Ailtech 707, Attempt at Functional Repair - Page 1
Forum section: electronics / repair

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 08, 2017, 07:04:21 pm
content: Lets have a talk about lemons...but lemonade shall be attempted.Ailtech 707 spectrum analyzer bought for $50 off the back of someone guys truck. Condition: beat to hell, covered in gunk and and scratches with a huge gauges around the main tuning knob, and missing the bottom cover plate. Ergo it looks like shit, but it was supposed to work. What really happened was a code lemon, "it's dead Jim". But it has signs of life, it powered on, but the CRT and digital display both went nuts.The CRT problem is simple...the anode connector had popped off. However, after many times of trying to reconnect it and having it immediately pop off, it finally had enough and the wire broke. Is there anywhere I can get small CRT anode caps? Unfortunatey, I haven't found the CRT type in the manual to get the connector size, I'll keep looking though. Or...on a scale of 1 to insane, how stupid of an idea would it be to just solder the wire onto the anode?Once I get the CRT going I can check for other faults.

author: SeanB
author_rank: Super Contributor
timestamp: November 08, 2017, 07:35:34 pm
content: Would not solder it, just go find a regular small screen CRT and use the anode connector, or fashion one out of a small steel wire bent to shape to fit the cavity there. Then you can use the existing silicone cap again. The wire shape you need looks like a small W, with the ends clipped into the cup of the anode connection, and the wire is soldered to the middle of it. Soldering to the tube itself will crack the seal there and destroy the CRT immediately, plus the metal used there is a high nickel alloy, and solder will not alloy with it at all, even after you remove the black oxide coating it has on it.

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 08, 2017, 08:07:38 pm
content: Quote from: SeanB on November 08, 2017, 07:35:34 pmPerhaps I need photos. It's not a bent wire, there is a metal pin sticking out of the anode cup that the connector is supposed to clip onto with a pin socket (like a tube socket of one pin). The problem is the contacts in the pin socket have gone all floppy and won't stay on. I might try to jam something behind the contacts to keep them closed, but I'm not sure that would work. Hence, I considered soldering to the pin, or could this still bust the tube?

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 04, 2018, 07:01:52 pm
content: On a snowy winters day, I decided to have another look at the old beast. Here is the odd anode connector that needs to be bypassed or replaced. (the metal gunk sticking out is foil I tried jamming in it to make it stay on). For scale, it's about as wide as my thumb. Can anyone identify this?I had an idea for a temp fix in that I could wire rap that pin and somehow jam the other end of the wire into the ramains of the connector contacts and tape the connector over the anode hole just to keep it insulated (there is a control shaft that runs right behind the anode which is the main isolation concern).

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 11, 2018, 08:14:00 pm
content: Bahahahaaa! A piece of wire works!But it's still got lots of issues. The DIP chips have silver pins which are corroding. Reseating them seems to fix this. However, after inspecting the RF deck, the whole thing is infested with carbon comps!And yes, it's contracted the drifting disease.Several really bad ones (hundreds of percent) in the YIG VCO tuning circuits! I'm going to have to inspect all the ones in the filters and everywhere else!Does anyone know what the accepted resistor tolarance would be for something like this? I would assume they used wirewounds for anything critical, but I'm not sure. Obviously anything over 100% drift has to go, that's dogbone resistor drift levels! Filthy parasites!

author: Chris56000
author_rank: Frequent Contributor
timestamp: February 28, 2018, 12:00:46 am
content: Hi!Have you got a copy of the Service Manual and can it be found anywhere?I'd be more than willing to look over the circuits and give you a second opinion as to which resistors need to be carbon comp and which you can reasonably use carbon film in!There's all sorts of fleabay sellers advertising kits of "carbon composition" resistors but one glance at the pictures reveals they're only describing "what people are looking for" – carbon composition are always parallel–sided! I have never seen a full kit of true C.C. resistors offered in E24 from 1 ohn to 10M anywhere in goodness knows how many years – only individual values and then not many of 'em!Most C.C. resistors were only specified to +/– 10% – 5% or better tended to be special order bought in manufacturing quantities by OEMs!I'm afraid the only way round this one is to get a cheap notebook, remove the YIG modules or PCBs where the resistors are most badly drifted out of tolerance, and write a shopping list out writing down how many are needed – C.C. will have been used specifically to minimize extraneous inherent self–inductance!I would deal with the specific resistors most badly affected first, replace only these, then test your unit again between each batch of replacements, then as soon as you notice a worthwhile improvement, stop at that point!Chris WilliamsPS!http://www.justradios.com/reskits.html#kit1BWill these help?I appreciate it's a three–figure investment, but you can have the assurance that you're using fresh bits rather than ancient NOS from some long gone ancient repair shop, and should you need values below 2R2 in C.C., you can possibly buy them in 5s or 10s individually!

author: Cyberdragon
author_rank: Super Contributor
timestamp: February 28, 2018, 12:58:48 am
content: I have the original paper service and user manuals.The calibration manual is on a disk. Unless you mean you want a copy, in which case, try to keep looking online. It would be a monumental task to scan all the pages, especially since most of them are fold-out schematics, which means the big book has to be supported somehow while you scan different sections. If there's nothing online I might I have to try.If I really have to use carbon resistors, I can get them from my radio club. Although I'm assuming I can use modern resistors in all the DC YIG drive stuff?The problem is going to be two things, disassembly and re-calibration. It's somewhat modular as some sections are remove-able just by unscrewing and unplugging them. But others have soldered connections in strange places (there must be ways to remove them for access, but I'll basically have to do a total teardown). The infection has spread throughout all the filter modules too! I seriously hope there's not any inside the YIGs, from what I've seen from Signal Path, there could be bare bondwires in there!The second problem is I only have 100Mhz scopes and a 500Mhz frequency meter, so I hope there's nothing too critical beyond that.

author: Chris56000
author_rank: Frequent Contributor
timestamp: February 28, 2018, 08:33:20 pm
content: Hi!You should be OK with carbon–film resistors in the d.c. supply paths, providing the r.f. decoupling to earth is adequate!I haven't seen any service manual for the Eaton 707 as yet, but I certainly agree there could be directly bonded chips in the YIG modules to minimize stray capacitance and inductance, so unless tests or voltage readings/waveforms compared with what's in the S.M. clearly indicate a totally failed or dead YIG module causing a complete signal–path blockage, you might have to leave the internal resistors as they are!Chris WilliamsPS!I think DX Devs or k04bb would appreciate a copy of your user, service and calibration manuals, so if you can find a way to scan/upload these I'm sure there''d be many people glad of them!They might have a facility to collect the manual on loan free of charge, carry out the scanning/copying and then return your originals back to you afterwards!

author: amyk
author_rank: Super Contributor
timestamp: March 01, 2018, 02:44:03 am
content: If you have a good camera, it will be faster and easier than scanning.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 02, 2018, 02:11:52 am
content: I can try photos as a last resort. But it's on extremely yellowed paper with tiny text. So I'd have to get good lighting and focus, and I don't have super steady hands either. Of course, I could take close ups, but that would mean hundreds of photos.Quote from: Chris56000 on February 28, 2018, 08:33:20 pmI could try the local library. But they are incompetent bafoons, so I wouldn't trust leaving them there (they'd get tossed, mailed somewhere, filed somewhere, or possibly even eaten by small children)! The only other place I could think of would be the school, but either way, I don't know any place that offers free copies (I really don't want to have to pay for the amount of scans I need, unless it's super cheap and guaranteed good, which seems like a catch 22).

author: ailtechman
author_rank: Newbie
timestamp: May 13, 2018, 02:32:06 pm
content: Cyberdragon,I am one of the original techs on the 707/727. Like the units themselves I've aged somewhat but still remember quite a lot all these (45) years later. I've got 6 units here myself but it's been awhile since I've turned them on. Most all the critical resistors should be 1% wire-wound. I've heard many reports of failing tantalum caps. My particular specialty was the four analog boards, digital display and overall checkout and alignment. Can't answer much about aging components but contact me if you have specific technical questions.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 13, 2018, 10:11:42 pm
content: There are wirewound resistors. But the carbon ones aren't like 50% out, some are 100% or more out (including the one in series with YIG oscillator tuning coil), so those'll have to go. Also, where are these tantalums hiding? I only see mylar, ceramic, and electrolytic. It's also not just age that killed it, it was clearly abused (which is why it was cheap). It must have been stored in harsh temperatures (garage, shed, barn, exc.) to ruin those resistors, luckily no moisture damage.Currently it doesn't respond at all to input signal on any setting (input using single transistor VHF oscillator). I hope the input section is OK. It does show noise at the lowest frequency and lowest IF attenuation settings, which does go away when the IF is unplugged, so something is at least trying to work. There is also a low reading (a sort of hump) that hovers around a certain frequency (can't remember what) with no input. Are my YIGs at least OK if I have IF?

author: ailtechman
author_rank: Newbie
timestamp: May 15, 2018, 02:28:42 pm
content: All caps above .5 uf are probably suspect. Sorry I don't have easy access to my documentation or gear right now. For starters, Feed 21.4 mhz into the rear connector where the jumper is to check if your 21.4 IF is ok, it should be very sensitive. Do you see the zero-beat signal in band 1, that would indicate your yig is ok. Can you see anything in band 2? You might have a blown band 1 mixer, very common. You really need a comb generator to work on and align these units easily.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 15, 2018, 10:36:47 pm
content: The IF is responding. It dies entirely (no noise anymore) if the IF cable is unplugged. I don't remember what band I saw the signal in, I'll have to check again.I don't have a comb gen (or at least anything equivalent that goes above a few MHz) but I do have a (tube) VHF sweep gen. Unfortunately it's on the bench in a hundred bits due to it's tuning selector coming loose.I do have some old tube signal generators that produce lots of harmonics, and a beat frequency UHF frequency meter. Would any of that work?

author: ailtechman
author_rank: Newbie
timestamp: May 16, 2018, 08:29:04 pm
content: Please contact me offline before we boar everyone. You can continue the blog as we make progress.

author: Cyberdragon
author_rank: Super Contributor
timestamp: June 24, 2018, 08:10:42 pm
content: HOUSTON, WE HAVE SIGNAL!Alot of problems seem to be dirty contacts on everything (switches, chips and chip sockets, exc).No, it's still not OK. This is about 200MHz reading at around 99GHz (which doesn't even make sense). I also don't know the exact amplitude. According to that guy /\ in the dms, the readout runs of the YIG driver, which is messed up, so that may explain the 99GHz rubbish.NOTE: There are harmonics, but I turned down the scan width to make it clearer for the crappy samsung cam.

author: Cyberdragon
author_rank: Super Contributor
timestamp: June 24, 2018, 08:51:48 pm
content: No idea what's going on here.Zooming out reveals three signals on the display. The center one is internal as the RF attenuator has no effect. The outer two are external, touching the leads and changing the attenuator affects them, but I already ruled out wifi (or at least my wifi) as I turned it off for a bit. Feeding in the 200MHz (roughly) signal makes the outer two grow and smaller peaks appear.I'm assuming the center signal is a marker of some sort as the display is reading all 9s at this point. I'm not sure though, and the outer signals and what they have to do with the signal being input I have no idea. Mixer problems?Note: sweep width is at 30MHz (full range off), time at 3 mS/cm, bandwidth auto, video 0.5, amplitude at 2 log dB/cm, all attenuators at 0.EDIT: Pretty sure the center signal is the end of range marker now.

author: Cyberdragon
author_rank: Super Contributor
timestamp: June 24, 2018, 09:20:42 pm
content: Maybe if I changed the battery in my signal generator, it wouldn't be outputting 100MHz instead of 200MHz and interfering with a local radio station...So the machine is reading correctly, both signals were around 100MHz...always check your equipment.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 25, 2020, 01:39:54 am
content: Great...so I tried some more to get it working right (haven't ran it in a while), and the flyback overheated.The manual is for one revision older unit (did they forget to update?), so the schematic is wrong for part of the CRT supply, but it also doesn't help that there are very little voltage readings for this part of the circuit. I've checked obvious stuff like electrolytic caps and diodes, but everything seems fine. (at least under no voltage). At these voltages, it could even be a cermamic though (but again, didn't notice any obvious shorts or physical damage). The bias resistors on the base drive transistors in the astable oscillator for the flyback have gone from 470 to about 560, bad drift, but I don't know how bad that would effect it since it's just a free-running oscillator.Any ideas?