Hi guys. I have a problem with XM-3040 (not F) power amplifier. I can't find exact schematic for this device, so all my measurements and inspections are based on XM-3040F schematic. I have found a few inconsistence between them and they look as if the have great meaning for my case.
On schematic for XM-3040F there is R577 and C569 connecting primary and secondary grounds on both sides of transformer. In my device tose grounds are completely separated. And this would be OK, but protection circuit (UPC1237HA) is power supplied from secondary side and drives transistors connected to primary side. I wonder how it worked in original state. I have checked voltages on its pins and they look OK, as if there is no demages in circuit that should trigger protection.
Pin | Voltage
1. | 0V
2. | 0V
3. | 0V
4. | 0.74V
5. | 0V
6. | 10.5V
7. | 1.8V
8. | 3.5V
of course those are voltages measured in reference to ground on secondary side. When I change reference point to primary side, than all voltages will increase +3V. One more thing. When I soldered out UPC1237 and shortcircuited pin 6 to pin 5 (secondary ground) relays and LED only turned off for a very short time (less 100ms) and returned to original state (turn on). When I shortcircuited pin 6 to primary ground, relays are turne off as long as keep this connection.
So my questions are:
- does anyone have schematic for this model without 'F' on the end?
- can anyone explain me how this should work when circuit from secondary side drives circuit from primary side with complete galvanic isolation?
- does anyone have any idea what can be wrong?
On schematic for XM-3040F there is R577 and C569 connecting primary and secondary grounds on both sides of transformer. In my device tose grounds are completely separated. And this would be OK, but protection circuit (UPC1237HA) is power supplied from secondary side and drives transistors connected to primary side. I wonder how it worked in original state. I have checked voltages on its pins and they look OK, as if there is no demages in circuit that should trigger protection.
Pin | Voltage
1. | 0V
2. | 0V
3. | 0V
4. | 0.74V
5. | 0V
6. | 10.5V
7. | 1.8V
8. | 3.5V
of course those are voltages measured in reference to ground on secondary side. When I change reference point to primary side, than all voltages will increase +3V. One more thing. When I soldered out UPC1237 and shortcircuited pin 6 to pin 5 (secondary ground) relays and LED only turned off for a very short time (less 100ms) and returned to original state (turn on). When I shortcircuited pin 6 to primary ground, relays are turne off as long as keep this connection.
So my questions are:
- does anyone have schematic for this model without 'F' on the end?
- can anyone explain me how this should work when circuit from secondary side drives circuit from primary side with complete galvanic isolation?
- does anyone have any idea what can be wrong?
Now it is even more weird. Having only resistors between pin 8 <-> 7 and between pin 7 and ground, voltage on pin 7 after power on is 0V after about 1 second jumps to 1.6V and falls again to 0V, while on pin 8 it is stable 3.5V. I'm going to check this resistor 33k between pins (8,7) but it looks like this input drives this voltage.
Ok, maybe this IC needs to be replaced, but how to drive transistor for relays to turn on them? Let's assume that this IC works. When there is no demage pin 6 (out) whould be low, if any protections will trigger, then output should goes high and relays should be turned off. When I take out this IC and shortcircuit pin 6 to pin 5 (gnd) relays don't remind in off state. they only 'click'. So how to drive base of this transistor?
Sounds like you have a path forward, but perhaps the xm-4040 manual would have some useful info, or more clarity anyways.
SONY XM-4040 SM Service Manual download, schematics, eeprom, repair info for electronics experts
SONY XM-4040 SM Service Manual download, schematics, eeprom, repair info for electronics experts
phase - thank you for this schematic. I can see, that there exactly the same solution like in 3040F. There is C909 and R812 connecting grounds on both sides. Without this, currents in circuits on both sides of transformer are independent and can't flow through one line (Kirchoff's law). In my device I can't find such elements that is why I am asking about schematic to this device (without 'F')
I decided to check if shortcircuiting pin 8 and 7 will help but it didn't. On Pin 4 there is now 0.3V so it looks that this IC is dead. I removed this part and placed npn transistor (E - to GND, C - to resistors from relay driver transistor, B - vie resistor, to delay circuit from pin 7). As I expect, relays still 'clicks'. So I assume, that without approprite schematic I will not find right place to fix. There are two solutions: build this delay circuit on primary side and drive relays directly OR use optocoupler and keep isolation between primery and secondary side.
The primary and secondary grounds are connected together when a signal source with a grounded shield is connected to the RCAs.
Why not replace the IC?
There are protections circuits that feed that IC to protect from over-current, thermal, DC offset... A simple switching circuit won't offer the same protection.
Why not replace the IC?
There are protections circuits that feed that IC to protect from over-current, thermal, DC offset... A simple switching circuit won't offer the same protection.
That one IC I have had just burnt was already a replacement for original. Original was completely broken. Last experiment showed, that new IC does not fix the problem but from what you have written it make sense to check with new one again. I agree, that this IC gives more protection then simple transistor, but if nothing works then even minimal protection is always better then broken device.
These are some notes I have for the IC. Along with the datasheet, you should be able to determine if the input to the IC is causing a problem or whether the IC is defective. It's possible that all ICs are either counterfeit of NOS (which may make them 20+ years old).
Pin 1: overload detect (must be below 0.7v -> generally at 0v)
Pin 2: DC offset detect (must be between +0.62 and -0.17 -> generally at 0v)
Pin 3: reset mode (grounded to require that power be cycled to re-engage relay)
Pin 4: AC detect (must be above 0.74v)
Pin 5: ground (measure other voltage with reference to this pin)
Pin 6: ground for relay (near ground to engage relay, near supply voltage for relay during mute/protect)
Pin 7: mute delay (must be above 2.06v)
Pin 8: supply (generally between 3.0 and 3.8v)
Pin 1: overload detect (must be below 0.7v -> generally at 0v)
Pin 2: DC offset detect (must be between +0.62 and -0.17 -> generally at 0v)
Pin 3: reset mode (grounded to require that power be cycled to re-engage relay)
Pin 4: AC detect (must be above 0.74v)
Pin 5: ground (measure other voltage with reference to this pin)
Pin 6: ground for relay (near ground to engage relay, near supply voltage for relay during mute/protect)
Pin 7: mute delay (must be above 2.06v)
Pin 8: supply (generally between 3.0 and 3.8v)
Perry, thank you for that. Fortunately I was able to discover purposes of each pin before I started writing on this forum 
. For me the best hint is that those ground will be connected through source ground. I always treat such device as stand alone organism and I would expect, that it will work no matter there is signal or not. I will connect grounds and I'm pretty sure, that it will work with new IC.
. For me the best hint is that those ground will be connected through source ground. I always treat such device as stand alone organism and I would expect, that it will work no matter there is signal or not. I will connect grounds and I'm pretty sure, that it will work with new IC.- Status
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