REPAIRING AND NOT THROWING AWAY

REPAIRING AND NOT THROWING AWAY

Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and technical information about Service Modes, Circuit Diagrams, Firmware Update procedure, Disassemble procedure, Universal remote control set-up codes, Troubleshooting and more....

If you go into the profession, you will obtain or have access to a variety of tech tips databases HERE IT IS Master Electronics Repair !.

These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, checking out a tech-tips database may quickly identify your problem and solution.In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts.

Happy repairing!
Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

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..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

©2010, 2011, 2012, 2013, 2014 Frank Sharp - You do not have permission to copy photos and words from this blog, and any content may be never used it for auctions or commercial purposes, however feel free to post anything you see here with a courtesy link back, btw a link to the original post here , is mandatory.
All posts are presented here for informative, historical and educative purposes as applicable within fair use. NOTHING HERE IS FOR SALE !

Wednesday, 6 February 2019

JBL BASS 20 POWERED SUBWOOFER – CIRCUIT DIAGRAM – EXPLODED VIEW - MODIFICATIONS

JBL BASS 20 Powered Subwoofer – Circuit diagram – Exploded view - Modifications

The Bass20 powered subwoofer is part of the SCS120 or MUSIC 20 System.  User friendly “auto on” circuit. Signal sensing automatically turns the subwoofer on so you don't have to; the subwoofer is meant to be left “on” without continual use of the power switch.
Amplifier Power (RMS) . . . . . . .150 Watts
Low Frequency Woofer (2) . . . . 8 1/2"
Crossover Frequency . . . . . . . . 120Hz
Frequency Response . . . . . . . . 40Hz - 120Hz (+/-3dB)
External Dimensions (mms)
Height . . . . . . . . . . 451
Width . . . . . . . . . . .254
Depth . . . . . . . . . . .610
Weight. . . . . . . . . . 42lbs (19.1kg)
Exploded view
Circuit Diagram (Schematic)
Amplifier assemblies with serial numbers less than 11757 should be modified for safe operation. Examine amplifier as follows (serial #11756 or lower) to determine if a factory modification has taken place:
1. Unplug and remove amp assembly; (12) #8 x 3/4" screws.
2. Lift and examine the main (large) amp board, solder (green) side of the board.
3. Look for the presence of two large resistors (1k, 3 Watt or 470 ohm, 1Watt) directly underneath the two large filter caps on the opposite side of the board.
4. If these resistors are present, the unit has been modified.
5. If they are missing, the unit should be modified before future use, regardless of what the initial service concern was. To continue without modification may result in a hazardous condition.
MODIFICATION
1. Cut tie wraps to bundled wire assemblies for easier access. Circuit board does not have to be removed from heatsink.
2. R36: See drawing: cut trace connecting Q4 collector and main C1 (+) pad.
3. Create solderable surface on PCB, (on Q4 side of cut) by scraping the green mask from board with Exacto knife or similar tool.
4. Attach R36, 470 1W resistor (JBL #RS2180) to new surface and cathode side of CR1. Resistor should "stand off" from PCB; secure with RTV or epoxy if desired.
5. R41: See drawing; cut trace connecting Q1 collector and main C2 (-) pad.
6. Create solderable surface on PCB, (just above R49) by scaping the green mask from the board with Exacto knife or similar tool.
7. Attach R41, 470W 1W resistor (JBL #RS2180) to new surface and C1 (-) pad. Resistor should "stand off" from PCB; secure with RTV or epoxy if desired.
8. Retie cables with tie wraps.
9. Cut and insert two in-line fuse holders (JBL #155020A) with 4A fuses (JBL #312004); one in each positive wire leading to woofer terminal, close to the amplifier assembly.
10. Replace amp assembly in cabinet.
Posted By: FRANK at 04:41
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