Hi,
Would anyone have an electronic copy of the service manual, including schematic, for the Gemini GXA 1600 amp? I'm currently using the manual for the XPB 750/1600, which is very similar but must be different.
The main issue is a fault with the left channel, which is dead but for its yellow "Protect" LED flickering and the sound of a relay clicking on and off inside the amp. The left-channel LED flickers without any audio input or output connected but the flickers appear to increase in frequency as the left volume control is increased. Perhaps this is of no real significance but including it as it's what I observed. Despite the relay clicking on and off intermittently (less frequent than flickering) the left-speaker channel is completely silent.
I suspect a thermistor may be at fault, but that is just my initial suspicion. The channel failed after switch on with a low volume. It was connected to a single Peavey two-way speaker at the time, I'm told. Hoping none of the OT have failed but not ruling them out. Any experience, hints, tips, problem-pointers with repairing these amps would be appreciated.
Cheers
Would anyone have an electronic copy of the service manual, including schematic, for the Gemini GXA 1600 amp? I'm currently using the manual for the XPB 750/1600, which is very similar but must be different.
The main issue is a fault with the left channel, which is dead but for its yellow "Protect" LED flickering and the sound of a relay clicking on and off inside the amp. The left-channel LED flickers without any audio input or output connected but the flickers appear to increase in frequency as the left volume control is increased. Perhaps this is of no real significance but including it as it's what I observed. Despite the relay clicking on and off intermittently (less frequent than flickering) the left-speaker channel is completely silent.
I suspect a thermistor may be at fault, but that is just my initial suspicion. The channel failed after switch on with a low volume. It was connected to a single Peavey two-way speaker at the time, I'm told. Hoping none of the OT have failed but not ruling them out. Any experience, hints, tips, problem-pointers with repairing these amps would be appreciated.
Cheers
the service manual you have covers both models the major difference is in the number of output pairs.
first thing i'd do is see if there's any dc on the output + of that channel ahead of the relay of course.
do you have a dim bulb tester?
first thing i'd do is see if there's any dc on the output + of that channel ahead of the relay of course.
do you have a dim bulb tester?
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Hi Turk, apologies for the delay in replying to you message. I gave up checking after a few days but have now returned to this amp for attention.
I checked for DC on channel A (left chnl) before it enters the relay and I am getting 0V. The is the same for channel B (right chnl). I am getting 17.45V DC on the supply rail to the relays on both sides. By the way, the relay on the faulty channel seldomly clicks in now and when it does it's for less than a second.
I've carried out simple in-circuit diode tests on all of the power transistors but cannot find any with obvious shorts, which I hope is actually the case. I have a sense that this may turn out obe be something requiring less work in terms of replacing an affected component but of course that doesn't count for much at this stage. 😉
I don't have a dim bulb tester unfortunately.
Could you give me some more pointers for things to check if at all possible?
Sorry, I forgot I also checked if sound was also cutting in when the relay kicks in and it is. Sounds clear and clean for that split second, so component testing in the relay area of the circuit. Checked the 1N4148 out of circuit and that's okay. Tested the 3V3 Zener in circuit and that's showing the same as the other channel, so looking at the transistors now...
Yep, but not constantly. If I play music through the channel the channel's LEDs do nothing but, say, once every couple of minutes the music will cut in through the speaker but this isn't necessarily in sync with the prot LED flickering for a second. It will flicker without the music cutting in. Using a process of elimination I have swapped the three transistors over from channel B to channel A along with (what I believe to be) the thermistor nearest this section of the circuit all without any change or improvement. I've also replaced the IN4148 and 3v3 Zener, just in case they were faulty but they don't appear to have been. I am considering swapping out the entire OP transistor block and heatsink, as that'll rule out the OP transistors in one fell swoop but it's a biggish job.
with what your describing sounds like several intermittents are coming out to play.
does it respond to physical shock? does tapping it cause things to be worse or better?
if it responds to physical stimulus look for connection problems with maybe cables or ribbon cables and carefully look for bad/cracked solder joints.
if the metering and indicators aren't functioning i'd look at the op amps on that board as they appear to be comparators that are handling triggering for the output relay.
does it respond to physical shock? does tapping it cause things to be worse or better?
if it responds to physical stimulus look for connection problems with maybe cables or ribbon cables and carefully look for bad/cracked solder joints.
if the metering and indicators aren't functioning i'd look at the op amps on that board as they appear to be comparators that are handling triggering for the output relay.
after re-reading your post you swapped the semi's in the protect section that leaves pretty much the caps those 220 uf 10v ones.
does Q37 have a heatsink?
and while your looking at that what does the voltage rail on that board look like?
and while your looking at that what does the voltage rail on that board look like?
No physical movement, tapping, banging etc, affect the problem. The meter for the right channel (Chnl B) shows the green LED flickering to music following the yellow LED (PROT) illuminating then extinguishing following switch on. However, the left channel (Chnl B) illuminates the yellow LED but then extinguishes followed by the occasional flicker. Since the sound comes through when the relay trips it seems to me to be the protection circuit being triggered by something closer like in the power amp section. I've been working my way back from the output rather than forwards in hope that I am correct.
Yes, correct, I will check those. Q37 does not have a heatsink. It appears to lie flat against the PCB and is screwed through the PCB possibly to the front facia I think, but it's difficult to see fully. It's too hot to touch but I imagine it's possibly within the heat range of the device since the right channel is working through the board.
just so i know, what sort of test did you use to come to that conclusion?
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Really just because the sound cuts in as if it's merely the protection circuit malfunctioning and triggering when there isn't actually a problem. I've just pulled out the relay as I think I accidentally broke it trying to trigger it, but it may have been faulty anyway. Blew the 1N4148 just by it as well. Just ordered a new relay. Fortunately, they're quite cheap. Hopefully arriving tomorrow.
ok so no real test just a conclusion.
i can only go by what your telling me. the amp seems to function no DC on the output and when it's operating things seem normal as in no distortion, sounds clear. that leaves the components that make up the protection circuit and those caps are part of that.
swapping the caps from the other channels protect circuit would have been the quick way but with failing caps even a resistance reading across them can sniff out the bad ones. low voltage caps are always suspect in my books.
i can only go by what your telling me. the amp seems to function no DC on the output and when it's operating things seem normal as in no distortion, sounds clear. that leaves the components that make up the protection circuit and those caps are part of that.
swapping the caps from the other channels protect circuit would have been the quick way but with failing caps even a resistance reading across them can sniff out the bad ones. low voltage caps are always suspect in my books.
Not a conclusion really more an educated guess. 😉 I checked the caps with a component tester and they're okay. That's everything in the protection circuit swapped out now except the relay, which I should get tomorrow. Hopefully that fixes it but I'm surprised a relay could go faulty like that. The amp isn't more than a few years old and never overdriven.
have you gone further with the " led/meter" board problem?
it may still have bearing on the problem. the op-amps there are linked to the relay function, might be worth further scrutiny.
it may still have bearing on the problem. the op-amps there are linked to the relay function, might be worth further scrutiny.
If there is no dc on output and good sound comes through then I too would suspect protection circuit.
If amp is of any age change electrolytics.
I cant add much more without a circuit.
If amp is of any age change electrolytics.
I cant add much more without a circuit.
Thanks - the service manual is available here: GEMINI XPB 750 1600 Service Manual free download, schematics, eeprom, repair info for electronics
You have to wait about a minute for the "Processing..." message under the document preview to disappear, then it changes to a "Get manual" link.
You have to wait about a minute for the "Processing..." message under the document preview to disappear, then it changes to a "Get manual" link.
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