Spectrum 48k Boot pattern
Re: Spectrum 48k Boot pattern
On the 4116 chips the +5v and +12v was fine, but the -5v showed a small (0.4+) voltage on all of them.
My original Sinclair transformer puts out 14v (without load) so I'll also try a modern one that is actually 9v. Is it therefore likely that the TR4 and TR5 are dead? I just have a multimeter.
My original Sinclair transformer puts out 14v (without load) so I'll also try a modern one that is actually 9v. Is it therefore likely that the TR4 and TR5 are dead? I just have a multimeter.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum 48k Boot pattern
If the issue 3B board has the updated DC/DC circuitry, then there can be no feed through of the nominal +9V, as Sinclair added an in line capacitor. In this case, using the Sinclair ZX PSU should not be a problem. Note that the Sinclair ZX PSUs are unregulated and typically do output between 13V and 16V with no load (not connected to a Spectrum).Erm wrote: ↑Wed Aug 21, 2019 2:54 pm On the 4116 chips the +5v and +12v was fine, but the -5v showed a small (0.4+) voltage on all of them.
My original Sinclair transformer puts out 14v (without load) so I'll also try a modern one that is actually 9v. Is it therefore likely that the TR4 and TR5 are dead? I just have a multimeter.
Can you please post up a photo of the right hand side of your board, that is the side where the speaker is. Then we can see if the DC/DC converter circuitry is the older design, or the later design.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Spectrum 48k Boot pattern
Certainly, here it is.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum 48k Boot pattern
Thanks for the photo.
Your issue 3B board does not have the updated/later DC/DC converter circuitry.
So it is possible that the unregulated +9V may be feeding through the coil to the +12V rail.
If the voltage on the +9V input is slightly higher than the voltage on the +12V rail, then that is likely the reason.
Meanwhile can you test the voltage across diode D11 (1N4148).
Also test the voltage across capacitor C74.
There is a board layout here
Mark
Your issue 3B board does not have the updated/later DC/DC converter circuitry.
So it is possible that the unregulated +9V may be feeding through the coil to the +12V rail.
If the voltage on the +9V input is slightly higher than the voltage on the +12V rail, then that is likely the reason.
Meanwhile can you test the voltage across diode D11 (1N4148).
Also test the voltage across capacitor C74.
There is a board layout here
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Spectrum 48k Boot pattern
Thanks so much for your time and expertise here, it's not the first time you've helped me with words of wisdom.
I think I've done this right:
On the input side of the regulator it measures 11.3v.
The 12v leg on the RAMs are about 12.3v.
Voltage measured on the anode side of D11 is -1.6v.
Voltage measured on the + side of C74 is 5.07v.
I also removed a leg from D11 and did a diode test with my multimeter. Black on cathode showed a voltage loss of 0.6v. Round the other way was a loss of about 1.6! Same story for D12, although sometimes they tested ok.
I think I've done this right:
On the input side of the regulator it measures 11.3v.
The 12v leg on the RAMs are about 12.3v.
Voltage measured on the anode side of D11 is -1.6v.
Voltage measured on the + side of C74 is 5.07v.
I also removed a leg from D11 and did a diode test with my multimeter. Black on cathode showed a voltage loss of 0.6v. Round the other way was a loss of about 1.6! Same story for D12, although sometimes they tested ok.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum 48k Boot pattern
Thanks for those results.Erm wrote: ↑Thu Aug 22, 2019 9:26 pm Thanks so much for your time and expertise here, it's not the first time you've helped me with words of wisdom.
I think I've done this right:
On the input side of the regulator it measures 11.3v.
The 12v leg on the RAMs are about 12.3v.
Voltage measured on the anode side of D11 is -1.6v.
Voltage measured on the + side of C74 is 5.07v.
I also removed a leg from D11 and did a diode test with my multimeter. Black on cathode showed a voltage loss of 0.6v. Round the other way was a loss of about 1.6! Same story for D12, although sometimes they tested ok.
So it looks like the oscillator part of the DC/DC converter is working okay, as the +12V rail is at a higher voltage than the +9V input from the PSU, so that’s good news.
By across I meant connect one meter lead/probe to one leg and the other meter lead/probe to the other leg...! But no matter There is no need to redo these by the way.
Your result for D11 shows that either C46 (1uF) is faulty or there is a problem downstream of C46. Is the resistance of R55 (56Ω) okay? If yes, then I suggest renewing C46, then if that does not help let me know.
This should be similar to the circuit on your board: Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Spectrum 48k Boot pattern
Right, well a little progress, although the screen output is unchanged.
I changed C46, R55 is spot on.
I changed C74 as a lead fell off. I also changed C61 and D11 (I currently don't have new diodes but stole one from a parts ZX81 - one of the keyboard connector diodes which have the same value written on them). I suppose I could do the same for D12. I also disconnected R54 and checked that (was fine).
Anyway, I now have a negative voltage! It's -4.3v on every lower ram chip and they stay fairly cool instead of 2 or 3 getting boiling hot as they were before. That's not enough negative volts is it! I'm just waiting for a better desoldering solution. I suppose I should now wait for that, remove the lower ram, put sockets in and then check the voltages at the board with chips removed?
I changed C46, R55 is spot on.
I changed C74 as a lead fell off. I also changed C61 and D11 (I currently don't have new diodes but stole one from a parts ZX81 - one of the keyboard connector diodes which have the same value written on them). I suppose I could do the same for D12. I also disconnected R54 and checked that (was fine).
Anyway, I now have a negative voltage! It's -4.3v on every lower ram chip and they stay fairly cool instead of 2 or 3 getting boiling hot as they were before. That's not enough negative volts is it! I'm just waiting for a better desoldering solution. I suppose I should now wait for that, remove the lower ram, put sockets in and then check the voltages at the board with chips removed?
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum 48k Boot pattern
-4.3V is correct for that version of the DC/DC converter circuitry. If you want to get it closer to -5V, you have to perform the recommended Sinclair upgrade. I’ll post full details later. But here is a list of parts required:
DC-DC CONVERTER MODIFICATION
The following new materials are required:
Diodes:
• D15 - BA157 (it may be possible to reuse the existing D15)
• D17 - BA157
• D18 - 1N4148
• D19 - BZY88C 5V1 500mW 5.1V Zener
Capacitors:
• C46 - 1uF 50V WKG 105°C Electrolytic or ceramic axial (only required on issue 1 and issue 2 boards)
• C47 - 1uF 16V WKG Electrolytic axial or ceramic axial
• C49 - 560pF ceramic axial (if not already this value)
• C74 - 4.7uF 16V WKG Electrolytic radial (if not already fitted)
• C78/C80 - 22uF 25V WKG Electrolytic axial
• C79 - 1uF 16V WKG Electrolytic axial or ceramic axial
Resistors:
• R60 - 220Ω 5%, 0.25W
• R79 - 2.2kΩ (2k2) 5%, 0.25W
Note that if you cannot get electrolytic capacitors at the stated voltage rating, it’s okay to use a capacitor with a higher voltage rating.
Mark
DC-DC CONVERTER MODIFICATION
The following new materials are required:
Diodes:
• D15 - BA157 (it may be possible to reuse the existing D15)
• D17 - BA157
• D18 - 1N4148
• D19 - BZY88C 5V1 500mW 5.1V Zener
Capacitors:
• C46 - 1uF 50V WKG 105°C Electrolytic or ceramic axial (only required on issue 1 and issue 2 boards)
• C47 - 1uF 16V WKG Electrolytic axial or ceramic axial
• C49 - 560pF ceramic axial (if not already this value)
• C74 - 4.7uF 16V WKG Electrolytic radial (if not already fitted)
• C78/C80 - 22uF 25V WKG Electrolytic axial
• C79 - 1uF 16V WKG Electrolytic axial or ceramic axial
Resistors:
• R60 - 220Ω 5%, 0.25W
• R79 - 2.2kΩ (2k2) 5%, 0.25W
Note that if you cannot get electrolytic capacitors at the stated voltage rating, it’s okay to use a capacitor with a higher voltage rating.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Spectrum 48k Boot pattern
Well that's even more encouraging then. I may well do the DC-DC mod, but first I'll wait for the new RAM and see how/if it works with that. Thanks for now.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Spectrum 48k Boot pattern
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.