Hey folks.
I've only seen comments on Marshall Stanmore speaker repair through YouTube videos. Perhaps the lack of internet chatter is related to the dual forms of goop Marshal splatters the PCB with to discourage repair attempts. Nevertheless, I'm attempting to repair one.
Some of the problems I've seen with these devices:
1. Seems to most commonly be fixed by nuking all Bluetooth devices that have been assigned to the device and then re-pairing a specific device. Less frequently, it could mean the Bluetooth card (soldered to the PCB) has become damaged in some manner. There's a 4 port header on the PCB in the middle of the raised panel labeled "shield" that can be measured for proper voltage: The one closest the Bluetooth module (and right next to a capacitor also poking through the shield) should measure around 5VDC, the next pin being ground. If this voltage is much lower, one person discovered that the voltage to the MCU is too low and traced it back to the 8-pin surface mount DIP MC34063A in the middle of the board. These are cheap to replace.
2. See above about the MC34063A chip. It's also possible that the amp went out in a non-catostrophic manner: Check voltage at the LM317T voltage regulator and FMG23S rectifier (U5 & D8) that drop from the PCB and are bolted to the backplate. The MCU itself might also be damaged.
3. If a surge occurred and replacing the fuse doesn't solve the problem, this could be a fault of the primary (power supply) or secondary (cold) side of the PCB. Given all the goop spread around the PCB, you'll have a very complicated time diagnosing this problem. The power supply is a 100-240V SMPS with some "standby mode" circuitry thrown in for European compliance. A large DC/DC transformer sits between the hot and cold sides and--on my model--is labeled (with a generic sticker) "TRISTAR 13030122". I can't find any additional markings and TriStar appears to have been a redistributor of electronics parts before they were bought and absorbed by another company.
4. This frequent and faint clicking is the SMPS finding a fault and attempting to see if its cleared before enabling full power. Check the bridge rectifier, voltage at the transformer, etc., but be aware this is the hot side and that you have AC and coarse DC.
My Stanmore's problem is #4. After checking what I could, I removed as much goop as possible and disconnected the transformer on the cold side and still had SMPS clicking. Removing the transformer outright stopped the clicking. Given the fairly inaccessible components, my hope is to ignore or chop the hot side and use an independent SMPS. Of the 5 pins on the cold side of the transformer, two are ground, one leads to the amp components (possibly 18-24VDC based on component max ratings and wattage demands), one is inverted, and I haven't completed tracing the other (perhaps those two are -/+ polar opposites...-12/12VDC?).
I'll spend some time re-evaluating this, but the two exacts that I'm looking for:
Sadly, I knocked R23 off with removal of the transformer.
It's entirely possible, in any case, that problems with a power supply are a result of secondary issues (or vice-versa), but at least knowing the above information gives me a fighting chance. I haven't seen any parted out Stanmores, so it's a costly gamble to buy another broken one.
-Jeff
I've only seen comments on Marshall Stanmore speaker repair through YouTube videos. Perhaps the lack of internet chatter is related to the dual forms of goop Marshal splatters the PCB with to discourage repair attempts. Nevertheless, I'm attempting to repair one.
Some of the problems I've seen with these devices:
- Power LED, no audio through Bluetooth
- Power LED, no audio through any source or faint clicking in speakers
- No power LED, blown fuse
- No power LED, faint clicking in power supply
1. Seems to most commonly be fixed by nuking all Bluetooth devices that have been assigned to the device and then re-pairing a specific device. Less frequently, it could mean the Bluetooth card (soldered to the PCB) has become damaged in some manner. There's a 4 port header on the PCB in the middle of the raised panel labeled "shield" that can be measured for proper voltage: The one closest the Bluetooth module (and right next to a capacitor also poking through the shield) should measure around 5VDC, the next pin being ground. If this voltage is much lower, one person discovered that the voltage to the MCU is too low and traced it back to the 8-pin surface mount DIP MC34063A in the middle of the board. These are cheap to replace.
2. See above about the MC34063A chip. It's also possible that the amp went out in a non-catostrophic manner: Check voltage at the LM317T voltage regulator and FMG23S rectifier (U5 & D8) that drop from the PCB and are bolted to the backplate. The MCU itself might also be damaged.
3. If a surge occurred and replacing the fuse doesn't solve the problem, this could be a fault of the primary (power supply) or secondary (cold) side of the PCB. Given all the goop spread around the PCB, you'll have a very complicated time diagnosing this problem. The power supply is a 100-240V SMPS with some "standby mode" circuitry thrown in for European compliance. A large DC/DC transformer sits between the hot and cold sides and--on my model--is labeled (with a generic sticker) "TRISTAR 13030122". I can't find any additional markings and TriStar appears to have been a redistributor of electronics parts before they were bought and absorbed by another company.
4. This frequent and faint clicking is the SMPS finding a fault and attempting to see if its cleared before enabling full power. Check the bridge rectifier, voltage at the transformer, etc., but be aware this is the hot side and that you have AC and coarse DC.
My Stanmore's problem is #4. After checking what I could, I removed as much goop as possible and disconnected the transformer on the cold side and still had SMPS clicking. Removing the transformer outright stopped the clicking. Given the fairly inaccessible components, my hope is to ignore or chop the hot side and use an independent SMPS. Of the 5 pins on the cold side of the transformer, two are ground, one leads to the amp components (possibly 18-24VDC based on component max ratings and wattage demands), one is inverted, and I haven't completed tracing the other (perhaps those two are -/+ polar opposites...-12/12VDC?).
I'll spend some time re-evaluating this, but the two exacts that I'm looking for:
- The DC values on the three cold-side transformer pins closest to the center of the PCB
- The label/value of resistor R23, between the transformer and outer PCB edge
Sadly, I knocked R23 off with removal of the transformer.
It's entirely possible, in any case, that problems with a power supply are a result of secondary issues (or vice-versa), but at least knowing the above information gives me a fighting chance. I haven't seen any parted out Stanmores, so it's a costly gamble to buy another broken one.-Jeff
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