Hello,
This morning I tried a recent find, a tall keys CPC 464. I am using a Mean Well 5V/3A PSU and use a SCART cable to connect the CPC to my TV. The PSU work well with another CPC.
So far so good, the CPC 464 power up, then I tried to load a game with the tape drive. The screen started to shake vertically (seems like off-sync issue effect). As nothing more happened, I stopped the tape drive, the computer was frown. Then I saw this little handmade switch on the top left of the keyboard... I tried to flip it, assuming it was some sort of reset mod, nothing happened. then I tried to reset using the power switch, and the CPC does not power up at all, not even the red light :( .
Seeing the picture of the switch modification, do you have any idea of what purpose it serve ? Flipping this thing could have fry the whole computer ?
Check that the powerswitch still works, these tend to fail eventually and may need to be taken apart and cleaned.
EDIT: Switch looks like some printer port 8bit hack, so should not be a problem.
Thanks you Duke, I bridged the power switch and the CPC boot again. After a good clean, everything is fine :) 8 bits printer hack ? I will let it wired as long as it is harmless to the CPC.
Yeah, there's no harm in it, especially if you never actually connect a printer :)
Hello again,
On this CPC any action on the tape deck result in a freeze with graphical artifacts. I tested my tape on another CPC 464 and it load just fine.I supposed the freeze on game loading could be related to faulty memory chips, but even rewind a tape result in a freeze. Maybe a shortage somewhere ? I didn't find much or maybe do not use the correct keywords related to tape drive issues. Does anyone experienced this with a CPC 464 ?
Nope, if any RAM was bad the 464 wouldn't boot at all. More likely:
- A short in the tapedeck.
- Bad capacitors.
- Dodgy connection (the power switch is fed via the tapedeck connector).
Bryce.
Thank you for the leads Bryce.
I have not seen any blown capacitors on the tapedeck PCB. There is some sort of orange/pink glue on few components (resistors and capacitors) but it does not look like it leaked from any of them.I will investigate with my multimeter then !
Check that none of the loose wires have been caught under any of the screws or damaged on any sharp metal edges. The orange stuff hasn't leaked from anything, it's meant to be there.
Bryce.
Well, there is nothing loose or shorted on the tapedeck. Using the multimeter I mesured 5.00 V to the power input when the CPC is off, and it drop to 3.96 when the CPC is on. No chips seem fried as they stay relatively cool after few minutes idling.
3 capacitors on the motherboard are black on the top, as you can see on the picture. When I touch them with my multimeter, it reproduce the graphical scramble behaviour. Does it seems to be a good lead ?
They are ceramic capacitors and definitely won't be the issue. The electrolytic capacitors (That blue can at the back of you picture with 10V 47µf written on it) are the ones that cause issues. However, if the voltage is dropping to 3.96V there is definitely a problem somewhere. It should never drop below 4.75V. What powersupply are you using.
Bryce.
A quick check if the board is OK is to take out all tape deck assembly - power the 464 board only, by removing the tape deck completely, pull the molex connector. Just "short" the switch molex pins so that the board will get power and turn on. I forgot which molex pins go to the power switch, but it is easy to find from the schematics. Just short them out.
That way you can immediately check if it is the tape assembly unit. You only need one bridge wire for the molex pins on the board (or alligator clips or the like). But careful to not short other pins...
I am using a Mean Well 5v/3A PSU. As it is working well with a cpc 6128 and another cpc 464, the issue seems to be on the CPC side. Thanks for the advice, I will try to bypass the tape deck and check the voltage in this configuration.
This is a picture of my "bypass tape deck assembly" MOLEX test connector. See, wires 1 and 3 (going to the right in the picture) are bridged. Plug that into your 464 and power it up (board only).
Voltage measured without tape deck : 4.50V. I will see if I found a capacitor similar to the blue can one in order to replace it.
What does that mean? Without tape assembly unit you are not getting a picture either?
OK, great - then you have diagnosed the bug to be either the PSU or the motherboard.
Quote from: Liartes on 20:31, 12 August 20
Voltage measured without tape deck : 4.50V. I will see if I found a capacitor similar to the blue can one in order to replace it.
Have you cleaned the power socket contacts?
Bryce.
You were right, issue was power related...
I recycled a power cord from a noname PSU. The wires were too small and they can't follow up the power to feed.
I tried with the 12V power cord scrapped from my CPC 6128 : 4.92V when the computer is on.
My other CPC worked because they were in their tolerance margin, but this CPC 464 was just a bit too underpowered to keep on.
It is running fine now, Thank you so much for your advices. Beside this one, my whole collection will benefit this !
With the added advantage that your house also won't burn down! Did you not notice how hot the cable was getting?
Bryce.
Not at all, longplay sessions are on my GX4000. I am building a MP-like box with power-supply and scart-to-HDMI converter combined. As I used the computers for short test sessions only, I didn't notice anything !
The wire would have been disappating around 2W and would have been getting relatively hot very quickly (especially when the motor was running). It's not enough to melt the insulation, but it would have been noticable if you were holding the wire.
Bryce.
Quote from: Bryce on 15:09, 13 August 20
The wire would have been disappating around 2W and would have been getting relatively hot very quickly (especially when the motor was running). It's not enough to melt the insulation, but it would have been noticable if you were holding the wire.
Bryce.
A 464 consume between 0.8A to 1.2A. A voltage drop of (5.0-4.5V) would be in the range of 0.5*0.8 = 0.4W to 0.5*1.2 = 0.6W.
How do you get to 2W ?
I was using worst case calculations: He was using a Meanwell PSU which outputs around 5.2V on the 5V rail and said he measured 3.96V on the input, so a drop of 1.24V. The CPC is old you can assume that the motors / capacitors etc could bring the current up to around 1.5A (worst case) = 1.86W.
Bryce.