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Fisher PH-W702L boombox. Radio not working (but aux does)

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Pommaq

New Member
[SOLVED]




Hi! I created an account on this forum to try and find some tips on what could possibly be going on with it. I'll be trying my best to make this as comprehensible as possible.

I managed to pick up an old boombox (It's Casette motor is dated 1987) from a thrift store and it seems most of it functions fine, but as stated in the title, the radio doesn't work. I'm unable to test the cassettes as I dont have any to try on it. Planning to get some soon however.

And with the radio I mean Fm, Sw, Mw, and Lw are completely dead. turning the tuner knob doesnt make any change in what I suspect is background static. I have opened up the case and all components look fine. No visible corossion, cracks, leaking caps and so on.

One of the few clues I've got on what is going on are as follows:
* I can play music through it with an Aux cable, so the amplifying unit seems fine and its receiving power.
* Messing with the equalizer changes some of the hiss (I still think its background however, as it's still present when the stereo is put on Aux.)
* There is a small *pop* when I change the mode between Aux, Radio and Cassette. However No difference in noise at all when switching between Fm, Sw, Mw, and Lw.
* I have looked at the circuit board(s) with a lamp behind it, and the paths don't seem to be cracked or faulty.
* Turning the knob does turn that thing full of small metal discs (Bandpass filter?)

Edit:
* Chip on the radio tuner pcb seem fine.
* The radio tuner pcb is receiving too little power.

Ofcourse, I wasn't around when these units were built so I might just have missed a button or something. So I would approve if anyone could try and write down an instruction on how these things where supposed to function. Just incase.
I'm not really an electronics expert (Learning this as a hobby and from books, not studying it in school.) So naturally I have very basic tools. (A multimeter and soldering equipment.)


NOTE:
I've managed to repair the problem. At first the Tuner PCB wasn't receiving any power at all. This was due to a factory error on the main PCB. I mentioned what in one of my comments on this thread but I will add pieces of it here:

"However I managed to solve that as I found what would be a factory error on the main PCB (Which seems to have followed onto one of the schematics in the PDF file, PDF page 16.) According to page 17, There was supposed to be a path from S302-5 Pin 2 that should go directly to tuner radio pin +B supplying, as you said, 5.5 volts to the tuner. It was also supposed to split before reaching the tuner through D304.
I found D304 using page 16 and started to look at my circuit board to figure out where the path to CN1-B was located (as I was measuring .300 Megaohm from the switch to CN1-B, so the path was broken). The resistance being measured was from D304 to CN1-B. I started to troubleshoot where the split "clean" path towards CN1-B was supposed to be and figured out there was actually a missing component on the PCB. (Pictures here: https://imgur.com/5sIEdz0 and here is a picture of my repair: https://imgur.com/VmK4H9m). As seen on the first picture, I was pointing towards the missing component which was supposed to bridge a gap and then go straight for CN-1 B. It's said "bridge" that was non-existent on PDF page 16.)
I added a wire as seen in the second picture and that seems to have solved the no-voltage problem. I can now measure a steady 5.5 Volt between CN1 pin G and ground."

After I had fixed the connection to CN1-B I noticed that there was still a problem. The voltage reached the tuner board and passed through one 47Ohm resistor named R8 (which was measuring fine) and then the voltage just... Disappeared. So I started to look for a short-circuit. Said short-circuit was a broken electrolytic cap (Named C17) which had a steady connection of 1.4 ohms both directions, indicating it was broken. I replaced the cap and suddenly everything was working fine.
Thank you guys for helping me fix the boombox, I will definetly turn to this site again when I start another project. :)

 
Last edited:

vtech

Active Member
Majority of consumer electronics of the time suffered from intermittent mechanical switches (tarnish build up).
If nothing obvious is found, you can try using the voltage chart in the tuner section of the schematics(pg 15 of the PDF file).
At least you'd know if the front end is active/ operating? If you notice, there are several shared circuits in the radio section and if none of the operating, beside a device failure, it may not even be activated?

In general, most of the portable consumer electronics were not friendly when it come to servicing. However troubleshooting circuitry remains valid and I'd commend you in showing an interest.
 

Pommaq

New Member
Majority of consumer electronics of the time suffered from intermittent mechanical switches (tarnish build up).
If nothing obvious is found, you can try using the voltage chart in the tuner section of the schematics(pg 15 of the PDF file).
At least you'd know if the front end is active/ operating?
Thanks for the tips
Think I figured out what the voltage chart was (inserted a small piece of it in this reply, I found the correct one, right?) So far Ba4236L is measuring some really odd/small numbers when I measured it on Fm. pin 7 measured between 5-6 mV. Didn't find anything indicating whether the chart was in Volts or Millivolts, but the numbers seemed off nonetheless. I'll be measuring the rest of the chips tomorrow, I'll also test + clean the switch while I'm at it.
 

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unclejed613

Well-Known Member
Most Helpful Member
that chart is in Volts. you need to find a ground point, such as CN1 pin G. on CN1, pin B is the power for the tuner, and should be around 5.5V. that voltage originates on the amplifier board at S302-5. Q305 is the voltage regulator for that supply voltage.
 

Pommaq

New Member
that chart is in Volts. you need to find a ground point, such as CN1 pin G. on CN1, pin B is the power for the tuner, and should be around 5.5V. that voltage originates on the amplifier board at S302-5. Q305 is the voltage regulator for that supply voltage.
Alright, I looked around and at first there was no voltage going to both pin B and ground. However I managed to solve that as I found what would be a factory error on the main PCB (Which seems to have followed onto one of the schematics in the PDF file, PDF page 16.) According to page 17, There was supposed to be a path from S302-5 Pin 2 that should go directly to tuner radio pin +B supplying, as you said, 5.5 volts to the tuner. It was also supposed to split before reaching the tuner through D304.
I found D304 using page 16 and started to look at my circuit board to figure out where the path to CN1-B was located (as I was measuring .300 Megaohm from the switch to CN1-B, so the path was broken). The resistance being measured was from D304 to CN1-B. I started to troubleshoot where the split "clean" path towards CN1-B was supposed to be and figured out there was actually a missing component on the PCB. (Pictures here: https://imgur.com/5sIEdz0 and here is a picture of my repair: https://imgur.com/VmK4H9m). As seen on the first picture, I was pointing towards the missing component which was supposed to bridge a gap and then go straight for CN-1 B. It's said "bridge" that was non-existent on PDF page 16.)
I added a wire as seen in the second picture and that seems to have solved the no-voltage problem. I can now measure a steady 5.5 Volt between CN1 pin G and ground.

However, the radio is still not changing channels. but atleast now the tuner board is receiving power. I also noticed an increased amount of hum from the speakers (Perhaps now I'm picking up a signal, but am unable to change what frequency?)
I'm going to measure the voltages going towards the different legs on all the chips and will return once I figure something out.
 

Pommaq

New Member
that chart is in Volts. you need to find a ground point, such as CN1 pin G. on CN1, pin B is the power for the tuner, and should be around 5.5V. that voltage originates on the amplifier board at S302-5. Q305 is the voltage regulator for that supply voltage.
Thanks for the help! Managed to fix the problem and everything is working fine now. added what I did to my post.
 
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