Saturday, January 02, 2016

PIONEER VSX-94TXH HD AV Receiver Service mode updating the flash rom and power amplifier troubleshooting - AV receiver Repair

Contents of this article 

  • Service mode 
  • Flash Rom update 
  • Power amp failure diagnosis 

Category: AV receiver Repair  

PIONEER VSX-94TXH


How to enter the Service mode
1. Turn off MULTI-ZONE. Lower MASTER VOLUME to the minimum (---dB) and turn off the power.
2. After the power-off, press and hold down both the "ENTER" key and the "MULTI-ZONE ON/OFF" key for approximately five seconds.
How to exit the Service mode
Turning off the power or pressing the RETURN key returns to the normal mode.
Error indications when an abnormality in the amplifier system is detected
Purpose
An error message is displayed when an abnormality in the amplifier system is detected.
Description
AMP ERROR : After a failure in the amplifier block or high DC output is detected, the shutdown process starts, then the power will be shut off. Then the MCACC LED will flash. The power cannot be turned on again. If you wish to turn on the unit after a shutdown activated by DC detection, enter DC detection cancellation mode, by proceeding with the steps described in "How to enter release mode" below.
Press and hold " (DOWN)" and "MULTI-ZONE ON/OFF" keys on the front panel simultaneously for 2 seconds in standby mode.
Before the Power Amp Block is removed
Procedure
Before the Power Amp Block is removed, discharge C4209 and C4210 on the TRANS 2-1 Assy, as indicated below.
If you don't, the IC protectors (IC4261 and IC4262) on the VH TR Assy may be open, and DC voltage may be generated at the power amplifier output, which will result in "AMP ERR."
1 Unplug the AC code.
2 Discharge C4209 and C4210 on the TRANS 2-1 Assy.
Note: For discharging, use a load of 100Ω, 3W or more, to protect the IC protectors. Do NOT discharge instantly by short-circuiting.
3 Check that the voltage between the electrodes of each C4209 and C4210 is 1V or less.
4 Mount the Power Amp Block.
HOW TO UPDATE THE FLASH ROMS FOR VARIOUS MICROCOMPUTERS
Do NOT disconnect the AC power cords of this unit nor the PC.
Procedures
1. Turn off the power to this unit by setting the main volume level to "---dB" and Multi-Zone to "OFF".
2. Connect the 232C cross cable and the PC, as indicated in "Connections".
3. Simultaneously press and hold the ENTER and MULTI ZONE ON/OFF keys for about 5 seconds.
4. Turn the power ON at CONFIDENTIAL PANEL mode.
5. (HDMI microcomputer)
Press DOWN key and select “HDMI DL [START]” display.
Press ENTER key and set to “HDMI DL [GO ON]”. (MAIN microcomputer)
Press DOWN key and select “MAIN DL [START]” display.
Press ENTER key and set to “MAIN DL [GO ON]”. (DSP microcomputer)
Press DOWN key and select “DSPM DL [START]” display.
Press ENTER key and set to “DSPM DL [GO ON]”. (EVENT microcomputer)
Press DOWN key and select “EVNT DL [START]” display.
Press ENTER key and set to “EVNT DL [GO ON]”.
6. Double-click on "ufu.exe".
7. Check that "Full" is selected in MODE SELECT.
8. Select the firm ware file with "mot" extension.
9. Select the communication speed.
# Basic speed: 19200
# Data transfer speed: 57600
10. Click on "START" button.
11. "Completed" is displayed in the"ufu.exe" window.
12. Disconnect then reconnect the AC power cord of the unit. If the unit is not reset, retry from Step 2.
13. Check the version.
Following the procedures described in
"Version indication" in "SERVICE MODE," check that the version has been changed to a new one.
FAILURE DIAGNOSIS OF THE POWER AMP BLOCK
If "AMP ERR" flashes on the FL display immediately after the power is turned on, then the unit is shut down, the power amplifier block is damaged, and DC voltage is output. In this case, either or both of the current and voltage amplifier block(s) is(are) damaged. Herein is described how to diagnose which block is in failure. Most cases of damage in the power amplifier block are damage on the power transistor caused by excess power consumption, such as short-circuiting of the speaker terminals and use of low-impedance speakers that are not guaranteed. The failure diagnosis is therefore conducted on the current amplifier block first, then on the voltage amplifier block.
Notes:
# During diagnosis of the amplifier block with the power on, if you touch a high-impedance circuit (in particular, both ends of 100-ohm base resistance of the power transistor) with the probe of an oscilloscope or a tester, the circuit may be damaged by oscillation of an oscilloscope or a tester.
# While a failure diagnosis is being conducted with the power on, do NOT touch parts other than the power, input, and output blocks.
# Only the points with CP (check point) marks in the schematic diagram can be diagnosed while the power is on.
1. Damage on the current amplifier block Check of the power transistor and collector resistance of each channel, using a tester
Tips:
In most cases where the current amplifier block is damaged by an excess power consumption of the power transistor, damage is caused by short-circuiting between the collector and emitter. The collector resistor is open because of large collector current. In this case, the channel in failure can be identified by checking on which channel the resistance between C and E of the power transistor is 0 Ω (some hundreds of ohms or less) and the resistor of collector resistor is ∞ Ω. As a damage scar appears on the surface of the part when the collector resistor is open, you can also check it by visual inspection.
Note:
Even if the result of the measurement of resistance with the tester shows that the power transistor is not short-circuited, that power transistor may be damaged if the paired push-pull power transistor has been damaged. Therefore, it is recommended to replace both parts when either needs to be replaced.
2. Damage on the voltage amplifier block Check of the base resistance (100 Ω) and Power supply (±VH) resistor (4.7 Ω) of each channel, using a tester
Tips:
In most cases, the voltage amplifier block is damaged by oscillation generated by a special load connection, a largeamplitude output at higher frequencies out of the audible range, or an influence of damage on the current amplifier block (power transistors). In many cases, the base resistance (100 Ω) is damaged. It is necessary to check each part of the voltage amplifier block, as damage may have been extended to other parts.
In most cases, the resistors are open/damaged, or the transistors or diodes are short-circuited/damaged.
# The resistors must not be open (the resistance must not be higher than the indicated value).
# The terminals of transistors or diodes must not be shortcircuited (the resistance must not be extremely low). (If the resistance is low but you are not sure if it is extremely low, compare the value with that of the normal channel.)
If the voltage amplifier block is damaged, Power supply (±VH) resistor (4.7 Ω) may also be damaged.
3. Other damage
Check of the bias protection diodes
Tips:
If the power amplifier is damaged, the bias protection diodes may be deteriorated or open. For a channel that has been diagnosed to be in failure, the Vf (forward descending voltage) of the four diodes must be checked to confirm that they are not deteriorated or open, using a tester, after repair of the amplifier. If these diodes are deteriorated, its distortion/frequency characteristics may be affected. If these diodes are open, the scale of damage on the power transistors may be extended if any abnormality is generated in the amplifier next time.