VHF radio repair.

[mikehibb]

Last trip out on the boat I discovered a fault on the vhf. It is a 7 year old approx Raymarine 45.
The problem is that the internal speaker has just stopped working, external speaker in cockpit still works fine.
Had a look on the Raymarine site and downloaded the manual.

The AF output amp is IC5 on the circuit, this has two outputs, int and ext. So it is apparent that as the ext output is still working that either there is a simple wiring fault between int output and speaker, or that the IC has blown one of the channels(int channel)

The wiring diagram indicates IC5 as LA 4425 however the parts list describes it as LA 4485.

A quick google indicates that both the above are 2 x 5W output amps.

However I am confused as to which one is correct, or are they interchangable?

I did find one reference to the LA 4485 having a 'mute' signal, which is also what is shown in the wiring diagram, so I would guess at the LA 4485.

Wondering if any electronics experts on the forum could confirm my thoughts either way.

Thanks in advance.

Mike.

ps, Yes I know some might suggest time to buy a new VHF, but I would really like to try and fix it myself. (I can handle a soldering iron OK)

 

[PilotWolf]

Start with the simple things - check the speaker itself still functions...

W.

 

[mikehibb]

I was going to do that anyway, I was thinking to order a new IC to take with me when next visiting the boat. For the cost of one it is easier for me to take one with me rather than try and source one when I am next in Turkey. I would spend more in fuel driving around looking to find an electronics shop.

Thanks for the tip anyway

 

[Beadle]

Before trying to change the chip I'd check out the wiring.

Its quite unusual for a chip to die for no reason.

I assume the external feed is to a jack socket. This will normally incorporate a contact which will disconnect or disable the internal speaker. This would be the first thing to check.

Secondly the mute pin would be of interest, you would need the data sheet on the chip but its possible this only mutes the intl speaker, so you might find there is a short circuit somewhere that is muting the thing..

My bet would be on something like this rather than the chip having failed.

 

[wooslehunter]

If the external speaker plugs into a jack socket and mutes the internal speaker, check the jack socket. It'll also contain a switch. If the switch portion is corroded, it may appear to the electronics that an external speaker is connected adn so mute the internal one.

 

[mikehibb]

Tthanks for the help so far.

However:

The external speaker is a separate connection, not a jack plug that mutes the internal speaker. The internal speaker should always work from the IC5 channel one output which is built in to the radio. The channel 2 for the external speaker has separate wires and the manual and wiring diagram show that this runs in addition to the internal speaker.

I am an electrical engineer, not an electronic engineer, I prefer real volts and amps, however I am pretty sure that I have narrowed down the problem to either the output stage of one of the channels of IC5 or the wiring down circuit of this (either a bad connection or a duff speaker)

What I really need help with is the difference between the two different chips that are referred to as IC5 in the manual

IC5 is an Audio Frequency Amp with 2x 5w outputs, both the LA 4425 and LA 4485 are mentioned in the manual.

The 'mute' function is not an external mute function, it is the mute signal from the CPU that mutes the circuit to the speakers when transmitting.

LA 4485 data sheet shows that it has mute function, but LA 4425 does not.

As I said earlier I would guess at the 4485 but the fact that the owners manual wiring diagram and parts list contradict each other has got me a tad confused.

Thanks again all for help so far.
I am sure that we will solve the problem eventually, hopefully an electronic expert radio Ham forum member wll pop in and read this .

 

[wooslehunter]

You can download datasheets from here and here

Essentially the 4425 is a very simple device intended for 1 speaker. It has power, group in & out pins. The 4485 is a more complex device with 2 channels. It can either be used to drive 2 speakers or on bridge mode driving a single speaker but with more power. In bridge mode, both end of the speaker are driven so neither is connected to ground. It also has a couple of extra pins for standby & mute.

If you have a DVM, check the voltages around the IC first. If you have a scope, check the audio waveforms too. It's not necessarily going to be the IC that's duff. If you can get a schematic, then it shouldn't be too hard.

 

[MarkGrubb]

Have you checked the IC for dry joints? Agree that it would be unusual for it to develop a fault for no reason.

 

[mikehibb]

Thanks again for all help.

I should have made it slightly more clear that I have the wiring diagram and the problem can only be either the IC or the down stream wiring (or the speaker)

The boat is in Turkey, I am not.

I can easily strip down the vhf and check for dry joints, wiring faults and also swap over the contacts to the known good speaker. Swapping out a new IC if that is the problem is easy enough too.

My main question was regarding which IC to buy, the 4425 or 4485.

Looks like it will be the 4485 as that has the mute function that is indicated in the wiring diagram.

I intend to buy one anyway even if it turns out not to be the fault, as it would cost me a day of driving around Bodrum trying to find an electronics shop next time I visit. Whilst I have the unit stripped down, it will be easier if I have a spare to hand if needed. I could not strip down the unit last trip as the fault only occured on my last sailing day prior to flying back home. (I have a hand held as a back up any way)

After all, one day driving around looking for parts is one day less sailing.

Thanks again all for the help

Mike

 

[William_H]

Hi Mike. You say swapping the IC would be easy. Well only if it is in an IC socket. I imagine this highly unlikely.
I would suggest that any attempt to change a soldered in IC could well result in damage to the radio which will render it useless. I reckon it would be best to use only the external output. Fit a small speaker near the radio and an external if you need it in series.
Modern circuit boards don't lend them selves to repair. A soldering Iron can be a very destructive device in amongst tiny components.
good luck olewill (The elctronics Terminator)

 

[wooslehunter]

Agree - need to be very careful when soldering a PCB. Making a joint is easy. De-soldering one is not. It really depends on what kind of board. Many boards are light brown. These are compressed paper and particularly fragile. If it's fibreglass, then it's less so but you still need to be very careful. The safest way is to clip off all the leads first & the pull each one in turn. You destroy the IC though. Then clean out all the holes either with a solder pump (sprung syringe type thing) or use solder wick. I prefer solder wick. Many prefer the pump. The key is to get the solder melted but use little or no physical force on the leads. Apply the heat for as short a time as possible. Too hot an iron & you'll strip the tracks from the board. Not enough and you won't clear the solder.