

The oscilloscope picks up a noise signal , and the DC offset of the noise signal is changed by the attenuation setting and the thickness of the noise signal is changed by adjusting the resolution bandwidth.

I found the manual for a similar unit, the A7750 (sorry it was the A8000 and not the 8000A), and it says that the analog video output is tapped off right before the sweep digitizer. Could this oscilloscope reading indicate that the ADC is broken?

I also noticed that pressing the Log/Lin button changes the amplitude and noise of the analog video output..
What the hell is this analog video output for? Are you supposed to hook it up to a TV?
Or is it supposed to show the spectrum analyzer display on a scope?
« Last Edit: July 09, 2013, 08:43:35 pm by SArepairman »
 

Offline dexters_lab

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #10 on: July 09, 2013, 08:48:24 pm »
My ono sokki has an analog video output mirroring the internal display
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Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #11 on: July 09, 2013, 10:48:36 pm »
do you just set the oscope time base to match the time base on the spectrum analyzer?
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #12 on: July 09, 2013, 11:36:21 pm »
great, something I did or did not do caused the cal to display fail too.  :scared:
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #13 on: July 10, 2013, 04:44:40 am »
http://www.repeater-builder.com/test-equipment/aeroflex/pdfs/ifr-a7550-spectrum-analyzer-sm.pdf

This manual has several schematics used in my unit (for instance the log amplifier board) but it is very confusing and it does not feature nice trouble shooting directions as I had hoped :(

Maybe for starters I will replace as many IC's as possible, for instance the CD4053BE (there are two different versions in the unit and a tiny bit of flux residue, I am thinking it has been replaced before) and some op-amps. I sure hope that one of these RF transistors has not broken :'(

Is the procedure for these things similar to what the president does to his cabinet after he takes office?
« Last Edit: July 10, 2013, 05:01:41 am by SArepairman »
 

Online PA0PBZ

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #14 on: July 10, 2013, 08:56:21 am »
I think a systematic approach would be better than replacing stuff randomly and hoping that helps, so start at the beginning. (Or the end...)
What is missing from the display, is it just the Rf trace? Is the text and the graticule there?

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Offline KJDS

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #15 on: July 10, 2013, 09:11:29 am »
I'd be checking the analogue output on a scope with a signal applied to the input, you should be able to see the peak. If it's there then the most likely issue if the graticule is on the display is the ADC and it's associated circuitry.

Offline KJDS

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #16 on: July 10, 2013, 09:38:57 pm »
I doubt it's the log amp.

I suspect that you have multiple issues. The spreading, rather than a spike, and it not being on frequency shouts that you have a local oscillator that isn't locked. If that hump increases when you increase the amplitude of the input then the log amp is probably ok.

If you're not getting that shape you see on the scope on your SA screen then you've also got an issue with the circuitry that goes into the ADC.

So you either have multiple circuits that aren't working as they should, or a power supply issue. The other possibility is that you have a processor contol issue, so that the local oscillators and the ADCs aren't being controlled correctly.

Can you put a function generator into the ADC instead of feeding the log amp into it? That should show as something sensible on the screen.




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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #17 on: July 11, 2013, 08:08:35 pm »
The MC12009 is a prescaler, which is nothing more than a divider and this one can divide by 5 or 6. If you wonder why it can do both 5 and 6 read a bit about about PLL circuits, it is not relevant here.

The IC is a bit special because there is a ECL-TTL level converter in there, that is why it has so many power connections.

A VCC of 4.7 volts seems a bit on the low side, did you measure the different voltages out of the power supply? It should be closer to 5 volts I think. Is the VCC of the 74 series also 4.7 volts?

If you want to know if it is still working probe the input and output with a scope and see what is going on.

If the LED is labelled LOCK I would think that is supposed to lit when things are normal, so when the PLL is locked. Not sure what they were thinking when they designed the thing of course.
« Last Edit: July 11, 2013, 08:10:27 pm by PA0PBZ »
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Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #18 on: July 12, 2013, 12:53:30 am »
When I connected a supply 5v to it (together with the 74 series which run on 4.7) I draw .25 amps from the psu but no results come of this
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #19 on: July 12, 2013, 01:34:53 am »
I think a 250 ma current draw over .7 volt increase is odd....
 Hmmm
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #20 on: July 12, 2013, 05:09:31 pm »
I replaced a busted 2n2907 transistor with a 3906 that supplied neg 12 to input attenuator. It uses a transistor BC it cuts power during mem test.. I don't think that was the hole problem but after mucking around with the iron I saw it catch a output... and then it crashed. I feel that the problem may be
 in that area
 

Online PA0PBZ

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #21 on: July 12, 2013, 05:30:18 pm »
Why cut the power to the attenuator during memory test? Makes no sense to me really.
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Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #22 on: July 12, 2013, 08:39:23 pm »
Why cut the power to the attenuator during memory test? Makes no sense to me really.

Well I thought it was odd to have a 74 series chip controlling the -12 V rail so I shorted the transistor. It failed the self check. I unshorted the transistor (the device has -12V applied to that terminal while its running) and it passed the self check, meaning that it must cut power temporarily during the check...

Any other ideas? I went after a LM380 that I thought might be bad but its not the problem. Something on the ADC side has a 20 ohm resistance to ground, but I can't find it. I did a resistance map and thought the LM380 by the input from the RF shit was the problem but the "short" is still there after the IC was removed.

When I do a resistance test across a capacitor then one way it gives me 60ohm resistance and the other way gives me a 0 resistance that eventually rises to 20 ohms.... I Checked everything in the area and it seems to be the point of lowest resistance.

The thing is its a bitch to trouble shook because the short only apears when I plug the unit into the extension board, but I unplugged every thing that I could unplug from the unit and it seems that they decided to route some kind of ground loop in a insane way, I don't know if its some star ground or what.

I also noticed that the board has a screw terminal connector that touches the ground plane by about half a milimeter. When the board is removed the screw terminal does not make a connection to ground, but when the board is inserted and the tension from the housing causes it to buckle a bit the screw terminal grounds that section. I don't know if the engineers wanted to route the ground through the housing at that point... because the ground plane was 95% removed from under the screw terminals, just the corners overlap.... but only make electrical contact while the board is under stress.


FUCK  :--

I tried putting a insulator between the screw terminal and the chasis ground incase its not supposed to make contact there but it did not matter.
« Last Edit: July 12, 2013, 08:44:40 pm by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #23 on: July 13, 2013, 02:47:03 am »

I also read the datasheet and tested that division chip, it works fine in a divide by 5 configuration, turning a 100mhz oscillation into 20mhz outputs, as per the datasheet.

I have located suspicious transistors on one of the synthesizer boards. I left a ohm meter running to measure the resistance between power rails as I plugged in various cards.

I noticed that there was a significant drop in resistance when I inserted the synthesizer #2 board. I probed around this unit and I found that there is a J310 transistor which when tested with a resistance in circuit test shows a short and when I do the diode test it shows up as a short.

http://www.fairchildsemi.com/ds/J3/J310.pdf

I am not familiar with this type of circuit element but since it is a short circuit I think it is suspicious? Or is it supposed to be SC when there is no voltage applied? The diode test works both ways on them aswell, showing 0.03V.

Am I onto something here?

The fact that all four J310's behave in the same way makes me think that this is their natural behavior but it seems odd to me. There may inductors there I suppose.... I can't get to it without desoldering shield cans on the back.
« Last Edit: July 13, 2013, 03:03:46 am by SArepairman »
 

Offline KJDS

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Re: IFR 8000A repair? (manuals welcome) SPECTRUM ANALYZER
« Reply #24 on: July 13, 2013, 08:27:51 am »
I suspect that if you check the circuitry round that, there will be an inductor pulling the gate down to the source as it's designed to be run with Vgs = 0V to simplify biasing.


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