CPC464 LED on, no output

Velociraptor · 21:25, 15 July 19

The 464 I bought on ebay seemed to be in reasonable condition. However having now tried it and then taken apart and cleaned a few areas with iso it seems that a mug of coffe or coke has been spilt on it. There's brown stains that came off. I've cleaned the board as much as I can but the outcome remains the same. I now also have a 6128 and it works fine with the same power/video output connections.

Power on - LED shows. No beeps. No signal at all to the screen. Removing and reseating the Z80 has no impact. Same for the 400008 gate array.

Leaving the power on for 10 minutes results in no warm chips apart from the gate array, and I did not have the heatsink back on it.

There does appear to be a damaged trace on the rear of the board but a continuity test with a multimeter shows continuity.

I've ordered a Z80 and some RAM chips on ebay in case swapping those out helps.

I'm looking for any advice on what to start looking into next.

Here's some images in case that helps.

LED, but no image.

https://i.imgur.com/sSRFXaS.jpg

The 6128 works fine with the same wiring.

https://i.imgur.com/1Eu1oTm.jpg

Back of the board showing stains.

https://i.imgur.com/R6M9W9N.jpg

Front of board

https://i.imgur.com/HX29Ea3.jpg

The white stuff on the Z80 is I think the thermal paste that's under the gate array, the thermal paste was not dried out which surprised me.

A closer shot of the Z80

https://i.imgur.com/b4nvgUe.jpg

Cleaned socket

https://i.imgur.com/mZ5RsF9.jpg

You can see some grime on the cotton bud tip. This was with iso alcohol.

Filth on edge of board

https://i.imgur.com/y61dQ9T.jpg

You can see where the liquid has drained down to and stained the board, and also wicked up the screw.

Damage trace

https://i.imgur.com/nfpeYFd.jpg

There is continuity here though.

Here's some of the manky stuff coming off on a bud with iso

https://i.imgur.com/PYk2h4W.jpg

I noticed this taped on wire

https://i.imgur.com/HJmwoTr.jpg

Is that normal? It doesn't look like it should be like that?

Token · 23:40, 15 July 19

Hi
I'm not a specialist but I think the last pic with the taped on wire should be under the PLAY key. (relay switch?) Otherwise nothing on screen and no beep, you did well with RAM, even if it could be something else.

Velociraptor · 00:26, 16 July 19

I've done a bit more nosing and when I cleaned the grease off the gate array I found a bit of the brown muck between it and the heatsink. That means to me that the brown liquid had got in there before the grease was reapplied. Which makes me think someone has tried to repair this even to the point of reapplying thermal grease and reseating chips, perhaps cleaning it up a bit.

Bryce · 08:05, 16 July 19

A few points: Nobody spilt anything into it, that brown stuff is a type of PCB coating used on very early machines. Clean it off if you like, but there's no problem leaving it there either.

The "damaged" trace just missed the solder wave, it will work perfectly.

The taped switch is a problem. It should be screwed to the bottom of the tape deck frame and it's the reason the tape isn't doing anything. Try fast forward and then gently press those two metal prongs together and the motor should turn. This needs to be fixed, but the main computer needs to be fixed first.

Someone was definitely inside and couldn't repair it. It will most likely be the RAM or ROM that has failed. Does it produce any picture on the screen?

Bryce.

Velociraptor · 08:39, 16 July 19

No picture on screen at all.

https://i.imgur.com/sSRFXaS.jpg

Bryce · 09:12, 16 July 19

Ok. There's a lot to be done. What equipment do you own and how would you rate your electronics skill level?

Bryce.

Velociraptor · 09:19, 16 July 19

I have a cheap multi-meter. A crap soldering iron (that I've been off and on trying to find a decent replacement for, I've looked at a few Chinese ones but nothing has really grabbed me). I have a lot of miscellaneous soldering stuff on the way, stuff like braid, flux etc, solder wire, IC extractors, also some magnifying goggle things.

I don't have an oscilloscope but I was looking at https://www.amazon.co.uk/KKmoon-Handheld-Digital-Oscilloscope-Soldered/dp/B01HZ1Q26M/ and wondering if that would do the job.

I've only done one bit of soldering, and that was just a loose connection on something, but I've been watching loads and loads of videos recently so I'm quite keen to do something like this.

My understanding is I'll be checking continuity, checking voltages on ICs and if needed checking the oscilloscope (I'm vague on this!).

I've got the patience for it, I'm not in any rush to get it working and I like the idea of a project. I got lucky on a 6128 that's in great condition and works so it's not even as if I need to get this working to play CPC games.

Bryce · 09:29, 16 July 19

Ok. Most of the soldering you'll need to do is relatively "safe" as you should use sockets when replacing any chips. The most difficult bit is removing the old chips, so read and follow this carefully: http://www.cpcwiki.eu/index.php/IC_Repair Especially the bit about desoldering the pins from the TOP of the board. Not doing this can destroy your CPC as one user here unfortunately recently discovered.

Forget that KKMoon toy. It has a bandwidth of 200kHz, not even enough to properly display a bit change on the data bus, let alone view the CPC clock which is running 80 times faster than that scope can handle. Any scope for 15 pounds isn't going to be of any use. What's your upper limit that you could spend on a scope?

Bryce.

Velociraptor · 09:35, 16 July 19

Ah I read that guide last night about removing ICs. They can't be removed without cutting the legs off? I've seen people use hot air or a desolder station and get them off. I'm going to have a look into that board destroying thing because I didn't know that could happen and I'll need to avoid it.

Which I think means no just desoldering every IC on there and socketing everything. I'd be wrecking a chip by desoldering it so I'll only desolder dead chips and socket before putting the replacement in.

How would you do it and preserve the IC if it was one that wasn't easily replaced?

For the oscilloscope, whatever would serve me for the CPC and the ST if I need to, without wishing I'd got a "proper" one. I don't really have an upper limit, but I don't think it's something I'll use a lot.

pelrun · 09:42, 16 July 19

For the soldering iron, I cannot recommend the TS100 enough, as long as you run it off a 20-24V power supply (surplus laptop power bricks work great.)

I even recommend it over the "professional" base stations that cost a few hundred dollars, it's that good.

Bryce · 10:10, 16 July 19

Quote from: Velociraptor on 09:35, 16 July 19
Ah I read that guide last night about removing ICs. They can't be removed without cutting the legs off? I've seen people use hot air or a desolder station and get them off. I'm going to have a look into that board destroying thing because I didn't know that could happen and I'll need to avoid it.

Which I think means no just desoldering every IC on there and socketing everything. I'd be wrecking a chip by desoldering it so I'll only desolder dead chips and socket before putting the replacement in.

How would you do it and preserve the IC if it was one that wasn't easily replaced?

For the oscilloscope, whatever would serve me for the CPC and the ST if I need to, without wishing I'd got a "proper" one. I don't really have an upper limit, but I don't think it's something I'll use a lot.

Here's what happens... Not pretty: http://www.cpcwiki.eu/forum/technical-support/me-and-my-schneider-cpc-464-again/msg171427/#msg171427 Those copper tracks are only glued to the PCB and if they get too much heat or pushed away from the PCB, they will quickly float and break off, leaving you with the messy job of having to bridge all the breaks. Destroying the chip isn't an issue if you have a replacement, but destroying the PCB can be game over.

If you need to remove a chip that still works, it's a difficult process that takes quite a bit of practice. It can be done with hot air or with braid, but the chances of destroying the chip and / or from heat is very high and I wouldn't recommend it unless absolutely necessary. On a CPC it is rarely necessary, replacements are easily sourced and relatively cheap.

As for scopes, you can get a half decent USB scope for about 60 quid: https://www.ebay.co.uk/itm/Hantek-6022BE-PC-Based-48MSa-s-Car-Automotive-2CH-USB-Digital-Oscilloscope-NEW/113796575904?hash=item1a7ecdf2a0:g:P7UAAOSwmftdEZMc This is 20Mhz, which will much better serve you than that KKMoon toy and the display size is whatever your laptop has, not some postage stamp LCD. If you can spare the extra cash, there's a 50Mhz version too.
If you prefer a standalone unit, then the price will be around the 200 pound mark, but you have the freedom to use it with having a laptop with you.

@pelrun: Yes, the TS-100 is a fine device, I have one too. However, I only use it for mobile situations and the tip is a bit too long for me for everyday use.

Bryce.

Velociraptor · 10:20, 16 July 19

Hmm. I don't have a laptop other than my work laptop so I'm not sure if I'd want the USB one. Would it work with an android phone though? - Edit : Yes. Apparently there's an app. Out of time now but I'll have a look when I'm home from work.

What would you recommend for a soldering iron then? Let's say that I wanted to spend no more than £100 on it, or maybe more if it was hot air too, or was otherwise some kind of 2 in 1 thing for something else I'd need.

Bryce · 11:14, 16 July 19

No, they don't work with Android.

As for irons, it's difficult. I stick to known brands to ensure I can still get the tips I need in a few years, but I go through quite a few tips per year. There are no name brands that are ok, but I don't have much experience with them. Hakko is probably the cheapest known brand (if you can live with the blue/yellow Lego design). Just make sure that you can regulate the temperature, the tips are available as spares and that the tip is not too long.

Bryce.

Velociraptor · 20:40, 16 July 19

I have found 3rd party software which claims to work with them on Android. That aside though I think it'd be best to get this option as even without a laptop I can just use my desktop. Once I've moved house I'll have a room where everything will be so it's not important to be mobile. I shouldn't have started on the 464 until after the move but I got temped to try it out.

Where's a good place for me to find out what I need to be testing on the board to narrow down the fault?

Bryce · 07:52, 17 July 19

Quote from: Velociraptor on 20:40, 16 July 19
Where's a good place for me to find out what I need to be testing on the board to narrow down the fault?

You're already there

In a case like this, I would normally connect a LowerROM board to bypass/test the internal ROM. Once I know that works, I would run Geralds RAMTest from it to see which RAM has failed. You don't own any of these devices though, so you will have to measure things manually and that will require an oscilloscope.

Bryce.

Velociraptor · 18:42, 17 July 19

Ok. Well I move house in a month so I need stop this until I've moved. I should be spending the time packing stuff up. I didn't do this before because I felt I didn't have the space and that's the position I'm at now, so it'll wait a couple of months.

Once I've moved the CPC will have it's home on a desk and I'll be able to do what I want whenever I want without having to put it in a box afterwards.

Once I've moved I'll then work out what I need to do to it.

http://hscope.martinloren.com/

In the mean time I'll get hold of that oscilloscope and try that android app for it. Might work. Ideally it will, but I can manage if it doesn't work on android. I still have the ram chips and z80 coming so hopefully they'll be here by the time I might want to use them.

Will I need a better micrometer than the very cheap one I have? Or is there anything else that you think I should have, I now have time to wait on stuff coming from China.

Edit : So yeah I went and bought a Hantek DSO5102P so never mind that stuff

Bryce · 07:47, 18 July 19

Micrometer? You mean a Multimeter? Which one do you have at the moment?

Bryce.

Velociraptor · 15:00, 18 July 19

https://www.amazon.co.uk/dp/B00TM0W8ZY/

I went and bought a soldering iron and hot air thing too. So I think I've got what I'll need when I get to it.

https://cpc.farnell.com/duratool/d00673/soldering-station-uk-eu-plug-60w/dp/SD01385
https://cpc.farnell.com/duratool/d03329/station-hot-air-bs-plug/dp/SD01139

Bryce · 07:27, 19 July 19

The Duratool devices are fine, but don't even consider putting that multimeter anywhere near the 600V they claim on the front. It's only safe up to about 60V so I wouldn't even measure the 240V of a socket with it.

Bryce.

Velociraptor · 19:15, 20 July 19

Is there one you recommend to people? Don't worry if there isn't, I can always look around if I find a need to measure mains voltage.

Bryce · 07:50, 22 July 19

The best low-cost meter you can get is the Aneng AN8008: https://www.amazon.com/Alloet-True-RMS-Digital-Multimeter-Voltage/dp/B072JMBLJS
You can safely stick this into any socket you like

Bryce.

Velociraptor · 17:25, 22 July 19

Got one ordered, and I can't wait to jam it in my sockets.

I think/hope I've got everything I need now. I'm going to move house and ordering from China will be a pain because I don't know exactly when I'll move and when the stuff will come.

I now have the desoldering hot air thing. The soldering station. The sillyscope. Some solder. Some braid. A solder sucker. Some flux. Some single strand wire. Tip tinner. A soldering mat. Some magnifying goggles. RAM and a zilog on their way. Some ram sockets and some 40 dip sockets.

Hope I've not missed anything

Bryce · 08:06, 24 July 19

You're sorted. The only other thing required is experience, but you can't buy that, it will come with practice.

Bryce.

Velociraptor · 20:46, 24 July 19

Yeah, the 464 isn't a disaster if I completely kill it, since I have the 6128. However I'd very much like to bring it back to life and I won't be doing what happened in that thread you linked. Bizarre that he wrecked it and sent it to you, you then did that beautiful repair and it was then snapped in two on purpose. I can smell a bit of a rat there. I do wonder what happens if I put solder braid along the top of the board along the pins on an IC, and then use the hot air gun and then reposition it and repeat, finally flipping it over and seeing if I can wiggle each individual leg with a plastic spudger. Not going to do that without a good reason though. Which means I'll hopefully identify a dead chip and remove it by cutting it's little legs off one by one.

I won't touch it now until I've moved house, but once I have moved house I've no idea what I need to look at. Is there some kind of reference somewhere of where I should be looking for voltages and clocks?

Bryce · 07:52, 25 July 19

Quote from: Velociraptor on 20:46, 24 July 19
I do wonder what happens if I put solder braid along the top of the board along the pins on an IC, and then use the hot air gun and then reposition it and repeat, finally flipping it over and seeing if I can wiggle each individual leg with a plastic spudger. Not going to do that without a good reason though. Which means I'll hopefully identify a dead chip and remove it by cutting it's little legs off one by one.

I won't touch it now until I've moved house, but once I have moved house I've no idea what I need to look at. Is there some kind of reference somewhere of where I should be looking for voltages and clocks?

You can try that, but you'll discover after it takes you about 30 minutes to remove the first IC, that it's just not worth it and the chance of damaging the board is still high. There can be a lot of solder behind the pin (underneath the IC) that the braid won't have removed and is impossible to get to.

There's no real guide, just because so many things can cause problems. When you have moved and are ready to repair the PCB, come back and we can go through the options in stages.

Bryce.

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CPC464 LED on, no output