ARF 2001 in progress

[TM86]

Yep, I have one of these things. Went through and did a recap, found several bad caps that looked OK from the top, but the leads were an odd shade of green. Also had a problem with the 8 volt regulator, but a quick replacement and that's sorted now. Then found a broken coax jumper that went between the transmit board and the SWR/antenna switch board. I had a bit of coax from an SDR kit (cheap dongle, cable, rabbit ears) that I hacked up to replace that.

It's been modded for extra channels at some point in the past with a small PC board that has the two MC14008 adders on it that were moved from the PLL baord, and an extra chip (MC14081) and a transistor (2N3904) plus a few other components. Had a problem with the channels sort of jumping back and forth that I traced to a wire that had broken off the mod board.

Now for the weirdness. I went through and started checking the PLL programming, because all channels are 10kHz down from where they should be on receive. And it tracks across all 40 channels. Also, it transmits on a different frequency than it receives on, and it's a different frequency for all 40 channels that seems to follow the same 40 channel pattern. When checking the PLL N-Codes against the service manual, I found that on receive the PLL was getting the transmit N-Code (the PLL gets shifted up 455 KHz between RX and TX) and it's the correct one for that channel. On transmit, the PLL is getting an N-Code that is the same as receive +91. So it's still doing the 455 kHz shift up on transmit that it's supposed to, it's just giving a weird result.

At this point I think there's a problem on the mod board with one of the adders or the other chip. That or the darn thing was wired wrong and has always been messed up. I'm pretty sure the microcontroller is OK, but I need to figure out if it's actually putting out the codes it's supposed to. It probably is, since it seems to put out the correct patterns for tuning 40 channels with the adders doing the rest of the work.

I know the ARF 2001 is considered "rare" (although some consider it junk), but I was wondering if anyone has ever had anything like the problem mentioned above. The mod board seems to have been a popular option as I have a printed page documenting it, sort of, although I can't find a source for that. But it's enough to tell me that someone else has probably done this mod or bought a unit with it installed and may have seen this or a similar problem.

Thanks for reading my stream of consciousness post. I'll post pics of any part of the radio if you all think it will help.

TL;DR: Fancy radio broken, but not as bad as it used to be.

 

[nomadradio]

Biggest complaint I had about the ARF is that the radios were all prototypes, in effect. Never made enough of them to consider the model "mass" produced. The factory manual's list of tweaks is a hint.

Never saw that particular mod. Been too long since I saw the last one to have a clear recollection of the "simple" channel mod.

Then again, maybe it hasn't been long enough.

Field testing a prototype radio was never my favorite entertainment.

73

 

[Smokinone]

In case anyone, like me, was wondering what this rig is:

ARF 2001 SSB CB Transceiver | CB Radio Magazine

A.R.F. 2001 Scanning Transceiver by Ernie Rice KC8YOQ 2CT014 When the radio first appeared in the late seventies, I knew I had to have one, but at $1,000.00, it was far out of my reach. Here it is 2012 and I was able to obtain one. What gets your attention at first view of [...] A.R.F. 2001...

cbradiomagazine.com

Looks ompressive to be sure, I hope you get it figured out.

 

[TM86]

Well, crud. The microprocessor is bad.

I went through and removed the mod board from the equation, putting the adders back onto the PLL board like they were originally, and still couldn't get the thing to line up it's transmit and receive frequencies. Swapped the adders to make sure one of them hadn't died and the behavior didn't change. I figured if one of the adders was bad the N-Codes the PLL was getting would change when they were swapped. That didn't happen.

Then one time I powered it up and the channel display read "00", and that's all she wrote. Apparently in my playing around I managed to do something that the CMOS logic in the microprocessor didn't like and it protested in the only way it knew how.

This doesn't mean that the radio is a lost cause, however. I replaced the custom logic chip in a SBE Console V with an arduino board and I can probably do the same with this.

TL;DR: Fancy radio is now more broken than it was before.

 

[TM86]

Aaaaand, I was wrong. Turns out the 8 Volt regulator had defecated itself. Again. And this was a beefier one (1 Amp vs 0.5 Amp) so whatever I did was very bad indeed.

Swapped out the dead regulator, everything went back to where it was. So, still not working correctly but at least now it comes up with a channel display and does it's scanning thing.

So tomorrow night it's on to reading voltages on various chips channel by channel to figure out what went wrong in the math department. I'm still thinking it's the microprocessor, but I haven't actually proved that yet. I'd really like to be wrong, again.

TL;DR: Fancy radio back to less broken.

 

[TM86]

Was playing around a bit last night with the adders again. Went to put one back into the IC socket when I heard that sickening little "POP!" and a bit of magic smoke drifted up, then instead of an adder it was a very small space heater.

Found a place selling them for 65 cents each. Hopefully they're not counterfeits. I was going to play nice and just get a few but they wanted a minimum order of 10 bucks. So I bought their entire stock for $13.50.

Now, back to the chip getting fried. It may be so the microprocessor can hold the last channel it was on, but there's 8 volts on the PLL board in this rig as long as it's plugged in. I did not know that before the little boom. May also explain how I blew up the 8 volt regulator the other day. Soldering on a live circuit is generally a bad idea, whether you know it's live or not.

What I think is going on with this radio, when I'm not blowing parts up, is that the adders are doing their job properly of shifting the N-code up by a count of 91 when switching from receive to transmit. The problem seems to be that the microprocessor is also shifting the N-code by the same amount, which gives a total N-code shift of 182. Which is a little bit too much. I think I said the same thing up thread, but I only confirmed it last night, just before the little boom.

What I did learn about the microprocessor is that it was designed by National Semiconductor to be a CB specific unit. I had thought it was bespoke to ARF, but. no, they were just the only company to ever buy them apparently. So it's an off the shelf part, it's just that the shelf wasn't stocked for very long. Sadly, I haven't been able to find any technical documentation to let me know how to alter it's behavior if that's even possible. Probably not, but I'd still like to know.

TLR: Blew it up again, parts on order.

 

[Dr_DX]

@TM86,

If you need, I can un-pack mine and take some measurements. However, I haven't worked down to recapping it yet (Recapping older stuff ATM), so the measurements may be iffy. Also I work a 8 to 5 in a different field, so only have evenings to play radio. It may take me a few days to get it out and measurements taken.

 

[TM86]

@TM86,

If you need, I can un-pack mine and take some measurements. However, I haven't worked down to recapping it yet (Recapping older stuff ATM), so the measurements may be iffy. Also I work a 8 to 5 in a different field, so only have evenings to play radio. It may take me a few days to get it out and measurements taken.

Thanks. It'll be a few days at least until the parts come in. Until then I don't think I'll be doing much with it. No point without the PLL programming lines at least sort of working.

I think the only things I would need at this point would be the transmit mode PLL programming logic values for the pins feeding in to the adders (4U4 pins 7, 5, 3 and 1 and 4U5 pins 7, 5, 3 and 1) and maybe the corresponding values that are making it to the PLL programming lines for channels 1 and 40. Which by itself is a lot of work. Also, if you have a chance to look at the underside if you could tell me if pin 10 of the processor is isolated from pin 14? On this radio pin 10 was isolated and then connected to ground. It looks like it was part of the mods done, but reversing it doesn't seem to make any difference so I'm left wondering if maybe it was actually an engineering change done poorly.

 

[TM86]

New adders came in today, and they're not counterfeits! Back to square one with transmit and receive being different channels, but at least now I can start troubleshooting again.

 

[TM86]

Progress, sort of. Finally got the transmit and receive on the same frequency. It's just 825 kHz below where it's supposed to be.

Some previous owner did more than just install an extra channel mod board. This one's going to take a while to figure out.

I also found not one, but two gaps in the MSB PLL programming circuit trace. This is after removing some wires that soldered to it as part of whatever mods were done way back when. So I've patched around that but I'll probably end up laying down some new copper once I've got it on the right frequencies.

I'm beginning to understand why I got this thing so cheap.

TL;DR: One step closer to fixed, unless I blow it up again.

 

[nomadradio]

Way cool! Always thought the name "ARF" was totally appropriate.

73

 

[TM86]

I think I've figured out at least part of my problem with not being able to get this radio on the right frequencies.

I think it was modded incorrectly, but the whoever owned the radio at the time figured out a workaround and just lived with it.

There are two versions of the chassis referenced in the service manual. One with a 11.94666 MHz loop crystal, the other with a 12.0967 MHz loop crystal. The difference being that the codes from the microprocessor are higher (in decimal terms) in the radio with the 11.94666 MHz crystal, and step down by 91 for transmit, while they step up by 91 in transmit for the radio with the 12.0967 MHz crystal. That 91 is important because the PLL uses a 5kHz signal for comparison, and if you divide 91 in half, you get 45.5, which nicely lines up with the 455 kHz split I'm seeing between receive and transmit.

I did get the radio to transmit and receive on the same frequency with the mod board removed, but it was outside of the CB band and on the 0's. So a promising but false lead.

I did find that by manipulating the extra front panel switches that were added (yeah, they drilled holes in the face) I could get it on the same frequency for transmit and receive. But who wants to remember you have to flip two switches every time you key or unkey the mike? I mean, other than the guy who operated that way.

So I started looking at the mod board a little closer. One of the key components is an MC14081, which is a quad AND gate. On one of the gates I found I couldn't get an input to change, no matter what I did as far as changing available inputs. So I traced it out and found it was connected to ground. Then I looked at where it should be connected, pin 2 of 4U5, which is supposed to change between 0 and 1 when you key the radio.

No wonder it doesn't work like it should.

TL;DR: Still playing with it, getting clues as to where to go next.

 

[nomadradio]

Thank you for a reminder of why I won't mess with one of these any more. Too much like a prototype, not enough like a production radio.

73

 

[TM86]

Tonight I finally had some time and corrected that miswired gate input. Was still getting odd behavior. So I started looking at other inputs, and found one that was supposed to be wired to pin 3 on the A3 audio board had instead been connected to a toggle switch. Checked A3 pin 3 and found that it went from high to low when the radio was keyed. Visual inspection showed that pin already had solder on it from some past work. OK, I'm already moving wires so what the heck. Connected the input in question to pin 3 and now I'm off by 910 kHz between receive and transmit. Which just happens to be twice what it had been previously. What I think was happening was in transmit the microprocessor was adding 91 to it's output (at 5kHz steps, that's 455 kHz), then the adders were also putting another 91 into the mix, raising the output N-code by 182.

So I took another risk and moved pin 10 of the microprocessor back to being grounded like it was when I got the radio. Which is itself a modification because the stock wiring before traces were cut was to have it at +8 volts. Fired it up and bang, transmit and receive on the same frequency and it's not on a 0.

Which leaves me almost there, just need to figure out why I'm still 10 kHz low on every channel.

I also have to make a correction. There is no 455 kHz shift between receive and transmit for a second IF like I originally thought. This is a single conversion chassis. I'm guessing the radio designers wanted to use the microprocessor and found out after they'd settled on it that it shifted it's N-code outputs between receive and transmit and so put the adders in to offset that. Not sure if that's an elegant solution or just a brute force response.

TL; DR: Solved one big problem, now it's time to find out what's wrong with this thing.

 

[TM86]

Found the location of the problem with being 10kHz low, something in the loop crystal circuit. Found it by accident, when attaching a frequency counter probe to the leg of 4L3 closest to the crystal. Probe on, on frequency; probe off, 10 kHz low.

Now I need to figure out if that's a mechanical problem due to a bad solder joint that gets flexed when I attach the probe or if I need to somehow add a trimmer cap to the circuit.