24V Radio Troubleshooting (1 Viewer)

[blastronaught]

On my PZJ70 with a 24v system, I'm trying to get the radio working. It came with an aftermarket head unit that I've never seen work or turn on. I pulled the unit and tested on a power supply per owner's manual, still no dice. The unit is specifically a 12V unit. At this point I'm ready to get a new unit, so I started probing around to ensure the power was coming in at 24V however... found 9V. After tinkering around a bit, I can get it up to 12V depending on where I pick up a ground (which I find weird but okay). Everything else in the dash confirmed 24V, like cig lighter. I dug around in the dash and I see no evidence of a voltage converter or really anything out of place or spliced in (thank god).

My question then specifically is: what is the OEM voltage provided by Toyota for the radio unit?? I found on another post someone mentioned the unit above the glove box is a converter to 12V however looking up that part number it looks like just an amp (photo below). I really expected 24V at the head unit given all the threads here about converter and load balancing devices, but I can't argue with the hard data on the multimeter.

To take the question a step further, can this 12V supply support being tapped into for a UHF/VHF ham radio unit as well? I'm sure that's asking too much from it.....

 

[jblueridge]

My 1988 BJ74 had 24V radio and tape deck. No converter or amp.

 

[blastronaught]

Sheesh, something isn't right here. More troubleshooting today. Here is a pic of that mystery box cracked open. I checked the fuse, continuity there though it does look crusty. I get a stable 24V checking across the grounded cover plate and the fuse body itself. Checking the brown and red wire out of the mosfet looking thing on the right side, which appears to be feeding the stereo head unit, I'm getting a variable output of around 1-9V, sometimes hitting as high as 12v. I checked this at the head unit pigtail as well, and I'm getting the same there. So it seems this unit is stepping down my voltage, but it isn't stable. Is this mystery box just fried?

 

[blastronaught]

From a random manual I found, this says "burehii teingu taimaa", written in katakana so it is likely something in that is written phonetically to sound like an english word. "taimaa" = timer?

 

[blastronaught]

maybe that "bu" is actually "pu", so "pure hiiteingu taimaa" = pre-heating timer, as in a module to control the pre-heating for glow plugs before starting the engine? Now I'm really confused....

 

[LDRF]

On my PZJ70 with a 24v system, I'm trying to get the radio working. It came with an aftermarket head unit that I've never seen work or turn on. I pulled the unit and tested on a power supply per owner's manual, still no dice. The unit is specifically a 12V unit. At this point I'm ready to get a new unit, so I started probing around to ensure the power was coming in at 24V however... found 9V. After tinkering around a bit, I can get it up to 12V depending on where I pick up a ground (which I find weird but okay). Everything else in the dash confirmed 24V, like cig lighter. I dug around in the dash and I see no evidence of a voltage converter or really anything out of place or spliced in (thank god).

My question then specifically is: what is the OEM voltage provided by Toyota for the radio unit?? I found on another post someone mentioned the unit above the glove box is a converter to 12V however looking up that part number it looks like just an amp (photo below). I really expected 24V at the head unit given all the threads here about converter and load balancing devices, but I can't argue with the hard data on the multimeter.

To take the question a step further, can this 12V supply support being tapped into for a UHF/VHF ham radio unit as well? I'm sure that's asking too much from it.....

View attachment 3334109

On my PZJ70 with a 24v system, I'm trying to get the radio working. It came with an aftermarket head unit that I've never seen work or turn on. I pulled the unit and tested on a power supply per owner's manual, still no dice. The unit is specifically a 12V unit. At this point I'm ready to get a new unit, so I started probing around to ensure the power was coming in at 24V however... found 9V. After tinkering around a bit, I can get it up to 12V depending on where I pick up a ground (which I find weird but okay). Everything else in the dash confirmed 24V, like cig lighter. I dug around in the dash and I see no evidence of a voltage converter or really anything out of place or spliced in (thank god).

My question then specifically is: what is the OEM voltage provided by Toyota for the radio unit?? I found on another post someone mentioned the unit above the glove box is a converter to 12V however looking up that part number it looks like just an amp (photo below). I really expected 24V at the head unit given all the threads here about converter and load balancing devices, but I can't argue with the hard data on the multimeter.

To take the question a step further, can this 12V supply support being tapped into for a UHF/VHF ham radio unit as well? I'm sure that's asking too much from it.....

View attachment 3334109

@blastronaught - I have a 93 HZJ73 with a simlar 24V-12V converter (my part number is 86206-60031 yours is 86206-60040). When I check the voltage at the radio connector, I get a constant 14V at pin 4 (my wire is Orange-Blue) and 14V at pin 3 (Red-Blue) when the key is switched on. If you are getting inconcistent voltage then your converter may be shot, or you may just have bad grounds.

If your converter is working properly, then a 12V head unit will work A-OK. Your converter is rated at 5 amps, so whatever it's powering must draw less than 5 total amps. There are a bunch of posts discussing 12V head units in 24V trucks that you can read through.

 

[jblueridge]

Yes, my pre-heater's timer box is located above the glovebox plastic bin as in your picture.
Seem like you could get a new 24V-12V converter and mount it where the old one was.
Engineer8000 here on MUD might be able to troubleshoot the box you have.

 

[blastronaught]

Thanks for the confirmation guys. From googling 70 series parts, I think the module in question is indeed a 24-12V converter and the preheat timer module is in a different location in my particular case. I also agree the converter in question is likely fried; I don't think anything would require a swinging voltage from 1-12V. New plan of action is to buy a 24V stereo (cause why not, less current draw seems always a good idea) and install a separate 24V DC - 12V DC converter directly from battery terminal with a manual switch inline to power the ham radio. Going this route instead of a relay since I'd like to be able to independently turn the radio on while the vehicle is off. I'll start a new thread once I pickup those components for anyone following along.

 

[jblueridge]

Smart.