Another 139XLR power supply problem.

[Handy Andy]

Low-boy,

The former posts showed a Bridge rectifier that was pretty damaged.

This is the same power supply?

So, to me this is not over, if you can't get the voltage up to 12~14 volts, then more than likely there is other damage to the power supply. (we're having that now)

I'm thinking both Zener's need to be replaced if they got full ripple current, they would cook crowbarring the ripple trying to smooth it out.

 

[Low_Boy]

I replaced D302 yesterday. For some reason unknown to me when I checked voltage on the collector of TR302 there was a spark and after checking D302 had went open. I unhooked TR401 again and tested that and TR302 both are good. Hopefully I have another replacement for D301 and will replace that like you mentioned yesterday. For some odd reason the damage originally happened when the DC power was plugged in to the back of the radio. And even after the damage you see the power supply worked perfectly. So either D301 is bad out of the package or possibly a resistor. Which all were replaced. I think I will have to do what Nomad said and check all the new parts.

 

[Low_Boy]

I happen to have no more 6.1V 1 W diodes. I do have 7.5V and 5.6V diodes. Also there are loads of 1N4735 6.2V 1 watt diodes out on the market. Will either of the ones I have work?

EDIT:: Looking back the diode I used in D301 was a 6.2V 1 W not a 6.1V.
The 6.1V diodes are pretty impossible to get.

 

[brandon7861]

6.2v will work but it will change the position of RT301. You might even get away with 5.6v if RT301 has enough adjustment range. What you could do, and what I would do in that situation, is use the 5.6v zener you have and add another diode (this one turned the other way around) in series to make 6.1v.

 

[Low_Boy]

6.2v will work but it will change the position of RT301. You might even get away with 5.6v if RT301 has enough adjustment range. What you could do, and what I would do in that situation, is use the 5.6v zener you have and add another diode (this one turned the other way around) in series to make 6.1v.

To

6.2v will work but it will change the position of RT301. You might even get away with 5.6v if RT301 has enough a

T

6.2v will work but it will change the position of RT301. You might even get away with 5.6v if RT301 has enough adjustment range. What you could do, and what I would do in that situation, is use the 5.6v zener you have and add another diode (this one turned the other way around) in series to make 6.1v.

To satisfie curiosity I removed TR302 the TIP and put in a 2SC1419. I saw one volt less coming out of TR401. Rechecked every other voltage and part. All correct but what I am seeing coming out of TR401. I am thinking (HOPING) that TR401 is bad and giving me a false reading. I really am not sure what else to do.

 

[brandon7861]

To

T

To satisfie curiosity I removed TR302 the TIP and put in a 2SC1419. I saw one volt less coming out of TR401. Rechecked every other voltage and part. All correct but what I am seeing coming out of TR401. I am thinking (HOPING) that TR401 is bad and giving me a false reading. I really am not sure what else to do.

Its super strange that TR401 would be responding to input and be bad (not impossible, but rare). Are you sure RT301 is good? That variable wasn't by accident turned all the way to one side was it?

 

[ExitThirteen]

Just as a quick check, if you have not done so already, take the positive wire that goes from the power supply board to the rest of the radio, and disconnect it off the power supply PCB, then check to see if your voltage comes up to 13-14V. I'm wondering if there's a failure on the radio's main PCB that's pulling down the power supply, I've had this kind of failure before.


~Cheers~

 

[brandon7861]

Just as a quick check, if you have not done so already, take the positive wire that goes from the power supply board to the rest of the radio, and disconnect it off the power supply PCB, then check to see if your voltage comes up to 13-14V. I'm wondering if there's a failure on the radio's main PCB that's pulling down the power supply, I've had this kind of failure before.


~Cheers~

he said it works on an external DC supply.....

 

[brandon7861]

To satisfie curiosity I removed TR302 the TIP and put in a 2SC1419. I saw one volt less coming out of TR401. Rechecked every other voltage and part. All correct but what I am seeing coming out of TR401. I am thinking (HOPING) that TR401 is bad and giving me a false reading. I really am not sure what else to do.

When you say every other voltage is correct, do you mean that the base of TR401 (yellow wire) has the expected 14.5v on it?

 

[Low_Boy]

I mean on all components that do not come off TR302 and TR401.
TR302
C..25V
E..9.62V wrong
B.. 18.59V wrong 3V high

TR401
E..9.62V wrong
C..25V
B..9.06V should be 13.8V

D302
C..19.32V
A...006V

D301
C..6.048V
A...005V should be 6.1V
In circuit shows continuity out tests good. Same voltage on TR302 and 401.

 

[brandon7861]

TR302
C..25V
E..9.62V wrong
B.. 18.59V wrong 3V high
This is a problem because the base and emitter should never be more than 0.7v apart.

TR401

E..9.62V wrong
C..25V
B..9.06V should be 13.8V
Although the voltages here are wrong, the diode drops look good and the emitter is at what it should be with respect to what voltage is presently at the base. Id call this part good.

D302

C..19.32V
A...006V
This zener is toast, you'll need to replace it. In fact, I think we found the problem, because with the regulator trying to put 13.8v out, that, on a good day would put 15.1v on the base of TR302. 19.32v-15.1v=4.22v and although that is within spec with respect to the base-emitter absolute maximum (barely), the instant the supply is turned on and before TR301 has time to react, it is greater than the absolute maximum. Replace the 16v zener, THEN, replace TR302! Right now, the absolute maximum for TR302's base is being exceeded big time! I'd bet this is due to the base-emitter of TR302 avalanching on power up...

D301

C..6.048V
A...005V should be 6.1V
These voltages look right. Zener diodes are inserted in reverse compared to the traditional diode, its the reverse breakdown that makes the magic happen. The anode SHOULD be at ground and the cathode SHOULD be at 6v

 

[Low_Boy]

I will replace D302 But this will be the second time. So if it still does not work what may be blowing D302? maybe the ones I have are bad but doubt it.
Thank You.

 

[brandon7861]

I will replace D302 But this will be the second time. So if it still does not work what may be blowing D302? maybe the ones I have are bad but doubt it.
Thank You.

What is the part number of the diodes you are using to replace D302? I would like to look at the datasheet.

 

[guitar_199]

Just as a quick check, if you have not done so already, take the positive wire that goes from the power supply board to the rest of the radio, and disconnect it off the power supply PCB, then check to see if your voltage comes up to 13-14V. I'm wondering if there's a failure on the radio's main PCB that's pulling down the power supply, I've had this kind of failure before.


~Cheers~

he said it works on an external DC supply.....

If it CAN be done.... I still see value in the test Exit 13 suggested and here is why.....
Yes he has connected a DC supply to the DC input jack and the radio works....
but .... the 13.8V DC feed from the AC power supply hooks up to the opposite side of a switch. When you plug the AC cord in ... it toggles a switch that selects whether DC ... OR regulated DC from the power supply....is connected to the rest of the radio.... if something is gooched in the side of the switch that handles the AC power supply... it could affect this.
Granted.... a few checks with an ohm meter could rule this out too.... but if something is loading down that 13.8 Regulated supply it would sure show up in this test. ( I would also imagine though that TR302/TR401 would be radiating some heat if it were the case.... but still )

 

[guitar_199]

About D302.......
I am royally confused.......
How could he be seeing 19.2 v on the cathode of D302.....
When both collectors on TR302/TR401 are 0.25v?

Where is that 19 volts coming from???
The way this circuit looks.... the nominal 24.8 that SHOULD be on the two collectors drops down through R305 (220R) ..and on to the zener.
But if those collectors are at 0.25V..... that zener wouldn't have anything on it at all.
And.....even if the zener is blown open.... that 24.8 should not be pulled down to 0.25V.

Something hiding in there......