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Post by BBB on Nov 16, 2013 13:07:02 GMT -5
Picked up a $5 fleabay Courier Classic III 23 channel crystal controlled radio that shows a DC short as soon as I plug it into a 12 VDC power supply. Happens even with the radio power switch in the Off position for that full Zero-Five effect  I now see that the 12+ goes right to the chassis instead of going thru the power switch. I started taking the power jacks apart to see if anything was visually obvious, but they looked okay and nothing is burnt on the board. Maybe one of the disk isolation filter caps I see around the perimeter that connect from the board to the chassis shorted? This unit has a base AC power supply also. I have not found the AC power cord for it yet, but I know I've got one as it is the type of cable that activates a switch in the jack as you plug it into the radio to disengage the 12 VDC power jack. I think I'm going to need to find the short before I even try the AC side. The radio has got some weight to it and is just a hair smaller than a "full sized" mobile rig. It's got a huge Sanyo brand side-firing speaker and seems to be quality made. Hopefully it will clean up well with all that 360 degree shiny factory chrome treatment.  |
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Post by libslayer on Nov 16, 2013 14:32:23 GMT -5
I'm liking the simplistic look of the radio...good luck with repairs.
KATO808 #DeepInTheHeartOfTexas
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Sandbagger
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Post by Sandbagger on Nov 17, 2013 9:45:46 GMT -5
Picked up a $5 fleabay Courier Classic III 23 channel crystal controlled radio that shows a DC short as soon as I plug it into a 12 VDC power supply. Happens even with the radio power switch in the Off position for that full Zero-Five effect I now see that the 12+ goes right to the chassis instead of going thru the power switch. I started taking the power jacks apart to see if anything was visually obvious, but they looked okay and nothing is burnt on the board. Maybe one of the disk isolation filter caps I see around the perimeter that connect from the board to the chassis shorted? This unit has a base AC power supply also. I have not found the AC power cord for it yet, but I know I've got one as it is the type of cable that activates a switch in the jack as you plug it into the radio to disengage the 12 VDC power jack. I think I'm going to need to find the short before I even try the AC side. The radio has got some weight to it and is just a hair smaller than a "full sized" mobile rig. It's got a huge Sanyo brand side-firing speaker and seems to be quality made. Hopefully it will clean up well with all that 360 degree shiny factory chrome treatment. Sounds like the classic polarity diode short. There should be a diode that spans the + and - lines somewhere along the positive rail before you get to the on/off switch. That diode is supposed to protect the radio from the effects of reversed polarity, by conducting and blowing out the fuse. But if some knucklehead replaces the fuse with a 20 amp version, the next thing to go will be the diode. Once it shorts, it'll show short in either polarity. You can simply cut the diode out and you'll be fine. But if you run it mobile, replacing the diode would be a good idea in case you have an "ooops" moment somewhere down the line..... |
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Post by BBB on Nov 17, 2013 11:30:02 GMT -5
Thanks Sandbagger. I'll check that out.
I found the schematic on CB Tricks.
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Sandbagger
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Post by Sandbagger on Nov 17, 2013 13:47:49 GMT -5
Thanks Sandbagger. I'll check that out. I found the schematic on CB Tricks. The diode you want to check is D705. It also looks like that is taken out of circuit when the AC cord is plugged in. |
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Post by gator7 on Nov 24, 2013 8:05:59 GMT -5
To bad they put the PA in the 22A position. You would of had channel 24. I like the slide controls on that rig. Nice look. I don't remember that radio from back in the day. But then again there is alot I don't remember from back then. LOL.  |
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Post by BBB on Nov 24, 2013 10:02:19 GMT -5
I replaced D705 that was indeed shorted. It shorted out again and blew a 4 amp fuse as I applied 12 VDC. I used a 1N4006 diode so I'm going to have to look deeper to see what is taking it out. Maybe need a bigger diode. The original Sanyo one was sort of cone shaped. Seeing a lot of Sanyo parts in this rig... It appears that the supply polarity is correct but I'm going to have to double check that against the schematic also (ie: the red wire in the back of the radio's standard DC jack goes to the red wire on the DC supply wire) I read that the radio could be used on neg. or pos. grounded vehicles. I'll also find a suitable AC power cord and try that but I want to see why the DC side is failing. www.cbtricks.com/radios/courier/classic_3/index.htm |
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Sandbagger
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Post by Sandbagger on Nov 24, 2013 16:40:16 GMT -5
I replaced D705 that was indeed shorted. It shorted out again and blew a 4 amp fuse as I applied 12 VDC. I used a 1N4006 diode so I'm going to have to look deeper to see what is taking it out. Maybe need a bigger diode. The original Sanyo one was sort of cone shaped. Seeing a lot of Sanyo parts in this rig... It appears that the supply polarity is correct but I'm going to have to double check that against the schematic also (ie: the red wire in the back of the radio's standard DC jack goes to the red wire on the DC supply wire) I read that the radio could be used on neg. or pos. grounded vehicles. I'll also find a suitable AC power cord and try that but I want to see why the DC side is failing. www.cbtricks.com/radios/courier/classic_3/index.htmAre you sure you put the diode in the correct way? The only way you would short that diode out (assuming it's the proper rating) is if it's forward biased. If it's in the correct way and the proper polarity is applied (reverse bias), the diode should not blow. What happens if you simply remove the diode, is the radio still shorted? There might be something else shorted in there (although that still shouldn't short out the protection diode). The cathode end (the one with the stripe) should be to the positive side. |
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Post by BBB on Nov 25, 2013 12:31:23 GMT -5
I'll try and fire it up without the diode in there. Understood, I bet something else is shorted. The original diode was cone shaped with no typical stripe on it so I went with the orientation of the silkscreen on the board for the new diode orientation. It's still on the bench so there's hope,  |
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Post by BBB on Nov 27, 2013 10:03:45 GMT -5
Went in a little deeper and something is still shorted out past the power two supply sections. (one direct the other 120VAC-12VDC built in)
I saw on the schematic that certain sections of the circuitry were isolated by a single resistor in series with the +12VDC power source and was wondering if I can simply lift said resistor(s) to help isolate the various sections to see which one(s) are causing the short?
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Sandbagger
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Post by Sandbagger on Nov 27, 2013 13:16:12 GMT -5
Went in a little deeper and something is still shorted out past the power two supply sections. (one direct the other 120VAC-12VDC built in) I saw on the schematic that certain sections of the circuitry were isolated by a single resistor in series with the +12VDC power source and was wondering if I can simply lift said resistor(s) to help isolate the various sections to see which one(s) are causing the short? This short to ground, does it go away if you turn off the power switch? If not, there are only a few things that could be causing the problem. Assuming you completely disconnect the AC power supply when the DC cord is installed, the polarity diode, a disk cap and the power socket itself are the only parts before the power switch. If the short does go away when the power switch is turned off, then the short is on the other side of the switch, and if it truly is a "dead short" (less than 5 ohms), then there is only a few things that could cause this and they are in the audio amp section, including the output transistors, and an electrolytic cap. The RF final could also short, but you'd be looking at it through a diode which should only show low resistance in one direction only, and not a dead short. |
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Post by BBB on Nov 27, 2013 14:15:24 GMT -5
After lifting the diode mentioned before the radio would now not short out until it was turned on by the front power switch. Lights came on for a few seconds then the 4 amp fuse would blow.
Just saw a few inline resistors (R914,R924,R926) in the diagram that appeared to be able to be lifted to isolate a particular section of the board, almost like they were there for protection on that b+ branch feed to that circuit. Looked like a simple way to isolate an entire section of the circuitry to narrow down the short.
I'll give it a try and thanks for the heads up on the other items to look for.
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