Fixing a legend.....
- Thread starter blu_fuz
- Start date
Athlete's foot odor or save the Panasonic...blu_fuz said:....and my big toe is touching the outlet face plate screw to ground me out so I don't zap a static shock into the Panasonic.
Absolutely save that Panasonic!
Seriously? Just get yourself a grounding wrist (ankle) strap. They are probably $3 on eBay and don't require you to perform twister style acrobatics to protect your BOOMBOX. Also would be good to invest in a grounded rubber work mat too.
baddboybill
Boomus Fidelis
Just use a condom Joe and no need to worry about shooting a load..... Of current. OK JK
Bad Boy Bill
OK JK Bad Boy Bill
BoomboxLover48
Boomus Fidelis
baddboybill
Boomus Fidelis
My prediction is in two weeks time we will see this RX5350 all working! 
I hope so.. Be nice to hear one in person
Bad Boy Bill
I hope so.. Be nice to hear one in person
Bad Boy Bill
OK, I added pictures and test results: https://boomboxery.com/forum/index.php/topic/19914-fixing-a-legend/?p=255104
I'm getting a headache flipping back/forth as this is starting to get convoluted. Also, because you admittedly didn't have all settings in the prescribed positions prior to taking measurements, it makes all measurements suspect and untrustworthy since the settings WILL definitely affect the readings. I spent about 1/2 hour to stitch the two pages since I it was too difficult to follow the two parts unless they were continguous (I don't have a printer available right now).
I'm going to ask that you retest after carefully checking all settings are correct first. Here's why:
You indicated that the collector of Q411 is reading 9.0 volts when it should be reading "0". However, the schematic shows that the C lead is tethered to and runs through S15, which then goes to S3-3. See where it goes next? That's right, GROUND. So unless there is a break in the circuit, any voltage at that location should be shorted to ground and result in..... yep, "0" volts. So several things here..... either the switches are not in the proper positions, or the switches are internally open, or the traces/jumpers are broken. Now, if the switches are not in the proper positions, then no amount of troubleshooting will help since I need to presume that the readings you are getting are abnormal for the prescribed settings. Whenever I feel like I can't trust the readings, then I stop diagnosing since it's really a waste of time because the analysis makes certain presumptions of the circuit and the diagram represents a dynamic circuit and the specifications are only accurate as long as the required settings are adhered to.
Now I do know that it's not easy to get all the switches into the proper position when the boombox is apart. The legends are all on the case (which is off) and the board is dangling and the switches are all easy to disturb, especially if they are flip levers and you are actively flipping the board. Unfortunately, it's really a necessity. Sorry Joe, I don't envy the job ahead of you, but better YOU than ME, haha.
BTW, looks like IC402 "might" be bad. I looked at the internal block diagram for that IC and pins 4 (supply) and 3 are internally separated by some circuits. However, you are getting almost the exact same voltage on 3/4 which almost seems like it's internally shorted. I think you ought to consider changing it but then again, that is the tape preamp and you did not have it in tape mode so I'm not 100% but it certainly warrants further investigation. If it was me and I had that IC lying around, I would swap it in a heartbeat.
Also, you indicated Q407 B is getting 0 volts. It needs at least 0.7 in order to turn on. If you follow along, you'll find that the circuit goes from B/Q407 through R458 (100k), then R468 (100), then switch 3-4, then R441 (100), then C/Q206. As you can see, C of Q206 is reading 7.4V which you indicated is correct. Well, if that is the case, why then does B/Q407 not have any voltage? Again, either there is a broken connection, one of the resistors is blown, OR SW 3/4 is in the IMPROPER position again. Now I did spend about 20-30 minutes tracing these (see 3rd paragraph above) presuming that the readings were incorrect and that conclusion can only be accurate if the switches are in the proper position.
For these reasons, I'm gonna stop now. Maybe when you got more time without distractions, you can slowly make sure everything is correct before taking measurements. I know it's not easy so you'll want to do it right or else the prospect of continous retesting looms perpetually.....
I'm going to ask that you retest after carefully checking all settings are correct first. Here's why:
You indicated that the collector of Q411 is reading 9.0 volts when it should be reading "0". However, the schematic shows that the C lead is tethered to and runs through S15, which then goes to S3-3. See where it goes next? That's right, GROUND. So unless there is a break in the circuit, any voltage at that location should be shorted to ground and result in..... yep, "0" volts. So several things here..... either the switches are not in the proper positions, or the switches are internally open, or the traces/jumpers are broken. Now, if the switches are not in the proper positions, then no amount of troubleshooting will help since I need to presume that the readings you are getting are abnormal for the prescribed settings. Whenever I feel like I can't trust the readings, then I stop diagnosing since it's really a waste of time because the analysis makes certain presumptions of the circuit and the diagram represents a dynamic circuit and the specifications are only accurate as long as the required settings are adhered to.
Now I do know that it's not easy to get all the switches into the proper position when the boombox is apart. The legends are all on the case (which is off) and the board is dangling and the switches are all easy to disturb, especially if they are flip levers and you are actively flipping the board. Unfortunately, it's really a necessity. Sorry Joe, I don't envy the job ahead of you, but better YOU than ME, haha.
BTW, looks like IC402 "might" be bad. I looked at the internal block diagram for that IC and pins 4 (supply) and 3 are internally separated by some circuits. However, you are getting almost the exact same voltage on 3/4 which almost seems like it's internally shorted. I think you ought to consider changing it but then again, that is the tape preamp and you did not have it in tape mode so I'm not 100% but it certainly warrants further investigation. If it was me and I had that IC lying around, I would swap it in a heartbeat.
Also, you indicated Q407 B is getting 0 volts. It needs at least 0.7 in order to turn on. If you follow along, you'll find that the circuit goes from B/Q407 through R458 (100k), then R468 (100), then switch 3-4, then R441 (100), then C/Q206. As you can see, C of Q206 is reading 7.4V which you indicated is correct. Well, if that is the case, why then does B/Q407 not have any voltage? Again, either there is a broken connection, one of the resistors is blown, OR SW 3/4 is in the IMPROPER position again. Now I did spend about 20-30 minutes tracing these (see 3rd paragraph above) presuming that the readings were incorrect and that conclusion can only be accurate if the switches are in the proper position.
For these reasons, I'm gonna stop now. Maybe when you got more time without distractions, you can slowly make sure everything is correct before taking measurements. I know it's not easy so you'll want to do it right or else the prospect of continous retesting looms perpetually.....
No, the power supply thing can be accounted for in the readings, especially those that are tethered to the power rails. Most boomboxes, especially quality ones will have built in voltage regulators on circuits where voltage settings are critical. The regulators don't regulate the entire box, just those particular ones. There's probably 6-10 regulators in the M70/M90 for various circuits.
The switch settings, however are critical because they turn parts of circuits on or off.
Anyhow, I just want to make sure any advice or suggestions I give are meaningful and accurate. You ever heard the term gobbledygook? It basically means garbage in, garbage out. Back in the early days of computing, instructors remind us that computers are stupid and because they only process what you feed it, and don't interpret what you meant to feed it. So during programming, if you fed it bad code, you would get bad result. The computer doesn't care -- it processes anything. In this case, any analysis or conclusion would only be as good as the data used to arrive at the conclusion. Wrong data means wrong conclusion.
The switch settings, however are critical because they turn parts of circuits on or off.
Anyhow, I just want to make sure any advice or suggestions I give are meaningful and accurate. You ever heard the term gobbledygook? It basically means garbage in, garbage out. Back in the early days of computing, instructors remind us that computers are stupid and because they only process what you feed it, and don't interpret what you meant to feed it. So during programming, if you fed it bad code, you would get bad result. The computer doesn't care -- it processes anything. In this case, any analysis or conclusion would only be as good as the data used to arrive at the conclusion. Wrong data means wrong conclusion.
You'll also note that I did advise (approx 6 posts down) on previous page to make sure settings are correct before taking measurements or results will be off.
I was able to go through and get my V readings with all the correct settings. The ONLY setting I didn't have correct was the PHONO/LINE IN switch was set to line in and it needs to be set to phono! LOL. So close!
I also tried to get the REC and FM voltage readings. The REC settings with the tape in REC mode all said 0v and probably have nothing to do with the problems with my Panasonic. The FM voltage readings were consistant no matter if I was in FM/AM/SW/tape/radio/line in/ made no difference and there were only 2 readings that are fishy for the FM voltages. Probably not significant for what is happening with the buzzing noise either, but I did try and test what I could.
Schematic with "check" marks at normal component readings and "arrows" calling out abnormal readings. Abnormal readings noted below in RED and also marked on schematic.
View attachment 5350 Schematic.pdf
Board diagram (easier to read) with all component readings.
View attachment 5350 Board Diagram.pdf
Q407
C) 0.1v reading = 3.04v
B) 0.7v reading = 0v
E) 0.1v reading = 0v
IC402
1) 1.4v reading = 0.76v
2) 0.9v reading = 0.16v
3) 3v reading = 8.48v
4) 7.7v reading = 8.49v
5) 0v reading = 0v
6) 3.1v reading = 4.13v
7) 0.9v reading = 0.91v
8) 1.4v reading = 1.48v
IC101 / IC201 (same readings for both components within .01)
1) 4.5v reading = 4.64v
2) 4.5v reading = 4.62v
3) 4.5v reading = 4.52v
4) 4.6v reading = 4.64v
5) 4.5v reading = 4.57v
6) 4.5v reading = 4.62v
7) 4.6v reading = 4.71v
8) 0v reading = 0v
9) 0v reading = 0v
10) 2.2v reading = 2.1v
11) 4.7v reading = 4.78v
12) 2.2v reading = 2.1v
13) 2.2v reading = 2.12v
14) 2.2v reading = 5.25v
15) 2.1v reading = 5.13v
16) 9.1v reading = 9.29v
IC403 [FM]
1) 1.3v reading = 1.34v
2) 1.3v reading = 1.34v
3) 1.8v reading = 1.84v
4) 8v reading = 8.35v
5) 1.6v reading = 1.51v
6) 4.4v reading = 1.09v
7) 1.8v reading = 2.09v
8) 4.4v reading = 1.09v
9) 0v reading = 0v
10) 6v reading = 6.31v
11) 1.8v reading = 1.82v
12) 0.3v reading = 0.24v
13) 1.8v reading = 1.82v
14) 1.8v reading = 1.83v
15) 1.6v reading = 1.64v
16) 1.8v reading = 1.83v
Q109 / Q209
C) 0v reading = 0.4v / 0.47v
B) 0.7v reading = 0v
E) 0v reading = 0v
Q108 / Q208
C) 0v reading = 0.28v / 0.34v
B) 0.7v reading = -0.56v / -0.54v
E) 0v reading = 0v
Q408 (forgot to mark the readings on the schematic)
C) 8.4v reading = -0.56v
B) 7.6v reading = 9.02v
E) 8.4v reading = 9.02v
Q411
C) 0v reading = 9.09v
B) 0.7v reading = 0v
E) 0v reading = 0v
I also tried to get the REC and FM voltage readings. The REC settings with the tape in REC mode all said 0v and probably have nothing to do with the problems with my Panasonic. The FM voltage readings were consistant no matter if I was in FM/AM/SW/tape/radio/line in/ made no difference and there were only 2 readings that are fishy for the FM voltages. Probably not significant for what is happening with the buzzing noise either, but I did try and test what I could.
Schematic with "check" marks at normal component readings and "arrows" calling out abnormal readings. Abnormal readings noted below in RED and also marked on schematic.
View attachment 5350 Schematic.pdf
Board diagram (easier to read) with all component readings.
View attachment 5350 Board Diagram.pdf
Q407
C) 0.1v reading = 3.04v
B) 0.7v reading = 0v
E) 0.1v reading = 0v
IC402
1) 1.4v reading = 0.76v
2) 0.9v reading = 0.16v
3) 3v reading = 8.48v
4) 7.7v reading = 8.49v
5) 0v reading = 0v
6) 3.1v reading = 4.13v
7) 0.9v reading = 0.91v
8) 1.4v reading = 1.48v
IC101 / IC201 (same readings for both components within .01)
1) 4.5v reading = 4.64v
2) 4.5v reading = 4.62v
3) 4.5v reading = 4.52v
4) 4.6v reading = 4.64v
5) 4.5v reading = 4.57v
6) 4.5v reading = 4.62v
7) 4.6v reading = 4.71v
8) 0v reading = 0v
9) 0v reading = 0v
10) 2.2v reading = 2.1v
11) 4.7v reading = 4.78v
12) 2.2v reading = 2.1v
13) 2.2v reading = 2.12v
14) 2.2v reading = 5.25v
15) 2.1v reading = 5.13v
16) 9.1v reading = 9.29v
IC403 [FM]
1) 1.3v reading = 1.34v
2) 1.3v reading = 1.34v
3) 1.8v reading = 1.84v
4) 8v reading = 8.35v
5) 1.6v reading = 1.51v
6) 4.4v reading = 1.09v
7) 1.8v reading = 2.09v
8) 4.4v reading = 1.09v
9) 0v reading = 0v
10) 6v reading = 6.31v
11) 1.8v reading = 1.82v
12) 0.3v reading = 0.24v
13) 1.8v reading = 1.82v
14) 1.8v reading = 1.83v
15) 1.6v reading = 1.64v
16) 1.8v reading = 1.83v
Q109 / Q209
C) 0v reading = 0.4v / 0.47v
B) 0.7v reading = 0v
E) 0v reading = 0v
Q108 / Q208
C) 0v reading = 0.28v / 0.34v
B) 0.7v reading = -0.56v / -0.54v
E) 0v reading = 0v
Q408 (forgot to mark the readings on the schematic)
C) 8.4v reading = -0.56v
B) 7.6v reading = 9.02v
E) 8.4v reading = 9.02v
Q411
C) 0v reading = 9.09v
B) 0.7v reading = 0v
E) 0v reading = 0v
Well, Joe since you are so eager to continue fussing with this, here are some things for you to do:
IC403 (BA1355). This is the stereo decoder. Hopefully it is ok because it might be a little hard to find.
1) Check value of R420 = 4.7K Ω
Q407: Check the following:
1) Resistance, R458 (lead opposite Q407-B) to S3-4 (pin 1 & 4), confirm = 100Ω
2) Resistance, S3-4 (pin 1 & 4) to R441 (both pins), confirm R=0Ω & R=100Ω
3) Resistance, R441 (both leads) to Q206-C, confirm R=0Ω & R=100Ω
IC402: I would change it if I were you.
IC101, IC201: Dolby NE649N. This is the dolby chip. They might be bad. I have seen dolby chips go bad a lot. However, you are getting the exact same readings on both chips. Did they both fail exactly the same way? It's possible but not that likely. More likely is that they are compensating for the hum present in your audio, without which they voltages might read more normal. Also, is the dolby setting on/off? Might make a difference. I would leave those for now until you've corrected all other discrepencies first.
Q408: You marked it as if there was some anomoly in the readings. Yet, I don't see any test voltages marked.
Q411: Check:
1) Voltage, @ R464 (both sides)
2) Resistance, R464 (both sides) to D103/D203 (the lead common to both diodes).
R465: Check:
1) Resistance value
2) Continuity of the traces from the pins of R465 to at least 1 or 2 trace pads further up/down stream.
IC403 (BA1355). This is the stereo decoder. Hopefully it is ok because it might be a little hard to find.
1) Check value of R420 = 4.7K Ω
Q407: Check the following:
1) Resistance, R458 (lead opposite Q407-B) to S3-4 (pin 1 & 4), confirm = 100Ω
2) Resistance, S3-4 (pin 1 & 4) to R441 (both pins), confirm R=0Ω & R=100Ω
3) Resistance, R441 (both leads) to Q206-C, confirm R=0Ω & R=100Ω
IC402: I would change it if I were you.
IC101, IC201: Dolby NE649N. This is the dolby chip. They might be bad. I have seen dolby chips go bad a lot. However, you are getting the exact same readings on both chips. Did they both fail exactly the same way? It's possible but not that likely. More likely is that they are compensating for the hum present in your audio, without which they voltages might read more normal. Also, is the dolby setting on/off? Might make a difference. I would leave those for now until you've corrected all other discrepencies first.
Q408: You marked it as if there was some anomoly in the readings. Yet, I don't see any test voltages marked.
Q411: Check:
1) Voltage, @ R464 (both sides)
2) Resistance, R464 (both sides) to D103/D203 (the lead common to both diodes).
R465: Check:
1) Resistance value
2) Continuity of the traces from the pins of R465 to at least 1 or 2 trace pads further up/down stream.
See Q408 post above. I forgot to write on the schematic before it was scanned but I have the voltages listed above.
I will probably start with the IC402 swap and fire it up. One step at a time and will follow the steps you noted.
Also, I do have the replacement IC101 and IC201 chips here if needed as well.
I will probably start with the IC402 swap and fire it up. One step at a time and will follow the steps you noted.
Also, I do have the replacement IC101 and IC201 chips here if needed as well.
BTW I forgot to mention. Your boombox is strictly a DC powered boombox. The mains power supply converts the AC input into DC. Ground should be the negative rail (-), or "0" volts.
What this means is that a good ground should be same as negative rail and at "0" volts potential.
I need to make this distinction because many AC powered devices such as home stereo receivers have dual power supplies where:
(-) --- (ground) --- (+). Therefore, if you measure from (-) to (ground), you will get from (-) to (0) volts. If you measure from ground to (+), you will get from (0) to (+) volts. IF you measure from (-) to (+), you will get the combined potential difference between the negative rail PLUS the positive rail. So if your dual power supply has -50, +90 volts, and you measured from the negative rail to the positive rail, you will measure +140 volts or if your supply is +/-12V, then the potential between the + and - rails is 24v.
What does all this mean for YOU?
Any (-) readings means you've measured incorrectly, or measured with the (-) lead at a location HIGHER than ground potential. OR it could mean that your ground is actually not ground, but a potential higher than ground.
For example, your BLACK probe is clipped to a location with .56volts. Your RED probe is probed at a location of "0" volts. The reading will measure -.56volts.
This can be significant because it can mean that your ground is not actually at "true" ground potential. Remember I told you that a ground loop will cause hum? You need to find a good negative anchor point and check your grounds to make sure they are actually grounds. You can do that by measuring continuity between the "known" good ground (with power off of course) and checking all the ground points. OR you can check live using voltmeter setting, with BLACK probe at known good ground location, and probe RED used to check ground locations. You should read "0" volts. If you are getting 1/2 volts, it means that THAT location is NOT properly grounded and current is taking a circuitous path back to neg source.
What this means is that a good ground should be same as negative rail and at "0" volts potential.
I need to make this distinction because many AC powered devices such as home stereo receivers have dual power supplies where:
(-) --- (ground) --- (+). Therefore, if you measure from (-) to (ground), you will get from (-) to (0) volts. If you measure from ground to (+), you will get from (0) to (+) volts. IF you measure from (-) to (+), you will get the combined potential difference between the negative rail PLUS the positive rail. So if your dual power supply has -50, +90 volts, and you measured from the negative rail to the positive rail, you will measure +140 volts or if your supply is +/-12V, then the potential between the + and - rails is 24v.
What does all this mean for YOU?
Any (-) readings means you've measured incorrectly, or measured with the (-) lead at a location HIGHER than ground potential. OR it could mean that your ground is actually not ground, but a potential higher than ground.
For example, your BLACK probe is clipped to a location with .56volts. Your RED probe is probed at a location of "0" volts. The reading will measure -.56volts.
This can be significant because it can mean that your ground is not actually at "true" ground potential. Remember I told you that a ground loop will cause hum? You need to find a good negative anchor point and check your grounds to make sure they are actually grounds. You can do that by measuring continuity between the "known" good ground (with power off of course) and checking all the ground points. OR you can check live using voltmeter setting, with BLACK probe at known good ground location, and probe RED used to check ground locations. You should read "0" volts. If you are getting 1/2 volts, it means that THAT location is NOT properly grounded and current is taking a circuitous path back to neg source.