Pioneer SX-434 weak Stereo Indicator Lamp

[Hardtofind]

Baby Pioneer 434. Everything is operational apart from Stereo indicator lamp. Only getting around 1 v across bulb so inserted a 3v bulb and only just glowing when in stereo. Mono switch & FM Muting working okay. Voltages across power supply and IC HA1142 appear okay. I havnt attempted to align tuner at this stage as I dont have the gear. Any thoughts ?

 

[Watthour]

Referring to the diagram below:

http://www.wwdsltd.com/files/PioneerSX-434KCUSchematic.jpg

If the lead from the indicator lamp (Pin 15 of the tuner board) is grounded, does the lamp achieve the full 5-6V? Testing that would eliminate the possibility of a supply problem through the 13V supply and the lamp dropping resistor.

 

[Hardtofind]

Thanks Watthour but that schematic looks different to my unit. Images below

 

[Watthour]

Is your unit an FV/GN type? The schematic I posted is for a KC/U type, the 120V unit typically found in North America.

Better yet, what is the board I.D. number inked on the component side? The above schematic is for the AWE-052 tuner board, but yours may be either -031 or something different.

 

[Hardtofind]

I'm in Australia so I assume the model is FV 240 vac. The board id is ANP-331-A.

 

[Hardtofind]

If the lead from the indicator lamp (Pin 15 of the tuner board) is grounded, does the lamp achieve the full 5-6V? Testing that would eliminate the possibility of a supply problem through the 13V supply and the lamp dropping resistor.[/QUOTE]

I'm back on deck with this problem. Ive tested both leads to ground & I get 13v when I'm not on any FM stations. When I tune to a station I only get 1 vdc.

 

[Watthour]

That is exactly how it should be. We can determine if the supply is adequate if Pin 15 on the tuner board is grounded (not metered) while the lamp is observed. If the supply is adequate, the lamp will illuminate.

This will help to determine if the IC is grounding the lamp when a stereo broadcast is decoded, or if the lamp or its power supply have problems.

 

[Hardtofind]

That is exactly how it should be. We can determine if the supply is adequate if Pin 15 on the tuner board is grounded (not metered) while the lamp is observed. If the supply is adequate, the lamp will illuminate.

This will help to determine if the IC is grounding the lamp when a stereo broadcast is decoded, or if the lamp or its power supply have problems.

When I ground pin 13 (thats the pin from the IC on my board not pin 15) and tune to a station there is no difference to the bulb. It is still dim.

 

[Watthour]

You should not have to tune anything. Grounding Pin 13 should turn on the Stereo lamp to full brightness regardless of what is happening in the tuner section.

If you grounded Pin 13 to a reliable chassis ground and did not turn the lamp on to full brightness, there is either a problem with the lamp itself or the lamp power supply. Since your earlier posts reported the voltage to the lamp at open-circuit condition was 13V, and that the voltage dropped to 1V when a station was tuned, I would suspect a problem with either the wrong lamp or R8 on the power supply.

 

[Hardtofind]

You should not have to tune anything. Grounding Pin 13 should turn on the Stereo lamp to full brightness regardless of what is happening in the tuner section.

If you grounded Pin 13 to a reliable chassis ground and did not turn the lamp on to full brightness, there is either a problem with the lamp itself or the lamp power supply. Since your earlier posts reported the voltage to the lamp at open-circuit condition was 13V, and that the voltage dropped to 1V when a station was tuned, I would suspect a problem with either the wrong lamp or R8 on the power supply.

Just realised that I'm using 100 ma globes as opposed to 30 ma. I have used these globes in most other applications with no issue. Trap for young players I guess. Appreciate your time and help Watthour.

 

[Watthour]

Hopefully that resolves the issue.