Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for repair

Collapse
X
 
  • Time
  • Show
Clear All
new posts

  • sam_sam_sam
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    You might have spent to much time on however this is one more item that did not end up in the landfill and you have an item should give you some years of enjoyment hopefully

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    This deck had a lot of problems, mainly with the mechanics. It was poorly assembled and several springs were missing. Poor condition of electronic and contact elements. The record switch, all VR and main potentiometer were greasy with "miracle" fluid. The previous owner must have been a hard smoker, totally everything was covered with a yellow coating.
    I measured the resistance after your 4th post, but I thought the differences were due to the damaged UPC4557.

    I spent too much time on it, but now all functions are working, it's been playing for 2 days.
    Attached Files

    Leave a comment:


  • CapLeaker
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Good that this is resolved. But I did ask about VR151 in post 4. LOL

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    VR151, 251 already changed
    The left Vu meter has started and works with the right one.

    Thank you so much everyone for your helpful words.
    This community is priceless.

    Leave a comment:


  • R_J
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    The problem with these controls in where the leads get crimped to the resistive component, that is where they get intermittent and cleaning doesn't help. If the resistance across the outside pins is 9k~30k cleaning the wiper won't fix it.

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Originally posted by budwich
    you may have more "onion skins" still (ie. faults elsewhere not allowing proper levels).... but once you get a replacement (might consider replacing both) since you indicated the other one didn't change the meter level. Further, the service manual lays out adjustments that should be done once you have the components replaced. Good luck, hopefully, you get it "whistling".
    I ordered more adjustable resistors with different values. There are also playback, record VR gain or VR sensitivities in the circuit.
    It's better to change them in pairs.

    Originally posted by redwire
    With the open (wiper) trimpots, I will clean them by dragging a piece of paper under the wiper. It acts like gentle sandpaper to clean oxide off the wiper.
    Or use a spray cleaner containing PPE like DeOxit, that works very good.
    already spryed a bit of contact pr, but resistance went up to 30k and now down to 9k. I'll do your trick with a piece of paper.

    I changed the capacitors C101, C110, C109, C121, C124, C126, C137, C141, C63 with new ones. The same in right chanel.
    I changed the drive belt and lubricated the cassette mechanism.
    Counter belt is also new.
    I was worried about weak heads, but the sound is great, clear and powerful. I'm surprised.

    Leave a comment:


  • redwire
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    With the open (wiper) trimpots, I will clean them by dragging a piece of paper under the wiper. It acts like gentle sandpaper to clean oxide off the wiper.
    Or use a spray cleaner containing PPE like DeOxit, that works very good.

    Leave a comment:


  • budwich
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    you may have more "onion skins" still (ie. faults elsewhere not allowing proper levels).... but once you get a replacement (might consider replacing both) since you indicated the other one didn't change the meter level. Further, the service manual lays out adjustments that should be done once you have the components replaced. Good luck, hopefully, you get it "whistling".

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    You both have a point. It;s the VR151 that is bad.

    When I washed the VR151, the resistance dropped to 3K. I've already ordered a new one for replacement.
    Vu meter works during play, but still weak. I will write if everything is ok after replacing the adjustable resistors.
    You guys are amazing.
    Attached Files

    Leave a comment:


  • R_J
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    VR151 must be bad, Check across the two outside pins (not the center wiper) it should read 1K. 24k suggests it is almost open.
    Does it look like this?
    Attached Files
    Last edited by R_J; 01-12-2023, 01:23 PM.

    Leave a comment:


  • budwich
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    well, not sure what to make of that. What kind of variable resistor is it? (picture?) 24K does not align with overall resistance and any "sub section" should change with the adjustment.

    Also, please indicate which pin number is connected to where in the circuit.
    Last edited by budwich; 01-12-2023, 09:02 AM.

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Originally posted by budwich
    while measuring the resistance of 2-3 adjust the vr151. Does the resistance change?
    Nothing changes, it's still 24k.

    Leave a comment:


  • budwich
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    while measuring the resistance of 2-3 adjust the vr151. Does the resistance change?

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    I measured the resistance of the main pot 2x20k R101 and R201


    pin 1 and 2
    from 19 goes down to 0

    pin 3 and 2
    from 0 goes up to 19.6

    R101,201 seems ok.

    now VR151 and VR251

    VR151

    pin 1 - 2 gnd
    from 0 goes down to 0.9

    pin 2gnd - 3
    all the time 24k!

    VR251

    pin 1 - 2 gnd
    from 0 goes down to 0.8

    pin 2gnd - 3
    from 1.1 goes down to 0

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Originally posted by Per Hansson
    No, you can only connect the ground clip to what is true ground.
    True ground is when your multimeter shows you 0.00ohm from chassis/ground clip/ground in wall socket to whatever you measure.
    Wasn't sure to witch one I can safety connect.

    Originally posted by Per Hansson
    An example: ATX PSU secondary side, provides maybe 25A on 5v line.
    Consider what will happen if you connect ground clip there?
    Sure it is only low voltage so no big explosion but it will still carry enough energy to melt traces inside the scope because you are shorting 5v to ground...
    Is ATX PSU a linear power supply or a switched-mode voltage converter?
    I think its not linear stabilizer with an isolated transformer. It's rather high-frequency switching power supply. But i might be wrong.

    Originally posted by budwich
    Does the meter adjust variable "POT" cause anything to change on either display? Verify the full resistance across the resistor along with each "portion". Compare against right and left.
    In playback mode, the VR151 potentiometer does nothing. In recording mode, the left Vu meter goes up but is weak. It shows about 30% to compare with the right one.
    Last edited by UNITRAX; 01-11-2023, 06:05 PM.

    Leave a comment:


  • Per Hansson
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Originally posted by UNITRAX
    Does this mean that after the transformer of the tape recorder I can measure everything safely?
    No, you can only connect the ground clip to what is true ground.
    True ground is when your multimeter shows you 0.00ohm from chassis/ground clip/ground in wall socket to whatever you measure.

    An example: ATX PSU secondary side, provides maybe 25A on 5v line.
    Consider what will happen if you connect ground clip there?
    Sure it is only low voltage so no big explosion but it will still carry enough energy to melt traces inside the scope because you are shorting 5v to ground...

    Leave a comment:


  • budwich
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Does the meter adjust variable "POT" cause anything to change on either display? Verify the full resistance across the resistor along with each "portion". Compare against right and left.

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Thanks.
    99% of decks have an isolated power supply. My home power supply is so old it only has 2 wires. Active and neutral without mains earth reference.

    Does this mean that after the transformer of the tape recorder I can measure everything safely?

    Leave a comment:


  • Per Hansson
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    Please watch EEVblog #279 - How NOT To Blow Up Your Oscilloscope!

    Leave a comment:


  • UNITRAX
    replied
    Re: Damaged system of the VU indicator in the JVC KD-A11 tape recorder Request for re

    I don't have an isolation transformer for the oscilloscope. That's why I asked for a hint how to connect the probe and gnd. I don't know if I measured correctly.

    I assume that the VU meter in the right channel is working properly

    0.2V/DIV
    0.1ms/DIV
    probe for C244
    I got 150mV?

    Way too much on the left channel.
    1V/DIV
    0.1ms/DIV
    probe for C144

    I'll remove the UPC4557 from the pcb and measure the resistance without the circuit.
    Attached Files
    Last edited by UNITRAX; 01-11-2023, 02:35 PM.

    Leave a comment:

Related Topics

Collapse

  • howardc64
    A1312 (27” iMac 2009-2011) A1407 (Thunderbolt Display) A1316 (Cinema Display) Display Black Screen Repair
    by howardc64
    Problem

    This is an LG edge LED lit LCD Display. The LEDs are on the bottom edge of the display. There are 2 bars (left and right) Each bar has many LEDs and a 6 pin connector. Each pin drive several LEDs thus is the highest current flow / heat junction. The weak lead free solder gradually fails with thermal expansion/contraction cycling and increases resistance. PSU will compensate up to a point, then when the current is too high, PSU just shut down the backlight causing a dark display. I have even seen one which the connector just fell off as solder points became completely detached....
    08-04-2024, 10:36 PM
  • UNITRAX
    Radio tape recorder Hitachi TRK 8010k - How to install aux in place of am band?
    by UNITRAX
    Hitachi TRK 8010k
    Is it possible to have an aux input in place of the radio on the am band range? When connecting to the tape recorder, I have additional tape noise. There is an integrated circuit HA11251 in the schematic. Which pin is the am radio output on?
    Radio tape recorder diagrams and HA11251 datasheet included...
    02-18-2023, 07:23 AM
  • RetroComputingGrotto
    IBM LTO 7 Tape Drive - Dust Sensors??
    by RetroComputingGrotto
    I have a Quantum SuperLoader robotic tape library that uses an IBM LTO 7 tape drive which is constantly complaining that it needs cleaning. If you insert a cleaning tape, it performs the clean and resets the cleaning counter to 0 hours. It should only require cleaning every 50 or so working hours but after as little as just 1 hours use it requests cleaning. We've purchased a new cleaning tape along with new LTO backup tapes but that has not resolved the problem.

    I have taken the library apart and can see no noticeable signs of dust inside. I have removed the tape drive from the...
    09-19-2024, 01:54 AM
  • triplefour
    LG 75UN8570AUD panel issue fixed with tape.
    by triplefour
    I've been seeing a lot of the new TVs (samsung and LG only i think) maybe 1-2 years old suffering from sudden panel death and have been over 50% successful bringing them at least most of the way back to functionality if not all the way, with the tape masking of the LVDS pins method.
    add this one to the list. the issue was on the left side of the panel and i ended up blocking just 3 pins on the connector that joins the two panel boards that make up the left side of the panel (it has 4 boards total) i didnt get the picture back to 100% perfect. i spent hours fiddling with which pins to block...
    07-17-2023, 10:22 PM
  • sam_sam_sam
    DVR recorder Switching power supply Failure
    by sam_sam_sam
    When I originally started with my DVR recorder it had 4 individual switching switching power supply’s that were sh*t so I bought a 7 amp 12 volt switching power supply and modified the output plug and put a four output power supply cable to match the input power supply cable inputs

    Which worked for over 14 years until a few days ago when the cameras went dark no picture anymore well it turns out now the switching power supply has stopped working altogether now so I have to troubleshoot what has happened to this power supply more later on today what I found

    This...
    05-27-2023, 03:03 AM
  • Loading...
  • No more items.
Working...