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Author Topic: Broken EP (Read 11586 times)

Offline Saint

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Broken EP
« on: 2014.February.26. 23:50:54 »
Ooops, I seem to have broken my Arabic Enterprise. :oops:

I replaced the caps, powered it up, didn't get a picture. Then I compared against my working EP and found I had managed to install the radial caps backwards with negative at the marked end on the PCB. So I switched them all around so that the positive end is at the mark on the PCB, but still no picture.

Wondering what I can have buggered. :roll:

Offline Zozosoft

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Re: Broken EP
« Reply #1 on: 2014.February.26. 23:56:30 »
I think you least killed the caps... using new ones for the second try?

Offline Saint

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Re: Broken EP
« Reply #2 on: 2014.February.27. 00:02:10 »
Quote from: Zozosoft
I think you least killed the caps... using new ones for the second try?
I used the same caps and flipped them hoping not to have killed them. I have spares, so I'll replace them all again tomorrow with new ones. :oops:

Weirdly I had managed to install C9 backwards when I first fixed this Enterprise (which is why I copied the polarity for the rest of the caps), so I'm surprised it has been running!

Offline Zozosoft

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Re: Broken EP
« Reply #3 on: 2014.February.27. 00:13:39 »
Quote from: Saint
I used the same caps and flipped them hoping not to have killed them.
If you have a capacity meter you can check it.
But as I know the electric capacitor doesn't like the reverse polarity. Can explode...

Quote
Weirdly I had managed to install C9 backwards when I first fixed this Enterprise (which is why I copied the polarity for the rest of the caps), so I'm surprised it has been running!
:shock: :shock: :shock:
Very mystic!
« Last Edit: 2014.February.27. 13:11:30 by szipucsu »

Offline fatbob_gb

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Re: Broken EP
« Reply #4 on: 2014.February.27. 09:52:39 »
Do you have UK part numbers for the caps - I have a couple of Enterprises (a newly acquired 64 and my old 128) that have broken 12v lines and very dodgy looking caps throughout. Also the 64 has a broken coil, any idea where I might get a replacement?.

Offline Saint

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Re: Broken EP
« Reply #5 on: 2014.February.27. 10:31:42 »
Replaced all the caps again with new, still black screen. :evil:

Oh dear, I'm not sure what I've broken or where to even start looking at the moment.


I got my replacement caps from eBay (and TR2 transistor), although not these exact links... 

10uf 35v
100uf 25v
etc..

Easy enough to match up.
« Last Edit: 2014.February.27. 10:36:34 by Saint »

Offline Saint

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Re: Broken EP
« Reply #6 on: 2014.February.27. 10:44:01 »
Is there some kind of test ROM Zozo which beeps with the internal speaker? Wondering if there was an easy way to see if it was actually running to any degree but with dead video...

Offline Zozosoft

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Re: Broken EP
« Reply #7 on: 2014.February.27. 10:55:15 »
Quote from: Saint
Is there some kind of test ROM Zozo which beeps with the internal speaker? Wondering if there was an easy way to see if it was actually running to any degree but with dead video...
It is included in the EXOS 2.4, just press down the B key when power on.
Or put the Test ROM segment to segment 00h: if you use 64K EXOS 2.4 EPROM just remove A15 from pin 1 and put back VCC.
Or program the Test rom to separate 16K EPROM, it is at 8000h-BFFFh in the EXOS 2.4 file.

Or there is the original stand alone versions. The OLD just testing, another try to initialize video: copy LPT table and character set to video memory, set up 40 characters mode, and memory testing run in display memory, you can see the caharcter changes during test. It is also beeping.

Offline Zozosoft

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Re: Broken EP
« Reply #8 on: 2014.February.27. 10:57:00 »
Quote from: Saint
I'm not sure what I've broken or where to even start looking at the moment.
Firstly: now all voltages are ok?
For the next: do you have a oscilloscope or least TTL Logic probe?

Offline Saint

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Re: Broken EP
« Reply #9 on: 2014.February.27. 11:05:34 »
Quote from: Zozosoft
Firstly: now all voltages are ok?
For the next: do you have a oscilloscope or least TTL Logic probe?
Ok, I'll try connecting VCC to A15 on the 2.4 ROM and see what happens. It's difficult to tell with modern TV's what is going on, as you may have some messed up video output, but unless the TV recognises it as a valid format, it just says no signal. Not useful for debugging!!

Yes, I have an oscilloscope and logic sniffer. I was wondering where to start... see if the Z80 bus is active?

Offline Zozosoft

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Re: Broken EP
« Reply #10 on: 2014.February.27. 11:28:10 »
Quote from: Saint
Ok, I'll try connecting VCC to A15 on the 2.4 ROM and see what happens. It's difficult to tell with modern TV's what is going on, as you may have some messed up video output, but unless the TV recognises it as a valid format, it just says no signal. Not useful for debugging!!
Keep a old good CRT monitor for a service work :-) Philips CM8833 or a similar.

Quote
Yes, I have an oscilloscope and logic sniffer. I was wondering where to start... see if the Z80 bus is active?
- check the System Clock at U18 pin 12 (8MHz)
- check Z80 Clock at Z80 pin 6 (4MHz)
- check Video Clock at U37 pin 10 (14.237536 MHz)
- check Reset signal on Z80 pin 26 while pressing reset button. One impulse needed for each pressing.
- check 1MHz Clock at expansion bus pin A21
If no reset and no 1MHz then the Dave not running probably it is dead :-(
For the video part check VCAS and VRAS on video RAM ICs (pin 15 and pin 4) and VMUX on U8,9 pin1. These are cyclic signals because the Nick always reading video memory. If no activity then Nick not running...
If these good then check RD, MREQ and M1 signal at Z80 (pin 21,19,27), if all do activity then CPU looks running. Then check ROM CE signal at EPROM pin 20. (I found few partialy dead Dave chips which are not generate ROM or CART signal, this is can be substitued by adding one address decoder IC)

Offline Zozosoft

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Re: Broken EP
« Reply #11 on: 2014.February.27. 11:33:16 »
One note for BEEP testing: plug a speakers/headphones to Tape Out (Stereo Output) connector for the case if internal speaker circuit dead.

Offline Saint

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Re: Broken EP
« Reply #12 on: 2014.February.27. 11:39:28 »
Quote from: Zozosoft
Keep a old good CRT monitor for a service work :-) Philips CM8833 or a similar.
- check the System Clock at U18 pin 12 (8MHz)
- check Z80 Clock at Z80 pin 6 (4MHz)
- check Video Clock at U37 pin 10 (14.237536 MHz)
- check Reset signal on Z80 pin 26 while pressing reset button. One impulse needed for each pressing.
- check 1MHz Clock at expansion bus pin A21
If no reset and no 1MHz then the Dave not running probably it is dead :-(
For the video part check VCAS and VRAS on video RAM ICs (pin 15 and pin 4) and VMUX on U8,9 pin1. These are cyclic signals because the Nick always reading video memory. If no activity then Nick not running...
If these good then check RD, MREQ and M1 signal at Z80 (pin 21,19,27), if all do activity then CPU looks running. Then check ROM CE signal at EPROM pin 20. (I found few partialy dead Dave chips which are not generate ROM or CART signal, this is can be substitued by adding one address decoder IC)
I have a nice Atari SC1224 which would do the trick, but no cable for the EP. Would be handy to have one right now! :)

I've connect VCC to A15, nothing on the speaker, but I do have beeps on the headphones. I assume this is bad? :cry:

I will get the oscilloscope out and check those signals, thanks for the list. One other thing is I was missing one new cap, so C24 is an old possibly dead one.

Offline Zozosoft

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Re: Broken EP
« Reply #13 on: 2014.February.27. 11:52:04 »
Quote from: Saint
I've connect VCC to A15, nothing on the speaker, but I do have beeps on the headphones. I assume this is bad? :cry:
It is good because least partialy working the machine :-)

Offline Saint

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Re: Broken EP
« Reply #14 on: 2014.February.27. 14:32:16 »
Quote from: Zozosoft
It is good because least partialy working the machine :-)
It's not looking too bad so far...

Video Clock at U37 pin 10 is present
VCAS and VRAS activity
VMUX signals present
csync at 15khz
peritel mode switch 12v (10v with scart connected)
activity on RGB lines


But no signal on digital TV. So it looks like the signal isn't constant enough for the TV to accept.