Need help reading RG-2 circuit diagram

[jcnash]

Hello AK,

Im in the process of restoring an RG-2 Range Expanders and one of the "upgrades" im looking to make is to increase the brightness of the power / pilot LED to match my other components

However my circuit deciphering skills seem to be lacking and I cant seem to figure out which of the following resistors I would replace with a smaller resistor to increase the brightness of the LED. Is it R124, R125 or R135 or a different one?

Appreciate any and all thoughts!

 

[markthefixer]

D25 is run off of 24v, with R125 1800 ohms of series resistance, allowing 0.015A (15 mA) to flow

D24 is run off of 27v, with R124 3900 ohms of series resistance, allowing 0.0069A (6.9 mA) to flow.

Those are old LED's, and aren't very bright, and may not like much more current than they are getting.
And with 24 or 27 volts running them, there is a huge capacity for damage with errors.
Most of the voltage is peeled off by the resistors. figure a max of 3v for the LEDs.

R125 at 1200 ohms will give you 20mA, the current that they usually specify. to do it put a 3600 ohm resistor ACROSS the R125 1800 ohm resistor to get 1200 ohms.

R124 at 1800 ohms will give you 15 mA. put a 3200 ohm resistor ACROSS the R124 3900 ohm resistor to get 1800 ohms.

 

[jcnash]

Thanks @markthefixer . I pulled out the old 1.8k ohm resistor at R125 since it looked like it was burnt to a crisp and plugged in a new beefy 2W 1k ohm resistor.

The pilot LED is now nice and bright and reading a healthy 1.9V across the LED.

Thanks very much for pointing me in the right direction.

 

[markthefixer]

<thumbs up> not yet...

 

[jcnash]

Hi @markthefixer ,

Discovered yet another issue with the RG-2 - the audio input seems to be working fine and the display starts moving when I input an audio signal via the regular input or the tape monitor input.

However there isn't any output signal being passed to the amp. Upon closer inspection, I also don't hear any relay click.

I took some voltage readings at the pins (below). Any suggestions on what I should look at further?

1: -15.26V
2: -15.26V
3: -15.26V
4: -15.26V
5: -1.9mV
6: 0V
7: -38mV
TP1: 15.25V
TP2: -15.27V

As always, really appreciate your time!

 

[jcnash]

<thumbs up> not yet...

Haha seems like it!

I assumed it was working fine when I saw the display moving…but apparently not.

 

[jcnash]

Duplicate posting error. Pls ignore.

 

[markthefixer]

Well, TP1 & TP2 show good power supply voltages.

We shall look to the non-click of the relay. That runs on the same power that lights up the power led. 24v.

when unit turns on C41 charges, C43 charges., R118 & C42 implement a time delay and storage
when unit turns off D19 keeps C43 charged, holding the relay on for a few milliseconds, anti-thump?
when unit turns off C41 discharges and D17 then drains C42
D19 keeps the rest of C43's charge

unit on
D18 reduces time delayed 15.6v on C42 to about a volt.
About a volt turns on Q30 without frying it like 15.6v would do.
D26 across the relay coil snubs the flyback surge of the collapsing magnetic field when the relay is finally turned off.

When relay NOT energized by current through Q30, the collector of Q30 is at 24 volts.
The load of the relay's current will reduce Q30's collector voltage to about 1 volt. (Vcesat in the datasheet)

 

[jcnash]

Well, TP1 & TP2 show good power supply voltages.

We shall look to the non-click of the relay. That runs on the same power that lights up the power led. 24v.

when unit turns on C41 charges, C43 charges., R118 & C42 implement a time delay and storage
when unit turns off D19 keeps C43 charged, holding the relay on for a few milliseconds, anti-thump?
when unit turns off C41 discharges and D17 then drains C42
D19 keeps the rest of C43's charge

unit on
D18 reduces time delayed 15.6v on C42 to about a volt.
About a volt turns on Q30 without frying it like 15.6v would do.
D26 across the relay coil snubs the flyback surge of the collapsing magnetic field when the relay is finally turned off.

When relay NOT energized by current through Q30, the collector of Q30 is at 24 volts.
The load of the relay's current will reduce Q30's collector voltage to about 1 volt. (Vcesat in the datasheet)

View attachment 2847887

Hi @markthefixer

After reading your post and especially "We shall look to the non-click of the relay. That runs on the same power that lights up the power led. 24v.", I had a strong feeling this problem had something to do with my previous tinkering about to increase the LED brightness.

I took a voltage reading at "G" which is the anode of the LED which should read 24V according to the schematic you highlighted, and sure enough it read ~20V - probably insufficient voltage to energize the relay.

So to test things out I pulled out the smaller resistor I had inserted and plugged in the 1.8k resistor as per the original spec and sure enough, relay clicks and the processed signal is passed to the amp. The pilot lamp is back to being dim, but I'll just live with that!

This was a strange one...I have no idea what possessed Pioneer to run the relay and the pilot lamp on the same 24V drive...but Im glad we put it to bed.

As always, thanks for your help not only in pointing me in the right direction to fix the RG-2, but also for a mini-lesson in circuit analysis!