Marshall Stanmore Repair

[petehall347]

Re: Marshall Stanmore Repair

cant enlarge your pic .. from what i see you may be correct ..looks like it could be 821
82 then 1 for one zero . 820

[hedefalk]

Re: Marshall Stanmore Repair

Update: it was sooty and super hard to read, but I think it's in the low range, hundreds of ohms. It was a lot of work to get these pictures, but I'm pretty sure it ends in X21, so I'm guessing 821 - 820R? However, I measured it now to 1.14K with a DVM. It could be all the soot?

https://drive.google.com/open?id=0B0...Y0MGdObzVZNVZz


Update2: Yeah, scraping a bit of soot off I got down to 1K.


I'm going to try to clean up those pads and solder on a 1/4 W 820R and see where that gets me… Original error could of course be something else, but maybe that resistor was under dimensioned in effect? Maybe this will just make something else fail instead but yeah, worth a shot.

[hedefalk]

Re: Marshall Stanmore Repair

Can anyone tell the values of R23 (a small smd resistor near the big transformer, next to the optocoupler) and U15 (the amplifier IC under the heatsink on the backside of the PCB)?

I marked the locations of them in my photos.

+1 on that question. I was just about trying to answer it and was just to measure it in circuit with a multimeter and it came right off. It was all sooty and black. I guess it has burnt and that this is a common issue?

https://photos.app.goo.gl/gaj3qpH5SIYIXwMP2


My symptom was however a low hizzing/buzzing sound, not clicking.

[wiru]

Re: Marshall Stanmore Repair

Can anyone tell the values of R23 (a small smd resistor near the big transformer, next to the optocoupler) and U15 (the amplifier IC under the heatsink on the backside of the PCB)?

I marked the locations of them in my photos.

[GilbertoS]

Re: Marshall Stanmore Repair

Hi I'm from Mexico I have the same Isue did you have more info ?

[Zygoat]

Re: Marshall Stanmore Repair

Bonjour
sur ma carte, c'est un OB2269CP.

Bon courage

Zygoat

[silver035]

Re: Marshall Stanmore Repair

my u1 ic chip melt down I can't read mark.can you tell me mark from the ic please?

[ToxicGumbo]

Re: Marshall Stanmore Repair

For reference, here are a couple images of my PCB, top & bottom, as I'm viewing and directionally referring to them.

[ToxicGumbo]

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. Power LED, no audio through Bluetooth
2. Power LED, no audio through any source or faint clicking in speakers
3. No power LED, blown fuse
4. 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