Author Topic: Got amstrad pcw 8256 but the fun don't lasted very long ...... :O  (Read 13616 times)

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Offline Sebastian Blanco

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Hi!, ok after my first pcw 6128 show up to be in bad conditions i was lucky and scored a PCW 8256 upgraded to 512.
Disassembled the guy a hooked a ribbon to a  external 3.5 drive burned cp/m floppy disks games and played for an hour all nice and dandy but .... ! then the unit suddenly turned off and never turned on again .... :'(

The computer don't even power up the power led is off all the time seem to be a power supply related issue.

Then i have an idea  :P get it to your local repair center!  ;D , so i go to a big repair shop i used to take stuff some years ago. But thinks changed a lot, then you have to see the face of front desk employee was like i have taken an alien artifact to the shop, he  called the manager and the manger stared at the PCW like he have seen Jesus Christ in person, then he call the shop owner from the back and when he take a look at the PCW his face was like "what the bloody hell is this thing".
Then i was friendly escorted to the exit door and get my ass kicked from the shop, so seem that I'm alone on getting the thing fixed :D.

Somebody now where i can start, or some common culprit on the analog board ?.

Thanks.

Offline GeoffB17

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Sad news.


When it 'died', was there any noise, or smoke, or smell?   If not, then it might be something minor, but you never know.


I'm sure there's folks here who will suggest what component may have died.


I have to admit, when I attached a 3.5" drive to my PCW, I never tried to use the PCW power supply.   I got an external 5v power adaptor, and I've always used that.   Never had any problem.   I always understood that the PCW power supply was weak, Amstrad used the 3" drives because their power requirements were lower than usual.


Best of luck.


Geoff

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A very stupid suggestion, I know, but have you already checked the fuse?

Offline GeoffB17

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If it's JUST the fuse, then maybe you could cure by using separate power supply for 3.5" drive, once fuse replaced.  I think I've read that 3.5" drive can take out fuse.   There are various models of drive, but maybe some take more power than others.   Maybe the one you have IS drawing too much power, and it managed for a while then went.
If there was no bang, or crack, or smoke, or smell, then the fuse is pretty likely.


Geoff

Offline GeoffB17

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Just checked circuit diagram - there's a 2A fuse in one corner of the main PCB (near where mains comes in, I assume).   Check if that's OK.


Geoff

Offline Munchausen

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Then i have an idea  :P get it to your local repair center!  ;D , so i go to a big repair shop i used to take stuff some years ago. But thinks changed a lot, then you have to see the face of front desk employee was like i have taken an alien artifact to the shop, he  called the manager and the manger stared at the PCW like he have seen Jesus Christ in person, then he call the shop owner from the back and when he take a look at the PCW his face was like "what the bloody hell is this thing".
Then i was friendly escorted to the exit door and get my ass kicked from the shop, so seem that I'm alone on getting the thing fixed :D .

This is such a funny image, it should be in a sketch show (I lolled)  :laugh:

We used to have a TV repair shop near by that probably could have fixed something like this. But they've all closed down. That one was an end of terrace house turned into a shop, now it's just an end of terrace house again, but with oddly large windows  ;D

I hope you get your machines fixed. If all else fails give @Bryce a shout. Just wait for him to soak all the water up in his basement with Plenty kitchen towels ("wettable, wringable, strong as bull") first.
 
« Last Edit: 02:16, 02 July 16 by Munchausen »

Offline CraigsBar

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<snip>

I hope you get your machines fixed. If all else fails give @Bryce a shout. Just wait for him to soak all the water up in his basement with Plenty kitchen towels ("wettable, wringable, strong as bull") first.

I think Bryce has dried out again. The basement I mean. As my megadrive2 came back all crystal clear audio modded, country and 50/60hz switched, and most importantly with a mild CPU overclock (it now runs at 10mhz, not 7.16) and there is not a drip anywhere.

Craig.
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Offline Sebastian Blanco

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Thank you guys for the reply, the funniest thing was that before going to the shop,  called and explained that the computer was very old and the complete unit was in the monitor that if they where sure that they still fix crt monitors, the clerk assured me that they can fix anything and there's no problem just bring it on. The guy when i was there confessed that he think it was a all in one imac or something like that :P.

The unit turned off next to me while i was using it and there's no smoke no sound nothing just the screen turn off.
I have checked the fuse and is ok, i have some electronic experience and studied tv and radio repairer when i was young, but that was like 20 years ago and have forgotten a lot.

The disk drive i connected just use 5v and i have disconnected the internal 3¨ considering the PCW can take 2 3¨ drives the load from a modern 3.5 drive sure could be a lot less than the original ones.

Offline Audronic

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Hi Sebastian


Can you remove/Unplug both cables from the 3.5" drive and see if the unit powers up.


Also (Yeh i Know) Please check that the power plug has all the wires connected and that the power point has power going to it .


Good Luck      Ray



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Offline Sebastian Blanco

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Yes i have tested removing all hardware possible, even the digial board but the unit never turn on

Offline Munchausen

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Have you got a multimeter? First thing to check is the power rails

Offline Bryce

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Can you post some pictures of the component side of the PCB. The failure may be visible.

Bryce.

Offline Sebastian Blanco

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Ok get a multimeter to the job, using it i can get voltage even to the secondary on the isolation transformer that go between the high voltage area and the low voltage one but i´m working blind no shematics and no information off the correct voltages i have to find wat i can say for sure is that the rectifier diodes the fuse and resistors in the start of the circuit are ok.

Here go the pics
























Offline Audronic

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There is a service manual in the WIKI




Amstrad PCW 8256-8512 Service Manual


Good luck     Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Offline Bryce

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I'll take a close look at the pictures later when I have time, however, the dust alone is enough to stop it from working. Give it a decent brushing with an unused paintbrush first.

Bryce.

Offline ||C|-|E||

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It is certainly a bit on the dusty side, to put it lightly  :-\ If I were you I would try to wear a mask (or a wet cloth over the mouth and nose) to prevent allergies and complications.

Offline SRS

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Second picture looks "toasted". Whats on the other side ?

Offline Executioner

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My 8512 has the same problem, but I bought it knowing it had the problem. No power indication at all. I need to extract the PSU soon and have a look, but I need to know how to avoid getting a shock from the monitor high voltage.

Offline Bryce

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Second picture looks "toasted". Whats on the other side ?

That's the bottom side of the STK7308. That's a switching regulator and runs hot in normal use. It's also the most likely part to have failed (if the fuse is still good).

Bryce.

Offline Sebastian Blanco

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Will try to get some compressed air can to wipe clean the board, but today as almost always is rainy like hell here.
 Also there a way to check if the stk7308 is bad i get the schematic from the part but is in Chinese you know a way to check for some expected voltages on the output or something.

Offline GeoffB17

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According to my service manual, voltages on the pins should be:


1: 0.2
2: -20.0
3: -27.5
4: 0
5: -9.0
6: 0
7: 0
8: -2.0
9: -3.0
10: 0
11: 0.24


14: 7.9
15: 7.9


Pin 1 is furthest from the edge of the pcb, pin 15 is nearest the edge.  Pins 1 - 11 are in a block, 14 and 15 are separate.


Geoff

Offline Bryce

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Check the voltage across C5005, but be careful poking around that part of the circuit, it can kill you. You should get about 220 to 240VDC. Then I'd check the voltages (Meter set to AC) across the inputs of T5001 (the transformer). If the STK is broken you are probably getting nothing or a DC voltage on the inputs.

If you're not sure about what you're doing, don't do it.

Bryce.

Offline Sebastian Blanco

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Thank you very much from your help, ok i checked the voltages across:
IC5001
pins from 1 to 13 i got 0v.
pin 15 is 304v DC.
pin 14 is 1000v DC and my multimeter get out of scale.
using the ground from the heat sink screws.

T5001
transformer input pins 1, 2, 3 got 313v DC using pin 4 as ground.

C5005
300v DC between pins

Seem the stk is death ass you say sir, but the high voltages on pins 14 and 15 are normal ?.

Offline Audronic

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@Executioner


If you want an STK7308 I have one here (Victoria) In a WORKING colour monitor board.
Cost " a Smile " .




Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
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Offline Bryce

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Thank you very much from your help, ok i checked the voltages across:
IC5001
pins from 1 to 13 i got 0v.
pin 15 is 304v DC.
pin 14 is 1000v DC and my multimeter get out of scale.
using the ground from the heat sink screws.

T5001
transformer input pins 1, 2, 3 got 313v DC using pin 4 as ground.

C5005
300v DC between pins

Seem the stk is death ass you say sir, but the high voltages on pins 14 and 15 are normal ?.

Hmmm, the STK is most likely broken, but I'd also question your multimeters functionality. What model is it? Pins 14 and 15 are connected together both inside and outside the STK, so they can't possibly have different voltages.

My suggestion would be to swap the STK and all electrolytic capacitors around it. When you have the STK and caps off the board, check that the diodes are stilll doing their job.

Bryce.