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Messages - sprocket

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Maintenance / Re: One Dead EP128...
« on: 2010.February.21. 07:17:52 »
.....and one year later he responds! :ds_icon_cheesygrin:

Hi!  Yeah, still have my dead EP128 - I hoped it might 'miraculously' come to life when I took it out yesterday (12 months later), but no such luck...  Interesting that another Enterprise suffered the same fate after just being left unused for an extended period, especially an electrical failure.  Repair is further hampered by the DAVE chip being surface-mounted, so most people that even had a motherboard for spares, would not have the means to remove the SMD components (NICK & DAVE) 'cleanly'.  Sad... :smt089

Maintenance / Re: One Dead EP128...
« on: 2008.November.07. 19:31:37 »
I would have no problem whatever replacing SMD's - my last job had me replacing literally hundreds of much smaller SMD devices, so something as 'big' as DAVE/NICK would be no problem at all!  You need the right equipment though, some of which I decided to, ahem,  'hang-onto'... :D

If you knew someone with one for sale, it would be fantastic!!!

Maintenance / Re: One Dead EP128...
« on: 2008.November.07. 00:30:05 »
The 14mhz is present, but there is no 1Mhz coming from DAVE, another indication that this is the faulty component!  I have also checked the components that you suggested and they seem fine.  Looks like I will just have to wait until someone decides to sell a faulty Enterprise and hope the Dave chip is OK! :)  Thanks for all your help and advice, at least I now know a little more about made the EP tick :razz:

Maintenance / Re: One Dead EP128...
« on: 2008.November.06. 20:14:38 »
Zozosoft, hello again!  There's good news and bad news - as expected, the no address/data bus activity was caused by the Z80 RESET line being held low, so once this pin was disconnected from DAVE and wired directly to the reset button, I then had bus activity restored.  Unfortunately, as you pointed out, DAVE also supplies at least one other crucial signal, the rom's chip-enable (CE), and this is always held high, so the rom is never activated!  As a result, the video side cannot be activated either, so no video as well :(  The U37 inverter associated with DAVE's Reset line is fine, and DAVE does not appear to be dry-jointed.  So it certainly looks like the DAVE i.c. is the culprit.   :cry:

Maintenance / Re: One Dead EP128...
« on: 2008.November.06. 01:44:29 »
Maybe I was wrong about no activity on the video connector - the pic below is the best signal I get 'top-side', while probing the bottom connectors, I get random spikes of about 200-300mV!!!  Also, both RAS/CAS of video ram are active which is nice to see :)  Pressing the reset button results in no activity on the Z80 reset pin, so maybe DAVE is the problem!  C4 is also fine.  At least some activity now, which is nice to see... :D

PS - I just realised that Z80 RESET is always low, and pressing the button doesn't effect this either - which doesn't seem right...

Maintenance / Re: One Dead EP128...
« on: 2008.November.06. 00:18:41 »
Zozosoft, many thanks for your comprehensive reply!

Yes, I have only ever used the 'official' EP PSU with the EP128.  Also, both 5v supplies are present.

I decided to go with the Z80-faulty possibility, so have just removed it, added a socket and a good Z80 but no joy!  I tried the old one in a Spectrum and it works fine :(  I also stuck the EP ROM into the Speccy to check address/data bus activity and this seems 'normal', so I assume this is OK, whereas there is absolutely no bus activity when it is in the EP128 :(  All the interrupt lines (INT, NMI, HALT etc.) are at 5v, so that doesn't seem to be the problem either!  Though I do not have a way of connecting a monitor via the video connector, I did scope them and (again!) absolutely no activity there either.  It's beginning to look like one of those SMD's is at fault, either the NICK or DAVE i.c's...

Please say it isn't so... :D

Maintenance / One Dead EP128...
« on: 2008.November.05. 17:09:12 »
Hi.  It's great to see there is still a thriving EP group!!!

I bought an Enterprise128 almost 15 years ago, to add to my retro-collection, but never really used it except for occasionally switching it on to see that it still worked.  My latest check reveals that all is not well - it will not power-on at all...

Apart from being able to confirm that the little red LED indicates power-up, I have also been able to deduce that all supply voltages are present, (+5v, +12v) as are the 4.433619Mhz, 8Mhz and the derived 4Mhz, which is being supplied to the Z80.  However, there appears to be no address/data bus activity at all, nor is there any RF (PAL) being produced by the modulator (no raster of any kind).

btw, the PCB is undamaged and in perfect condition, despite the computer having been dumped in a shed for many years.  Is there anyone with EP repairs experience, and if so, could you shed any light on exactly what component may have failed???


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