IC-208h won't power on anymore

[VK7ZA]

It's my fault, I fiddled.

Radio was working fine, then I attempted to DIY a remote head cable as they can't be purchased any more.

Long story short, after trying my funky cable, the radio won't power on any more, so assume some pins shorted one of the other lines perhaps. Checking the schematic, there are no fuses in the head or protection diodes that I can see to check.

I did find one post on the net where the poor chap had the same issue after a dog are through the extension cable, but he didn't mention how or if he fixed it.

Has anyone else seen this happen, or able to offer a next steps to try? I've added the service manual which has the circuit and layouts to the post.

Ta,
Lance

[VK4TI]

First thing is check the power protection diode is still fine

[VK4GHZ]

I did find one post on the net where the poor chap had the same issue after a dog are through the extension cable, but he didn't mention how or if he fixed it.

Gotta love the way most people seek help on Forums like this, and then never bother to post a follow up that will help others down the track.
Has selfish written all over it.

I've added the service manual which has the circuit and layouts to the post.

Ummm, no?

If the radio has a software power switch, as opposed to a "real" power switch, and it's not turning on, that alone suggests you've blown a +5V regulator.
Check the regulator part itself, or for open circuits in the tracks coming from the regulator (tracks that weren't thick enough to survive abnormally high currents).

Rule #1: check all the voltage rails are correct.

[VK7ZA]

Thanks for the pointers Adam and Barry.

I don't know what happened with the service manual, sorry. It can be found at http://www.repeater-builder.com/icom/pd ... manual.pdf

Status update:

• I've confirmed that both power protection diodes are OK in the unit base.
• The 5V regulator in the head is fine.
• I can't check most of the reference point voltages, as they only have voltage when powered on. What I can test appears ok.
• The main CPU (IC6) in the head is getting 5V.
• The power pin (86) on IC6 sits at 5V, and pulls to ground when the power button is pressed.
• Q502 on the base should receive a voltage from the base CPU, which switches the main power on. It's not getting anything when I push the power switch, so the problem appears to be in or between the head and base CPUs. That's a bugger if the case as the base CPU has a shield soldered over it.
• The CPU in the base is getting fed 5V. Can't check any pins as such, as it's under the soldered shield. But at least I know the 5V regulator in the base is working.

Any ideas for next steps? The link between the head and body appears to be serial, so don't know how to diagnose if the signal to turn on is getting to the body successfully. Should I be able to hook a computer serial port up to the data in/out ports on the head and open it like a normal serial port and read what's coming out?

Ta,
Lance

[VK7ZA]

The plot thickens.

The head works fine, when I power it independent of the base.

I managed to expose the connection (base to head) pins while the head is connected, and noted that the 13.8 line is only hovering at .5V. Unplug the head and it goes back up to 13.8.

Hmmmm. If it were a simple short in the head, I would assume I'd have seen it when testing the head on its own. Any thoughts?

Lance

[VK7DB]

Whats R513 doing? Whats its resistance? Whats the volts drop across it with the head connected?

[VK7ZA]

Whats R513 doing? Whats its resistance? Whats the volts drop across it with the head connected?

First, the resistance values of R513, which should be 1ohm:

• No power, no head: 18k
• No power, w/ head: 160k
• w/ power, no head: 36k-45k (fluctuates)
• w/ power, w/head: open circuit (too high to measure)

Secondly, the voltage drops:

• No head: 13.94v -> 13.8v = 0.14v drop
• w/ head: 13.94v -> 0.04v = 13.9v drop

So after all of that, am I to conclude that R513 has had it, and to replace it with another 1ohm resistor? And if so, can it be substituted for a zero ohm?

I'm also interested in the purpose of the 1ohm resistor. Is it sacrificial? I understand that zero ohm resistors are used for jumpers, but don't know what purpose R513 serves in this instance.

Ta,
Lance

[VK5PJ]

Hi Lance

I'm also interested in the purpose of the 1ohm resistor. Is it sacrificial?
Ta, Lance

it would be a cheap way to fuse the line and by the look of it, it's purpose was a success as it has sacrificed its life to possibly save the rest of the radio. having low ohm resistors in vulnerable rails (exposed to humans) has become a common way to provide protection that does not cause the tracks on a PCB to burn up. In years gone by it was common to have to repair a PCB track after an incident like you experienced but that is hard work and very messy and sometimes it was a terminal event for the radio.

Hope your repairs go okay and don't put in a wire jumper unless you have a death wish

Regards,
Peter, vk5pj

[VK7DB]

^ what he said.. The 1R resistor has gone high resistance, its saved the PCB traces.. I wouldn't replace it with anything else other than a 1R resistor. Just typed all that to meet the 30 character limit.

[VK7DB]

I had a search for the correct part you need, but I cant find it at the moment.. Its similar to whats pictured below.. You just need to get some of this and put it back into R513.

[VK7ZA]

Thanks for the explanation Peter!

... and don't put in a wire jumper unless you have a death wish

Haha, that's exactly what I planned on doing. In that case I'll order some 1ohm resistors and see how I go.

Dion, I'm interested on what guided you to R513? Was it that you recognised it as a fuse? While I've debugged a fair share of electronics in the past, this would probably be the most significant one, and understanding the diagnostic process has actually been enjoyable. The stress of potentially having let the smoke out not so much.

Oh, and judging by the TFS's preparations for today's hot windy weather, there may be plenty of smoke around to catch and put back into the R513.

Lance

EDIT: Woot! I found a strip of 1ohm resistors in my box of tricks. It's a little larger but should fit on the pads so will give it a whirl.

[VK7ZA]

Adam, Barry, Dion and Peter, thanks so much for your help. If you'd be so kind as to PM me your paypal email address, I'd love to buy you each a beer or coffee. I won't be able to be with you in person, but as you sip it, you can know that your guidance was very much appreciated.

Lance, VK7LDC

P.S. If anyone has a remote cable for an Icom IC-280h that's going spare, I'd love to hear from you.

P.P.S. Because this forum isn't accessible to the general public or indexed by Google, I added an account of the salient points to by blog at http://lance.conryclan.com/home/?p=30 in case some other poor sap has the same problem down the line.

[VK7DB]

Dion, I'm interested on what guided you to R513? Was it that you recognised it as a fuse?

Had a look at the schematic, traced it back to the power supply input. Had a look at the other components and decided that the most likely to fail would be the 1R resistor.
Lets assume that the HV line got grounded. Ohms law tells us that the current through the resistor would be I=V/R = 13/1 = 13A. Then we can calculate the power dissipated in the resistor P=VxI = 13x13 = 169W. Knowing that 2012 SMD devices cant dissipate 169W, I guessed that it would be the first component in the circuit to fail.. http://pdf1.alldatasheet.com/datasheet- ... 0EZHJ.html datasheet says its good for one eighth watt dissipation. Knowing that its dissipation rating would have been immediately exceeded, I guess I did recognise it as a fuse..

[VK4TI]

Well done , good eyes and some luck is all you need

[VK7DB]

The other clue was "The CPU in the base is getting fed 5V" This means that the reg and everything upstream back to the power socket is good, including the inductors L60, L61, L62 and L63. Not much else between the power socket and the umbilical cord socket apart from R513.

[VK7DB]

The link between the head and body appears to be serial, so don't know how to diagnose if the signal to turn on is getting to the body successfully. Should I be able to hook a computer serial port up to the data in/out ports on the head and open it like a normal serial port and read what's coming out?

Likely not. What I would do is inspect the waveforms, if any, on the signal lines with an oscilloscope..