Marshall Stanmore Repair

[VanDivX]

Re: Marshall Stanmore Repair

Can one edit one's posts here? Like at least to correct some spelling? I don't see how to do that.

Anyway, I measured across the two yellow blocks either side of the smaller transformer and they measure 0.8uF, I suppose then they are capacitors then and are OK. One of them is marked as CX1 on pcb.

I tried to take picture of the markings on the 'transistor' mounted on the black heatsing right behind that big capacitor I removed for measuring and it says 'F' 1FO5BR FDPF 10N60NZ

Googling around, I found it is FDPF10N60NZ ECAD Model
Fairchild Semiconductor MOSFET N-CH 600V 10A TO-220F

MOSFET is another possible culprit - all I know is it sensitive to electrostatic discharge and it passes current depending on input... that might be why I don't measure short on AC input, it needs powered up to short it (if it is faulty). I just don't know how to check it, if someone has an advice how to measure on it, I'd be grateful. Keep in mind I can't power the pcb up to measure voltages on it.

[VanDivX]

Re: Marshall Stanmore Repair

Hi there, new member... I have this expensive piece of hardware and when I opened it, I found the fuse blown but replacement blows again. Clearly I am the 'Case 3' in the original post - "no led, fuse blown".

My skills in this regard are very mixed, I know how basic electronic parts work but my radioamateur days ended when IC circuits came on scene. I did careful visual inspection but nothing looks bad. I was hoping for bulging capacitor top or something of the kind but it all looks OK.

I suspect some short in the area of power supply, in particular I suspect the big capcitor 150uF/400V. Also perhaps the rectifying bridge KBL406 perhaps?

The nature of this fault limits me to measuring only on un-powered PCB and I am aware that measuring resistance or continuity can be misleading...

I started by removing the above mentioned capacitor and when I got it out, it measures ~145 uF, which means it is OK.

Then I tried measuring on the rectifying bridge and I get continuity or about 1ohm across the +/- and (dc output) legs, the two inner legs to which AC is connected show now short, resistance is 'infinite', it is like the multimeter leads are not touching anything (0L).
Also no short to the two outside legs of the bridge from these two inner ones (I swapped multimeter leads polarity in case it matters - since diodes pass current only one way I presume.

The first transformer coils have continuity, the two yellow blocks on either side of it do not show short or any resistance (0L), so I am at the ends of what could be shorting the A/C input. I even tried 2A/250V fuse but it blows instantly as well.

Funny thing is, if I measure continuity or resistance across the AC input (the two prong socket where 120V comes in, with good fuse inserted, it shows no short, or resistance (infinite, or 0L). Maybe some semiconductor device mounted on heatsink when powered, it shorts instead of doing whatever it should be doing? So I don't measure the short circuit?

I took many photos of both sides of PCB, in Large format with my compact camera, in case it might helps somebody with their troubleshooting, like values of parts some people asked for. My PCB is luckily not that much plastered with the goop like what other peoples' pictures show. I uploaded the whole series of them to Mediafire here - I suppose the forum has upload but since these pics are large and many, I thought to upload them externally.

http://www.mediafire.com/file/8txzsi..._2019.rar/file

[dysk1]

Re: Marshall Stanmore Repair

LM317 had the same protector signal as the inverter. After desoldering another resistor all voltages have already appeared correct.
Unfortunately, no functions are still working.

[R_J]

Re: Marshall Stanmore Repair

Type this into GOOGLE: LM317 DATASHEET

[dysk1]

Re: Marshall Stanmore Repair

Update:

What voltage should come out of LM317??

[dysk1]

Re: Marshall Stanmore Repair

A larger picture is attached.

Edit:

I measured that instead of 3V on TAS5508C power supply I have 0.6V

[R_J]

Re: Marshall Stanmore Repair

Image is too small

[dysk1]

Re: Marshall Stanmore Repair

Hello,

I also have a device that doesn't work. After switching on the power supply instead of 30V I have 8.3V.
I drew a converter feedback diagram. I came to the fact that it blocks the signal fed from the 12LE5A16S2 processor to the R147 resistor. After desoldering the R147 resistor, the inverter works correctly and has 30V, but this is not the solution to the problem.
I am asking for any suggestions.

[hann]

Re: Marshall Stanmore Repair

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

the pointer of my multimeter go straight to zero ohm and slowly going back. i thought its ok. but i already suspected the ecap as i have read on the datasheet. that it should charge to make the ic run.

[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 ?

[hann]

Re: Marshall Stanmore Repair

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

[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

thank you sir R_J

[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.

[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

[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

[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

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

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.

[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.