Author Topic: IFR repair? SPECTRUM ANALYZER ! king has died  (Read 37915 times)

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Offline SArepairman

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An image of the screw holes, it just does not add up with the module, it was not meant to be here I don't think.

http://s7.postimg.org/3y18z259l/DSC_0119.jpg

also the adjust hole is unused.
 

Online PA0PBZ

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Hard to tell without seeing the SA, so I have to accept your conclusions. What you can do is look at the block diagram of the A7550 and figure out what connections (and modules?) you are missing. Still looks like its not going to be easy though.
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Offline SArepairman

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http://s22.postimg.org/4nw0mqsf3/DSC_0121.jpg

a picture showing the screw holes in comparison to the module

At most it can use two screws, I noticed some things look different then the 7550, but the marks make me nervous.
« Last Edit: July 17, 2013, 10:08:34 pm by SArepairman »
 

Offline SArepairman

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also, any idea what the screw coaxial cables are called? I need to buy two of them.

From what I see it seems that the little box on the outside contains 6 transistors of the same type and one odd ball out. I don't know if the odd ball out is the YO84 circle with a squigly line in it or the HYIA3101 transistor.

it seems to be neither because all three units connect to three different prongs of it.


what kind of component would be used here?
« Last Edit: July 17, 2013, 10:43:13 pm by SArepairman »
 

Online PA0PBZ

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also, any idea what the screw coaxial cables are called? I need to buy two of them.

The cables are called semi-rigid coax, the connectors are probably SMA.

Quote
From what I see it seems that the little box on the outside contains 6 transistors of the same type and one odd ball out. I don't know if the odd ball out is the YO84 circle with a squigly line in it or the HYIA3101 transistor.
it seems to be neither because all three units connect to three different prongs of it.
what kind of component would be used here?

The odd ball is the mixer, like the YO84. The amplifier that is behind the mixer on the other model is probably in another compartment in your A8000.
It looks perfectly fit to do the job of the missing VCO.
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Offline KJDS

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These guys do a good range of semi-rigid cables at a sensible price

http://www.gigatronix.co.uk/default.php?_minc=home

Offline SArepairman

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I found another problem on the board, a z8340B counter/timer is not outputting clocks to the ADC and dac on the sweep digitizer board, I have a suspicion that the chip I removed (hef4040) was actually getting hot because the reset pin was stuck high and it was receiving a low for the clock as the z8340B was linked directly to the HEF4040, which was over heating., unfortunately during the extraction one leg of the HEF4040 got ripped off (now I learned to use the hot air gun), fortunately it only cost 1$, so I have a replacement coming. I am in the process of studying the 8430b datasheet.

I think I might have to desolder the counter/timer chip and test it on a breadboard, trying to make sense of the commands its receiving is difficult without a logic analyzer since its a parallel chip, but perhaps the documentation will clue me in on some kind of test.


I ordered  RG-316 male-male coaxial cables on ebay, I hope they work at least to an extent. I am not sure if that could be considered semi rigid coaxial cable. I bought 2 for 20$, and I figure even if they are not ideal for the unit it should at least allow testing and maybe come in handy for something else.

Does anyone think that the HEF4040 could be damaged by having static inputs on the clock and reset pins and or cause it to experience over heating? The datasheet mentions nothing.
http://www.nxp.com/documents/data_sheet/HEF4040B.pdf

I think that this chip should be functioning even if the analog part of the board is missing the VCO because I did get it to display a trace on the CRT once.
« Last Edit: July 18, 2013, 08:48:18 pm by SArepairman »
 

Online PA0PBZ

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Does anyone think that the HEF4040 could be damaged by having static inputs on the clock and reset pins and or cause it to experience over heating? The datasheet mentions nothing.
If by static you mean 'not changing' then no, it is perfectly alright to have static inputs.
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Offline SArepairman

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Does anyone think that the HEF4040 could be damaged by having static inputs on the clock and reset pins and or cause it to experience over heating? The datasheet mentions nothing.
If by static you mean 'not changing' then no, it is perfectly alright to have static inputs.

Well then I am pretty sure it was part of the problem.
I am replacing parts down the line of some clock signals that are not going through.

Hopefully it is the 74HCT138, but I am starting to suspect the z80 cpu, which I will replace, and I will also back up the PROMS.
 

Offline SArepairman

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So I got my cables and hooked in that external module. I found that the ribbon cables cause power supply resetable fuse to blow. I hooked up the external VCO suspect in a manner so that the "slow tune" input came from the YIG filter assy and the REC IF output went to the mixer that the input goes to. I assume the YIG has the tuner voltage because there is nothing else on the board that has a coaxial SMA screw connector.


HOWEVER, there is one of those non-screw SMA connectors that is unplugged on the PC interface board, I don't know what it does but it is near some DACs, so maybe I need to connect the TUNE input using a SMA SNAP to SMA screw cable. I will study the schematic and post my analysis.

I hooked it up to a 12V bench power supply instead of using the ribbon cable and monitored the analog output, I saw nothing, however the ADC and Sweep dac are still disabled (waiting on z80 cpu and z8430 counter/timer and 74 series logic), so I don't know if I should expect any change.

I was surprised by the fact that the unhooked ribbon cables caused power supply problems, I also found it strange that the lines on the ribbon cable that are to power the VCO are only 9V and have a high ripple, I must track down these ribbon cables and perhaps replace some bad capacitors.

And of course the YIG filter has the ribbon cable thats not used either, and causes the resettable fuse to trigger. It would be nice if both ribbon cables were used (one for the external module and one for the YIG filter). I need to track them down. Maybe they are blowing for a reason.
« Last Edit: July 21, 2013, 01:29:11 am by SArepairman »
 

Offline SArepairman

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I wish I was not made a fool of, that "7th" part was actually the god damn coax connector.  |O :-DD

So the mixer is not present on the external board.
 

Online PA0PBZ

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So what you have in the 'external' module is this. Now where is the rest?
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Offline SArepairman

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God only knows!.
 

Offline SArepairman

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Here is the picture of the only unused connector in any of the RF stuff (it is a SMA screw connector in red, and the unknown bead looking thing is circled along with the connector.

I figured that maybe this is a mixer but I don't know.

The picture is of the YIG assy.

http://s23.postimg.org/qtlrlzkqx/yig.jpg

the circled unknown device looks kind of like a marble
« Last Edit: July 21, 2013, 07:50:45 am by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #89 on: July 21, 2013, 08:04:06 am »
Well, considering that the mixer should have been plugged into what that weird lever mechanism on the side is I am wondering if this spectrum analyzer is a machine off the original IFR-A8000 assembly line, modified to test the mixers. A mixer would be inserted into the thing and the machines operation would be tested?

I am suspicious of the YIG filter thing because there is no transistor after whatever that glass bead is.  :palm:

What is the purpose of the mixer in that diagram anyway, I thought it was something for mixing two high frequency signals, but it is just connected to a DC bias (2n2222) and a single input (course adjust).


I thought a mixer was a X inside of a circle anyway.....  ???

I'm guessing that the ~ in a circle is actually some kind of VCO module symbol. I would expect this to look like a silver can?
I hope in some way the YIG thing works as a VCO...

Does anyone have any ideas about something I can maybe take out of a cell phone and use in this circuit? Or some other radio device?
I can probably cast a RF can in the backyard out of aluminum. I can't find any kind of mention of a YO-92 or a Y092 VCO.

I am able to find YO92 YIG tuned oscillators, for sale on ebay though, not of the 2222 type.
« Last Edit: July 21, 2013, 08:48:00 am by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #90 on: July 21, 2013, 02:14:00 pm »
Is it normal for 6 of these RF transistors to draw 250mA when they are doing nothing?

There is only 5 ohms between the power rail and the transistor (I checked all of them, they all get equally hot), so its not just one shorting out the whole party.

I am guessing that they should probably not be getting 12 volts. Any idea how to determine the voltage for this little module?

It is possible that every single transistor in it is blown, I need to compare one to the others on the board.

god damnit, I fried one of the transistors in the external module, but its OK because I can probobly remove one from the other pathways (I don't have enough open connections to use all three outputs) and I don't have the generator.

I should probobly put a 470 ohm resistor or even a 520 ohm resistor to limit the current, so it matches up with the schematic.

the path that the transistor failed on had a cap screwed on tight to the smb connector, so it was definatly unused.   :phew:

this repair is exciting I keep breaking stuff :D
« Last Edit: July 21, 2013, 02:48:01 pm by SArepairman »
 

Offline KJDS

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #91 on: July 21, 2013, 02:59:21 pm »
It wouldn't surprise me that those FETs are taking 40mA each.

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #92 on: July 21, 2013, 05:18:16 pm »
It wouldn't surprise me that those FETs are taking 40mA each.

yea but one broke..  maybe it broke because I reversed the current for a second (I hooked up the bench supply backwords  :palm:)

When I probed them with a thermocouple I found they got to like 55C after 20 seconds of operation.

The little ribbon cable that was used for the weird lever outside the casing had a 10 ohm resistor in series with the supply on a little PCB, since I removed the module I soldered on my own chinese 10 ohm metal film resistor, which is slightly smaller and since its Chinese it does not really dissipate heat well, so it started smoking.

I know the resistor broke because I noticed suddenly it started drawing 500mA when I plugged it in, so I opened the housing an did a diode and resistance test, I found that one of the transistors on the middle path changed characteristics compared to the others, so I removed its connection to VCC and then I did a short test at 12V, the supply draw dropped to 200mA for 5 transistors.

Do you think I should put more current limiting or was it just the brief reverse voltage test that broke it?
« Last Edit: July 21, 2013, 05:23:05 pm by SArepairman »
 

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #93 on: July 21, 2013, 06:52:19 pm »
If you look at page 2-42 (page 64 in the pdf file) of the service manual for the A7550 you can see the explanation of the VCO module, the left part (the red line, see attachment) seems to be what is inside that module.

The transistors in there have a maximum Ic of 70 mA, and the normal operating range is 15-30 mA. But I can't see if the transistors in your module are the same.
And yes, you probably killed one by reversing the supply.

The circle with the ~ in it is an oscillator, in the A7550 it is the 1350-2350 VCO and it could be a yig oscillator, I don't know

One of the 3 outputs is for the tracking generator, so it is not strange that it is not connected.

Still we don't know where the oscillator is, do you have a picture of the test jig/fixture that was on the outside of the case together with that module? Does it have any connections?
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Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #94 on: July 21, 2013, 07:37:02 pm »
I read the explanation for the VCO module but I am a bit confused because there are only 2 free connections in my spectrum analyzer in the RF section, and as far as I know the VCO does not hook up to the PC control board (which has a free SMB connector on it), but I really don't think the board is rated to handle any high frequencies. It would seem to support the missing module theory.... I think that the reference oscillator module and the LO summing module were combined in my unit, but there are no free coax connectors on it. Reason for it is that one of my modules has 12 coaxes, and the LO summer has 4 and the reference oscillator has 8 in the pictures for the 7550, so 8+4 = 12, but I need to double check the schematics on it.

I know that the VCO has something to do with YIG because when I search YO92 you get some ebay results for yig voltage controlled oscillators.

30*6 = 180, 15*6 = 90, not even close to the 250 it was getting....

Here is a picture of the fixture:
Top:
http://s14.postimg.org/n9g9vfvjz/DSC_0130.jpg

Bottom:
http://s18.postimg.org/620noubdj/DSC_0126.jpg

The top (with the lever and the large coaxial screw) is connected to the module by a short piece of hard line into the input section (where the fork in the road is). The coaxial cap (and blown transistor) is in the middle fork of the road, which, if you go according to the diagrams (despite the three paths being identical) is connected to the optional generator module (J5).


The orange wire is connected to the middle two pins of the 10 pin jumper. If I measure the two free ten pin ribbon cables I find that one cable has 0V on those pins with respect to ground (floating) and the other cable has a 5.1 and a floating pin with respect to ground. However the cable which has the 5.1V is kinked in a way that makes me believe it connects to the YIG assy (I found that when the cable is inserted backwards into the YIG it allows the SA to start and does not appear to cause any problems). If I insert the other cable into the YIG (with floats on both middle pins) one way it makes a short and prevents the unit from starting and the other way it makes a sickly noise and appears to hurt the SA so I disconnect power immediately. This causes a IRF540 mosfet to over heat but not get damaged (at least as far as the diode test tells me), It is a candidate for replacement. I smelled the PCB and its defiantly the IRF540 that gave the hot plastic smell.

Considering the kinks in the cable with 5.1V I will assume that it does indeed gointo the YIG assy and that the other cable might be malfunctioning on one end, so I will now attempt to track this cable down.



« Last Edit: July 21, 2013, 08:15:11 pm by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER w/porn pg.3& YIG assy porn page 6
« Reply #95 on: July 22, 2013, 01:49:20 am »
HMMMMMMMMM this is odd.

The middle two pins on my ribbon cables might be shorting.
I measured 5.1 volts on one of the middle pins on the ribbon cable, but when I trace it back I see that there are absolutely no connections to that pin.

What the heck! I checked the cables for continuity and they seem to be fine, and I checked the cables for shorts or traces at the base (under the plastic) and they also seem to be fine.


 :-//

It would appear both of the ribbon cables are disconnected where the 12V connection to the external module would be.
This leads me to believe there is a missing ribbon cable, that perhaps goes from the YIG assy directly to the outside. Once I reassemble this thing I will probe the middle pins on the YIG for voltages.
Hmm, the ribbon cable has 5.1 volts and its connected to a switching IC.

the yig assy also has 5.1 volts, while the other cable is disconnected on the middle pins.

this mean that there is no 12V ribbon cable source for the external transitor module, meaning it must run off 5.1 volts?
« Last Edit: July 22, 2013, 04:22:58 am by SArepairman »
 

Offline SArepairman

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I replaced the 74 series chips (2x 74LS74 and 2x 74LS138 and the HEF4040 and a 74LS00.

These chips were all in line to the sweep ramp DAC (which is still undergoing shipment).

Unfortunately despite the replacement of the 74LS00 (which functions as a clock for the HEF4040) and the 74LS138's (which act as the START AND STOP signals for the clock) the sweep generator is not being activated.

However, the new HEF4040 chip is not over heating.

I am waiting in the mail for the DAC (which probobly wont fix anything), and the Z8430 and the new Z80 cpu.

An opamp which triggers the convert pulse from the video in signal is under suspicion.

I also replaced a filter capacitor on the 5V rail which was allowing too much ripple for the board, but it had no effect.
 

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER !
« Reply #97 on: July 26, 2013, 01:34:36 am »
oH MY FUCKING GOD I GOT MOVEMENT.

I REPLACED THE EVIL Z80 CPU AND NOW, DESPITE THE LACK OF A SWEEP DIGITIZER DAC, STUFF SHOWS UP ON THE SCREEN WHEN I BOOT IT.


 :o

It shows a huge trace for a second and fades

if i replace the dac and that 7400 chip I think it will be time for hard core logic analyzer use to determine whats going on.
« Last Edit: July 26, 2013, 02:17:02 am by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER ! WE HAVE MOVEMENT
« Reply #98 on: July 26, 2013, 12:22:21 pm »
I resocketed a CRT controller and now it is over heating and everything broke.


>:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:(

why would resocketing this chip cause it to short out. so weird.

from now on I will just desolder the larger dips, I guess the mechanical stress must have cracked the die or something.  :palm:
« Last Edit: July 26, 2013, 12:29:29 pm by SArepairman »
 

Offline SArepairman

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Re: IFR 8000A repair? SPECTRUM ANALYZER ! WE HAVE MOVEMENT
« Reply #99 on: July 28, 2013, 07:39:03 am »
Well I looked at  the memory of various ROM chips on this board, I found that the larger chips had what seems to be data on them, but without checksums what can I do...

There are also a few 74 series PROM's (used as lookup tables) that I need to desolder and look at. But It looks like I need a custom device to read them.
 


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