Amstrad GT-65 Green Screen Monitor not working

[Zyphon]

Hello to all Amstrad CPC enthusiasts,

My name is Michael and I am new to this forum, I just thought I was say hi to the community and I look forward to joining this CPC community.

I recently became the proud owner of an Amstrad CPC 464 computer with the GT 65 Green Screen Monitor plus the MP-1 modulator.

The 464 and the MP-1 work fine (although the MP-1 transformer does make a humming sound) and I am able to use the 464 through my TV via the RF output of the MP-1.

However, my GT 65 appears to be dead. I have done the obvious like check the 13amp fuse and that is fine and when I switch on the monitor, if I place my ear to the back of the monitor I can hear the transformer hum. However there is no picture and looking through the grill the tube isn't lit and it doesn't send any power to the 464 itself.

I was wondering if there any common known problems with these monitors that might help me diagnose the problem?

My next port of call will be to leave the monitor off overnight in case the tube holds any dangerous voltage and then remove the back and check for bad or blown caps other than that I am at a loss as to what to do. I downloaded the GT 65 schematics from this site and hope that might shed some light on the problem.

If anyone has any other suggestions then I would be most grateful. 

Thanks in advance.

Kind regards,
Michael

[Bryce]

Leaving the Monitor over night won't discharge the circuit enough. It will still have enough charge to seriously hurt you in the morning, and possibly for a few weeks depending on what's broken.

By the sounds of it, it's not fixable anyway (and I'm normally the last person to accept this fact). It sounds like the HT transformer is probably dead and that's not something you can swap easily. Do you know where it was stored over the years? This is most likely what killed it.

Bryce.

[Zyphon]

Hi Bryce,

Thanks for your response. To be honest I don't know where it was stored. A friend of mine rescued the CPC 464. He was out walking one day and some guy was about to throw the whole lot in a skip. My friend knows I collect retro computers and asked the guy if he could have it. So luckily for me I got this wonderful piece of kit for free!

I can only assume that it was either stored in a loft or in a garden shed judging by the look of the exterior. I guess I could take a couple of photos of the inside, maybe this may give some clue as the condition of the components.

Alas, I fear you are right and to be honest throwing the monitor away (as much as it pains me) looks like the only viable option as to fix it might not be possible.

Even if I could send it to a computer repair shop it is doubtful that they would have the replacement parts.
I might just go for modding the CPC 464 with a scart lead or the modern day monitor mod.
Thanks again for the advice, I really appreciate your help. 


Kind regards,
Michael

[CanonMan]

I guess I could take a couple of photos of the inside, maybe this may give some clue as the condition of the components.

Yes please! There might not be much wrong with it 

[Bryce]

If it was a colour monitor I would be more likely to investigate further, but a GT65? I don't know. You already have an alternative power supply sorted, so all that's missing is a SCART cable, which is easy to make and you'll have a CPC with decent colour.

Post a few pictures of it anyway, just out of interest.

Bryce.

[beaker]

Can I recommend the scarts from retro computer shack? A little pricey but very good quality and fast delivery. I am using them on my 6128 and Megadrive on my large plasma and the image is sharp and the colours are rich.

Amstrad CPC 464 & 6128 Gold Plated RGB Scart Lead / TV Cable | eBay

[Zyphon]

Can I recommend the scarts from retro computer shack? A little pricey but very good quality and fast delivery. I am using them on my 6128 and Megadrive on my large plasma and the image is sharp and the colours are rich.

Amstrad CPC 464 & 6128 Gold Plated RGB Scart Lead / TV Cable | eBay

Hi Beaker,

Thanks for the your suggestion. I already use Retro Computer Shack, they are fantastic and I bought some disk drive belts from them for my Sinclair ZX Spectrum +3. I go there for all of my retro computer/console scarts. Great quality too. 

@Bryce & CanonMan

I will hopefully have some time to take some photos of the monitor tomorrow and i will attach them once I do, thanks for the help once again.

[Zyphon]

Hi guys,

Sorry for the late response I had internet trouble yesterday and I had family up so this delayed me posting.

An update.

Great News! Success the monitor is now working! 

I am so over the moon I can't contain myself. I took the back off the monitor and then removed the screws that hold the main motherboard chassis. In doing so I could see there were 2 glass fuses that were obstructed from view when I originally looked at the board.

I replaced the 2amp glass fuse with a 1.5amp glass fuse (the only value fuse I had to hand at the time). I re-connected everything screwed the back of the monitor back and hoped for a bit of good fortune that this was the issue and there wasn't anything else going on untoward blowing the fuses, and voilà! 

I plugged the 5V output and Monitor cables to my CPC 464, switch on the monitor saw a flick on the screen, powered on the 464 and she breathed into life! 

I have been so lucky throughout the whole process getting the 464 with monitor and MP-1 for nothing, it came with Chuckie Egg (one of my all-time favourite games) and now works great.

All I need to do now is clean it up and vacuum the dust on the inside of the Monitor and CPC 464 and try to restore them to their former glory best I can.

Am I o.k. using Isopropyl alcohol to clean the residue from the motherboards? I have used this in the past on my other retro computers and it cleans them up well.

Once again, thank you all so much for your suggestions. I am glad that this was an easy fix and didn't end up being a drawn out one.

Once I get the machine cleaned up, I might post a vid on YouTube of it working. Pictures below:

 

PS: I Have circled the culprit in red and indicated the problem fuse with the red arrow.

Thanks again. 

[CanonMan]

Great news

See, I told you there wouldn't be much wrong with it!

It's not in my nature to bin stuff that could well be repairable, so I always open things up and have a look before I decide...

[Bryce]

Good to hear and seriously easy fix. Congrats,

Bryce.

[Zyphon]

Great news

See, I told you there wouldn't be much wrong with it!

It's not in my nature to bin stuff that could well be repairable, so I always open things up and have a look before I decide...

Yes, you were right.  I had my fingers crossed that it might be something simple. I am normally not that lucky, but I am delighted it worked. I agree with you as I don't like to give up and bin stuff, it was just given the age of the monitor ad the condition it was stored in. I thought it have more serious problems.

It's a testament to how well these things were made back then.

Good to hear and seriously easy fix. Congrats,

Bryce.

Thanks. Also thank you for your help and advice from the both of you. I really really appreciate your help in this matter.

Also thanks to Beaker for the link to that scart lead at the Retro Clinic Shop. I will definitely buy one. I am a hobbyist also so I may even make my own just for the fun of it.

Cheers all. 

[Bryce]

Well if you can solder two wires together, then making your own is a lot cheaper. All the instructions are on the Wiki (several versions): TV SCART cable - CPCWiki - The Ultimate Amstrad CPC Community & Encyclopedia!
I would suggest using my "Alternative" version, because it doesn't involve batteries and should work on even the fanciest of LCD / Plasma TVs.

Bryce.

[Zyphon]

Well if you can solder two wires together, then making your own is a lot cheaper. All the instructions are on the Wiki (several versions): TV SCART cable - CPCWiki - The Ultimate Amstrad CPC Community & Encyclopedia!
I would suggest using my "Alternative" version, because it doesn't involve batteries and should work on even the fanciest of LCD / Plasma TVs.

Bryce.

Excellent! Thanks Byce. I must admit I did look at this page when I first found out about this site and out of all the methods I was leaning towards the "Alternative" version. This version seemed for me the best and most practical.

Thanks for sharing this method with the community I have already ordered some DIN plugs on eBay and as soon as they turn up I shall rip up an old scart lead. I need to buy the 3.5mm stereo socket though.

Great tutorial thanks for the link. 

[Zyphon]

@Bryce

Oh I forgot to ask. With the 100uF capacitor, is a 25v electrolytic ok?

Thanks. 

[Bryce]

Yes, it has to be electrolytic, but any voltage value from 10V upwards is fine, which is also practical, because it easily fits inside the SCART connect. But make sure you solder it the right way around.

Bryce.

[Zyphon]

Yes, it has to be electrolytic, but any voltage value from 10V upwards is fine, which is also practical, because it easily fits inside the SCART connect. But make sure you solder it the right way around.

Bryce.

Thanks for the tips. 

Ater this, the next on my list of items to purchase is a HxC Floppy Emulator, I've seen them in action on YouTube and work with a multitude of computers.

Thanks again.

[Bryce]

The HxC is a must. Especially if you happen to own a Spectrum +3 or any Amiga or other compatible computers. I have a HxC with multi-cable, that can connect to the CPC, CPC Plus or Spectrum using just one cable

Bryce.

[Zyphon]

The HxC is a must. Especially if you happen to own a Spectrum +3 or any Amiga or other compatible computers. I have a HxC with multi-cable, that can connect to the CPC, CPC Plus or Spectrum using just one cable

Bryce.

I have all of the above computers  So this device would really be useful for me. 

Yeah I was looking at the version in the black case. I don't like the version with the exposed motherboard and I don't want to butcher any of my computers in to install it internally.

Where can you get the multi-cable? That would make life easier connecting it to my various computers.

[Bryce]

I made it myself, but I can upload some instructions and a picture later if you like.

On my Amiga (600) I decided to install one internally, with the SD card poking out the original floppy slot. The CPC/Spectrum one is external, but I just bought the bare PCB version and made the box myself. You can see it here in this post: Keeping it retro (A HxC Mod)

Bryce.

[Zyphon]

I made it myself, but I can upload some instructions and a picture later if you like.

On my Amiga (600) I decided to install one internally, with the SD card poking out the original floppy slot. The CPC/Spectrum one is external, but I just bought the bare PCB version and made the box myself. You can see it here in this post: Keeping it retro (A HxC Mod)

Bryce.

That would be cool if you could upload some instructions, I would really appreciate that.

Thanks for the link, I checked it out that looks awesome. Great work.  I love projects like this.

[Bryce]

Hi Zyphon,
      here's the connection information for the Floppy/HxC multi-cable. I'll upload it to the Wiki too. It should be pretty much self explanitory.

Bryce.

(Sorry about my lack of Powerpoint skills )

Edit: I've uploaded the picure here too: DIY:Floppy Drives - CPCWiki - The Ultimate Amstrad CPC Community & Encyclopedia!

[Zyphon]

Hi Bryce,

Sorry for my late response I've have had a couple of busy days and no real time to post an adequate reply.

Thank you for much for adding this tutorial to the CPC Wiki page and for attaching the image on this thread.

This tutorial looks fantastic and I will definitely do this once I purchase the floppy emulator. I am going to buy the cased version. I know it is a bit more expensive but it does look neat in the black case.

I have ordered the components to do your Scart lead mod. I have the 6-pin male sockets. I am just waiting for the capacitors and the 3.5mm stereo lead.

I will post an update once I have made it.

Thanks again for great tutorials. 

EDIT: Do you know where I can buy the floppy connectors to attach to the floppy cable?

[beaker]

I have the one in the black box and works pretty well. The only complaint I would have is if you're just relying on the LCD for disk selection the location and angle of the LCD makes it hard to read, especially when the text scrolls and looks blurred. It would have been better designing it like Bryce's modded box with the LCD facing you. Otherwise it's only marginally wider than the disk drive housing on the 6128 and the black case is only slightly darker than the original CPC so doesn't look too out of place.

[Bryce]

Hi Zyphon,
      when I make those Floppy cables I usually use an old PC Floppy cable, the header connector and the edge for the Spectrum are already connected where they should be. The 36way Centronics connector should be easy to get from Maplin or whatever your preferred local component supplier is.

Bryce.

[beaker]

Hi Zyphon,

Are you planning to use the HxC with your CPC 464? If so, did you see this thread? HxC Floppy sd emu for cpc464