Realistic TRC-448 not working....why?

[Turbo T]

D244 could be shorted.

Jim...question on this, I remember diodes are supposed to show continuity one way but not the the other, but do they have to be unsoldered from the board for an accurate check?

If not I checked it by putting the multimeter in the diode position, and I got zero ohms no matter which way the leads were installed....so I'm guessing the diode is shorted...?

Also I tried checking the resistors, and R314 shows 12.1 on the side where soldered to the collector track, but I was not getting a reading out of it on the other side. R315 I got 12.1 on the side where it's connected to the board where C346 is, but it looks like the other side of R315 is soldered to the track that has emitter and it doesn't look like I'm getting anything....so possible bad resistors too?

 

[slprydk]

Jim...question on this, I remember diodes are supposed to show continuity one way but not the the other, but do they have to be unsoldered from the board for an accurate check?

If not I checked it by putting the multimeter in the diode position, and I got zero ohms no matter which way the leads were installed....so I'm guessing the diode is shorted...?

Also I tried checking the resistors, and R314 shows 12.1 on the side where soldered to the collector track, but I was not getting a reading out of it on the other side. R315 I got 12.1 on the side where it's connected to the board where C346 is, but it looks like the other side of R315 is soldered to the track that has emitter and it doesn't look like I'm getting anything....so possible bad resistors too?

Pull C328 and D244 and see what part is shorted out of circuit. with the 2 parts out you can check the resistance of R314, R315 seems to be passing voltage to the regulator so it may be okay.

Jim

 

[Turbo T]

Pull C328 and D244 and see what part is shorted out of circuit. with the 2 parts out you can check the resistance of R314, R315 seems to be passing voltage to the regulator so it may be okay.

Jim

Jim,

I pulled D244 and check it with the diode side of my multimeter....zero ohms either way the leads are put on....so shorted diode, but how? Someone hook the radio leads up backwards?

I also checked R314 with it still on the board, got 0.38 ohms either way the leads were connected.

I actually forgot how to check capacitors...:redface:

What should I check next?


EDIT: I found this site: http://www.squidoo.com/how-to-check-capacitor, and pulled C328, put my multimeter on 200k and the cap dropped down and then started climbing back up the longer I held the leads on the terminals.

 

[slprydk]

Jim,

I pulled D244 and check it with the diode side of my multimeter....zero ohms either way the leads are put on....so shorted diode, but how? Someone hook the radio leads up backwards?

I also checked R314 with it still on the board, got 0.38 ohms either way the leads were connected.

I actually forgot how to check capacitors...:redface:

What should I check next?


EDIT: I found this site: How To Check Capacitor - Electronic Repair, and pulled C328, put my multimeter on 200k and the cap dropped down and then started climbing back up the longer I held the leads on the terminals.

Sounds like the diode is done, replace with NTE5074A or a 11v 1 watt zener.

R314 should read about 380 ohms in circuit so .38 in what range??? If its .38k ohms you are okay, if its .38 ohms the transistor is gone too, that is a 2SD526.

If the cap charges up into the meg ohms it should be okay, replacement on a radio this old is suggested but up to you.

Where this is in circuit hooking the radio up backwards could have done this, but something shorted down the road could cause it too. you wont know until you get the power supply up and running.

 

[Turbo T]

Sounds like the diode is done, replace with NTE5074A or a 11v 1 watt zener.

R314 should read about 380 ohms in circuit so .38 in what range??? If its .38k ohms you are okay, if its .38 ohms the transistor is gone too, that is a 2SD526.

The resistor reading of .38 was with the multimeter in the 20k ohm position.

I'll drop by Radio Shack tomorrow and pick up a diode and post back when it's installed.

 

[slprydk]

.38 ohms in the 20K range is fine.

Did you get the diode yet?

 

[Turbo T]

.38 ohms in the 20K range is fine.

Did you get the diode yet?

No not yet. Radio Shack only sells the diodes online, and not in the store. I do have them on order though, probably won't get it until next week as I received a confirmation of a Fed Ex shipment out of NJ today.

I can't wait though, I'm ready to see if it will make this radio live again.

 

[Turbo T]

Ok....well I installed the new diode and it powers up. I get lights and sound.

The PA side of the house works good.

At first I tried hooking the radio up to a mobile mag mount I had sitting on the bench, and was using my scanner and my base rig to monitor.

At first on USB I could get anything and it was a dirty overmodulated signal. On LSB and AM I couldn't get anything.

Plus the needle was swinging backwards.

So I decided to use the dipole outside and try again. This time I got a more clearer signal, and this time the needle didn't seem to swing backwards. I was able to get something on all 3 modes, although sometimes on LSB when I would key up the mic and speak, I wouldn't get anything. I would have to flip it to USB and then come back to LSB which then it seemed to work ok.

So....I need to get a second person to listen to the radio, but so far it seems to work...so thanks for the assistance, especially slprydk.

I will keep you posted on further updates.

 

[Zman]

I now own 2 of these radios and they do seem to work ok.. Not much to sing about in the power dept and it sure isnt a 449 but its a neat older radio. I like the huge meter. Sure wish there was an easier mod for the extra channels.

 

[AudioShockwav]

This is just a suggestion, but that is a old radio, and I bet the controls could use a good cleaning, you might be surprised how bad dirty controls will effect the radio.
It would be worth a run to radio shack and give them a good blast.

73
Jeff

 

[Turbo T]

I now own 2 of these radios and they do seem to work ok.. Not much to sing about in the power dept and it sure isnt a 449 but its a neat older radio. I like the huge meter. Sure wish there was an easier mod for the extra channels.

Hhmm....I read on here they are a "booty kicking radio"...I believe once you get inside and turn up the modulation.

This is just a suggestion, but that is a old radio, and I bet the controls could use a good cleaning, you might be surprised how bad dirty controls will effect the radio.
It would be worth a run to radio shack and give them a good blast.

I think you're right Jeff, I just tried doing a little DX with it using a Wilson 5k mag mount. I didn't have much luck on 38 lsb or even 39 lsb, but I did notice flipping back to AM, it got quiet....I had to wiggle the mode knob to get the AM to come back.

I'd like to know what the "MON" position on the mon-cb-pa slide switch is for?