Hi!
I've got an InterM R500 Plus amplifier which shorted due to condensation and now I'm trying to troubleshoot and fix it. The protection leds are on, channel 1 signal led is on and both clip leds are on. There is no sound.
First things first - I have only a very limited idea of what I'm doing so hoping for sincere help. I am very interested in fixing the amplifier, not because it's so worth it, but because that's my way of learning.
There were 4 resistors burned out when I opened the amp, on the output board (R501-504). So that was the obvious problem. But after changing the resistors, the problem remains.
I've measured the DC offset - channel 1 it's 69.5V, channel 2 it's around 10mV. I also measured the output of the amplifier board on channel 1 and it's the same.
Where to go from here? What and how should I measure?
Thanks!
I've got an InterM R500 Plus amplifier which shorted due to condensation and now I'm trying to troubleshoot and fix it. The protection leds are on, channel 1 signal led is on and both clip leds are on. There is no sound.
First things first - I have only a very limited idea of what I'm doing so hoping for sincere help. I am very interested in fixing the amplifier, not because it's so worth it, but because that's my way of learning.
There were 4 resistors burned out when I opened the amp, on the output board (R501-504). So that was the obvious problem. But after changing the resistors, the problem remains.
I've measured the DC offset - channel 1 it's 69.5V, channel 2 it's around 10mV. I also measured the output of the amplifier board on channel 1 and it's the same.
Where to go from here? What and how should I measure?
Thanks!
Use your DVM in the diode mode (with the amp unpowered) to check all junctions in the output transistors and drivers.
Measure from base to collector, and from ,base to emitter, in each polarity for each transistor. Look for dead shorts.
Also measure from collector to emitter on each.
First try your meter on any diode to see what it typically will read on a good junction. One way will be open/no reading.
Measure from base to collector, and from ,base to emitter, in each polarity for each transistor. Look for dead shorts.
Also measure from collector to emitter on each.
First try your meter on any diode to see what it typically will read on a good junction. One way will be open/no reading.
I checked the transistors and drivers. They measured as follows:
D113L - shorted (DIODE RL207) - This needs to be replaced.
These were shorted on all pins (DVM beeps). The readings on channel 2 with the same parts were different and no beeps.
Q 186L - BC/BE = 002; CE = 002 (TR NPN 2SC5200 TOSHIBA)
Q 176L & Q116L - BC/BE = 022; CE = 002 (TR NPN 2SC5200 TOSHIBA)
Q 117L & Q177L - BC/BE = 021; CE = 002 (TR PNP 2SA1943 TOSHIBA)
Q 187L - BC/BE = 005; CE = 002 (TR PNP 2SA1943 TOSHIBA)
These were shorted on the first and second pin, so base and collector:
Q113L - BC = 018; BE = 683; CE = 672 (KTA1659A-Y-U)
Q112L - BC = 018; BE = 698; CE = 697 (KTC4370A-Y-U)
D113L - shorted (DIODE RL207) - This needs to be replaced.
These were shorted on all pins (DVM beeps). The readings on channel 2 with the same parts were different and no beeps.
Q 186L - BC/BE = 002; CE = 002 (TR NPN 2SC5200 TOSHIBA)
Q 176L & Q116L - BC/BE = 022; CE = 002 (TR NPN 2SC5200 TOSHIBA)
Q 117L & Q177L - BC/BE = 021; CE = 002 (TR PNP 2SA1943 TOSHIBA)
Q 187L - BC/BE = 005; CE = 002 (TR PNP 2SA1943 TOSHIBA)
These were shorted on the first and second pin, so base and collector:
Q113L - BC = 018; BE = 683; CE = 672 (KTA1659A-Y-U)
Q112L - BC = 018; BE = 698; CE = 697 (KTC4370A-Y-U)
One at a time, remove those parts that tested bad, and retest each of them out of circuit, to confirm.
Continue keeping good records. Take great care to not damage the pcb.
After that, also test Q107, 108, and 109 in circuit, then remove the bad ones and retest them to confirm.
Also do the same for D106, 107, 108, and 109.
After all those (that are bad) are removed, test all the resistors from driver stage forward.
Continue keeping good records. Take great care to not damage the pcb.
After that, also test Q107, 108, and 109 in circuit, then remove the bad ones and retest them to confirm.
Also do the same for D106, 107, 108, and 109.
After all those (that are bad) are removed, test all the resistors from driver stage forward.
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Ah forgot to mention that I already tested Q107-109 and D106-109.
D106-109 all measured around 690 and didn't have shorts.
Q107 - BC = 630; BE = 161; CE = 464
Q108 - BC = 905; BE = 800; CE = 717
Q109 - BC = open; BE = 798; CE = 784
D106-109 all measured around 690 and didn't have shorts.
Q107 - BC = 630; BE = 161; CE = 464
Q108 - BC = 905; BE = 800; CE = 717
Q109 - BC = open; BE = 798; CE = 784
When you say "tested bad" then obviously the D113L is one of those. But all of the transistors like Q186L etc - does the fact that they tested bad mean that they're definitely broken?
By driver stage forward you mean? Sorry if it's a simple question, just want to clarify.
Thanks a lot for helping though!
Definitely yes, they are bad, according to what you found.
"By driver stage forward you mean? Sorry if it's a simple question, just want to clarify."
I actually meant the VAS stage, which is Q108 and Q109.
Once the resistors are checked, also go back and test all six transistors before the driver stage.
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