Marshall Stanmore Repair

[Arno2]

Re: Marshall Stanmore Repair

Hi there,

I am willing to not scrap my marshall stanmore as well and reuse the existing enclosure as well as the drivers.
I understood ToxicGumbo and others (https://techfindings.one/archives/3375) have explored this option .

My questions to the group:
1) Has anyone tried to reuse the original crossover ? If yes can you share your experience ?
2) Could anyone identify the crossover itself ? The goop does not help and in case (1) is doable, I may not want to remove the goop to avoid damaging the crossover.
3) @ToxicGumbo: Can you share your experience when you say "the 50watt amp was a bad choice" ? I would have thought a 50w amp was a reasonable option. I was actually thinking of using this one.

Thanks !!

Arno

[ToxicGumbo]

Re: Marshall Stanmore Repair

3) @ToxicGumbo: Can you share your experience when you say "the 50watt amp was a bad choice" ? I would have thought a 50w amp was a reasonable option. I was actually thinking of using this one.

Hey, Arno2. It's a daunting journey, but an enjoyable one and I learned a lot in the process. There are certainly several ways to go about it, too, and you've taken it a step further by trying to isolate the core parts of the existing hardware. I'd actually like to see that work out, but you're correct to point out the challenge of obfuscated design through all that anti-vibration/snooping goop they slopped on the PCB.

In my case, the 50W amp I picked turned out to take a stereo input and split it into two outputs for left and right speakers. Since the Stanmore has one speaker, the objective would be to have left and right combined into a single 50W mono output. One no-no of audio is never to splice stereo input signals together to force "mono" as it can potentially wreak internal havoc due to sound wave conflicts, so I was essentially forced to live with one channel output (left speaker?) for the woofer and rely on the tweeters for more noticeable stereo. No big deal, but it was a bit of a gut punch. I never could find a 50W amp that was guaranteed to output 50W of a combined stereo signal into mono for one speaker. There are hacks to sort of make this happen, but the safest approaches are a bit of a hassle.

I saw and liked the unit you spotted, particularly for the built-in Bluetooth, though I opted to add Bluetooth separately as an independent input choice for the pushbutton selection. Since that's all I use at this point, built-in bluetooth would have been less of a hassle. The one thing that worries me about that unit is the TPA3116 chip. That's the same one on the board I bought and if you read the spec sheet, you're likely stuck with the same situation I had:

https://cdn.badcaps-static.com/pdfs/...d5f959dd7b.pdf

From page 24:

"The TPA31xxD2 family can be connected in MONO mode enabling up to 100W output power."

In other words, the only way to get both Left and Right in a single mono output means you're forced with 100W, which will overpower that driver. You can see in the block diagram on page 13 how the chip takes L & R inputs (LIN*, RIN*) at the very start and produces L & R outputs (OUT*L, OUT*R) under normal 2x 50W mode.

Maybe there's an easy solution to this, but just combining signals before or, especially, after, can possibly turn out nasty. For me, I just gave up looking for an alternative and went with one channel. Would love to hear your thoughts.

[sunnysocket]

Re: Marshall Stanmore Repair

Hi All , Have someone get success to fix stanmore ? I found mine met the same issue with R23 & still try to trace other problems
Thanks

[hann]

Re: Marshall Stanmore Repair

hi im hann, my problem with stanmore is no power. On supply section. Already replaced pwm chip ob2269. Still to success.

[hann]

Re: Marshall Stanmore Repair

here is my board and i drawn a schem to find the culprit

[hann]

Re: Marshall Stanmore Repair

tested some voltage mark with arrows, but still no output

[R_J]

Re: Marshall Stanmore Repair

You should have about 30 volts on the 100/63 cap connected to the diode and 5.1 resistor, The zener diode you have 5 volts on is too low.
Do you have full B+ on the fet drain pin? are the two 0.1Ω resistors on the source good?
When first connected to a/c, the ic should output pulses to drive the fet, that will induce a voltage in the secondaries of the transformer, The run winding should supply the run voltage (20~30v) to keep the ic operating. Check that the winding is not open, the diode is ok, the 5.1Ω is good and the 100/63 is good. Check that zener diode's number to get its value.

[R_J]

Re: Marshall Stanmore Repair

I also see ZD1 drawn in series with the optocoupler, are you sure this is correct? Ususlly the zener is across the opto's output, check that it's not shorted

[hann]

Re: Marshall Stanmore Repair

You should have about 30 volts on the 100/63 cap connected to the diode and 5.1 resistor, The zener diode you have 5 volts on is too low.
Do you have full B+ on the fet drain pin? are the two 0.1Ω resistors on the source good?
When first connected to a/c, the ic should output pulses to drive the fet, that will induce a voltage in the secondaries of the transformer, The run winding should supply the run voltage (20~30v) to keep the ic operating. Check that the winding is not open, the diode is ok, the 5.1Ω is good and the 100/63 is good. Check that zener diode's number to get its value.

thank for the comment, i try measure it again.there is no markings on zener.

[hann]

Re: Marshall Stanmore Repair

I also see ZD1 drawn in series with the optocoupler, are you sure this is correct? Ususlly the zener is across the opto's output, check that it's not shorted

sorry for the drawing, its parallel on the opto. thanks for the correction. great help here.

[hann]

Re: Marshall Stanmore Repair

thank for the comment, i try measure it again.there is no markings on zener.

there is full B+ on fet drain pin, both .1 ohms good, both windings were ok, diode us1m reads .412 volts and ss14 reads .144 on dmm diode test. 5.1 ohms good, 100/63 good.

[R_J]

Re: Marshall Stanmore Repair

Whats the number on the (unmarked) zener diode? if it is bad it could be killing the feedback/run voltage
That ss14 seems to read low, was that check in circuit or out?
Also, check ZD1 that is cross the opto, it could be shorted

[hann]

Re: Marshall Stanmore Repair

Whats the number on the (unmarked) zener diode? if it is bad it could be killing the feedback/run voltage
That ss14 seems to read low, was that check in circuit or out?
Also, check ZD1 that is cross the opto, it could be shorted

ZD3 on pcb with blue band, ss14 check out in the circuit, zd1 is ok.

[R_J]

Re: Marshall Stanmore Repair

5 volts on the transistors collector is too low, find out why and you will likely fix the problem

[R_J]

Re: Marshall Stanmore Repair

Are you sure about how ZD3 and the transistor are drawn? Or is like this? This way the transistor acts like a regulator and the zener diode sets the regulator voltage.
Any other marks, letters, or bands on the zener? A blue band seems to designate Zener, but there is usually another band that tells the zener voltage

[hann]

Re: Marshall Stanmore Repair

sir R_J thanks for the input sir. i have found the fault. its the 3.3/50 volts e cap, replaced it then voila! power restored. i studied the datasheet on the pwm ic. the e cap doesn't charge that is why the ic wont start. a very big thank to you sir.

[hann]

Re: Marshall Stanmore Repair

thank you sir R_J

[R_J]

Re: Marshall Stanmore Repair

Good to see its fixed, That 3.3/50 is a common failure on smps's. and I would have replaced it right at the start. I guess I should have suggested that right away. That cap. needs to charge to the full vcc supplied by the transformer after a couple cycles, if it does'nt the ic will not start and run.

[hann]

Re: Marshall Stanmore Repair

I only tested that cap with analog multimeter that is i didn't see its bad. Hehehe

[petehall347]

Re: Marshall Stanmore Repair

I only tested that cap with analog multimeter that is i didn't see its bad. Hehehe

did you do as i do and see how long meter beeps for ?