I am a newbie here and am trying to troubleshoot a Sanyo RP-1350 with six transistors. Vintage 79-80 I think. It runs 3V. I can inject a signal into the base of all transistors and it does come to the speaker. The first transistor is weak but it does go all the way through. The radio does not receive any stations at all. When I got it one of the antenna wires was broken. I repositioned it to the base of the first transistor. I apologize I don't have a schematic but that seemed appropriate. There were already two leads going to the tuning capacitor.
I have searched and cannot find a schematic for this model. I am thinking of taking out some of the components at the front end of the circuit and testing them but worried about damage. At the Collector of the first transistor I did measure 2.6V leaving it and I think .7 v going in the base. I am puzzled. I know the radio is not worth much but I am using it to try to learn.

 

Welcome to AAC!

Before you do anymore dismantling, take sharp photos of both sides of the circuit board and post them here.
We need to make sure that the broken wires go back where they belong.

 

I apologize I don't have a schematic...

This should be close.

 

I am a newbie here and am trying to troubleshoot a Sanyo RP-1350 with six transistors. Vintage 79-80 I think. It runs 3V. I can inject a signal into the base of all transistors and it does come to the speaker. The first transistor is weak but it does go all the way through. The radio does not receive any stations at all. When I got it one of the antenna wires was broken. I repositioned it to the base of the first transistor. I apologize I don't have a schematic but that seemed appropriate. There were already two leads going to the tuning capacitor.
I have searched and cannot find a schematic for this model. I am thinking of taking out some of the components at the front end of the circuit and testing them but worried about damage. At the Collector of the first transistor I did measure 2.6V leaving it and I think .7 v going in the base. I am puzzled. I know the radio is not worth much but I am using it to try to learn.

Sanyo made many different AM radios over the years but I can't find a manual for the RP-1350. Early AM transistor circuits were all very similar. Here is the manual for an earlier version of a Sanyo 3V portable AM radio, the RP-1250. It has a slightly different physical configuration but the circuit diagram should be very similar to the RP-1350. You should be able to use it as a guideline.

 

I am a newbie here and am trying to troubleshoot a Sanyo RP-1350 with six transistors. Vintage 79-80 I think. It runs 3V. I can inject a signal into the base of all transistors and it does come to the speaker. The first transistor is weak but it does go all the way through. The radio does not receive any stations at all. When I got it one of the antenna wires was broken. I repositioned it to the base of the first transistor. I apologize I don't have a schematic but that seemed appropriate. There were already two leads going to the tuning capacitor.
I have searched and cannot find a schematic for this model. I am thinking of taking out some of the components at the front end of the circuit and testing them but worried about damage. At the Collector of the first transistor I did measure 2.6V leaving it and I think .7 v going in the base. I am puzzled. I know the radio is not worth much but I am using it to try to learn.

attached are some photos

 

This should be close.

View attachment 317070

 

Thank you very much for this. I found this one in my search but not sure. This is a much clearer copy. I can push the trace signal to the speaker even from the base of the very first transistor. And especially good from the volume control pot. So I am certain the problem is not in the amplifier section but somewhere up front in the RF/IF areas.

 

Sanyo made many different AM radios over the years but I can't find a manual for the RP-1350. Early AM transistor circuits were all very similar. Here is the manual for an earlier version of a Sanyo 3V portable AM radio, the RP-1250. It has a slightly different physical configuration but the circuit diagram should be very similar to the RP-1350. You should be able to use it as a guideline.

Thank you so much, this should be a great help to me. At least the circuits are probably very close. Having the full manual to read will also be helpful. I really do appreciate this. The membership of this forum is FANTASTIC!

 

Thank you very much for this. I found this one in my search but not sure. This is a much clearer copy. I can push the trace signal to the speaker even from the base of the very first transistor. And especially good from the volume control pot. So I am certain the problem is not in the amplifier section but somewhere up front in the RF/IF areas.

Depends on the nature of the trace signal. An AF signal will certainly allow you to test the AF section of the radio.
The first transistor is an RF amp/local oscillator/mixer circuit. The next two stages are IF amplifiers.

You need an RF spectrum analyzer to check that the local oscillator is working at the proper frequency.
Then you need an RF generator to test the IF stages.

The typical local oscillator frequency is 455kHz + incoming RF. However, the IF could be different from 455kHz.

 

Let us assume that the IF is 455kHz.
Let us assume that the MW band ranges from 500kHz to 1600kHz.
The local oscillator has to be tunable from 955kHz to 2055kHz (assuming that the IF is the difference frequency).
If you had a SW radio that can receive 1MHz to 2MHz, you might be able to pick up the local oscillator signal.

 

Thank you so much, this should be a great help to me. At least the circuits are probably very close. Having the full manual to read will also be helpful. I really do appreciate this. The membership of this forum is FANTASTIC!

You are welcome. The transistor voltages listed below the schematic should give you a good indication of where to start.

 

You are welcome. The transistor voltages listed below the schematic should give you a good indication of where to start.

I have been studying it and plan to check tomorrow

 

I have been studying it and plan to check tomorrow

On the AM radios, the IF transformers are done in this order//

RED local oscillator
YELLOW second IF
BLACK last IF.

The RED one will alter the tuning dial frequency , this is critical.

 

On the AM radios, the IF transformers are done in this order//

RED local oscillator
YELLOW second IF
BLACK last IF.

The RED one will alter the tuning dial frequency , this is critical.

Thanks it seems like the oscillator is not working. I am checking some voltages this morning on the Q1 transistor.

 

I have been studying it and plan to check tomorrow

The transistors are obsolete but any modern general purpose NPN transistor like 2N3904 will work as a replacement for all except Q703 which is PNP - use 2N3906 for that one.

 

Okay. Thanks again. I had .702v on the base. 100mv on the emitter and then 2.9v on collector. I am checking a capacitor and a couple resisters then will look closer at the transister.

 

The transistors are obsolete but any modern general purpose NPN transistor like 2N3904 will work as a replacement for all except Q703 which is PNP - use 2N3906 for that one.

The Q101 transistor I pulled was a 9011 BC G. Have no idea if that's the right one. It does check to be an NPN and appears good in my LCR7 tester. I might replace it with a new one 2N3904 just to eliminate it as a potential problem. Two resisters I checked matched the circuit diagram and checked good. I am still hunting down other component issues. I am wondering if the tuning capacitor is not working or if the antenna connection to the tuning capacitor is bad.

 

Let us assume that the IF is 455kHz.
Let us assume that the MW band ranges from 500kHz to 1600kHz.
The local oscillator has to be tunable from 955kHz to 2055kHz (assuming that the IF is the difference frequency).
If you had a SW radio that can receive 1MHz to 2MHz, you might be able to pick up the local oscillator signal.

Thank you for your advice. I may have a SW radio I can borrow.

 

The transistors are obsolete but any modern general purpose NPN transistor like 2N3904 will work as a replacement for all except Q703 which is PNP - use 2N3906 for that one.

Pleased to report that I replaced the 9011 transistor with the 2N3904 and I am now receiving AM stations all the way through the speaker. The sound is weak so I will check some of the other transistors. But yes without this advice I would not have got it working so far. Thanks a bunch. Everyone here is fantastic!

 

Pleased to report that I replaced the 9011 transistor with the 2N3904 and I am now receiving AM stations all the way through the speaker. The sound is weak so I will check some of the other transistors. But yes without this advice I would not have got it working so far. Thanks a bunch. Everyone here is fantastic!

If the signal is weak try adjusting the Yellow IF transformer, ( use a plastic or wooden screwdriver) and then the Black one to see if the signal increases, you can use an external amplifier across the outer terminals of the volume volume control, and if it's better, then you can see what the audio amplifier is like on the Sanyo.