Search found 16 matches
- Mon Nov 12, 2018 8:23 am
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Sorry to keep reviving this thread, but I have some new info that could help some inexperienced enthusiasts. I found why it was only 4.7v on the RAM chips... Because I needed to verify first the voltage regulator, in all these tryouts I used some breadboard cables jumpers that seemed to drastically ...
- Sun Nov 11, 2018 8:41 am
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
I found out from the datasheet that the installed RAM (M3764) actually permits a minimum recommended voltage of 4.5 to 5.5 - and supports spikes of 7v (but for short time) maybe that explains why is still working. Maybe will help others this info if they will encounter the same problem.
- Thu Nov 08, 2018 8:30 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Say no more, it works! I just put a TIP31C in place of the ZTX653 (TR9) - ok I may overdo it with that radiator improvisation, but it was for testing :D RAM seems to have those 4.7v - 4.72v but it seems it works like that. TEA2000 has around 10.5v or something After 15 minutes these are the approxim...
- Wed Nov 07, 2018 9:22 am
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
This method gets increasingly impractical as the current increases in a design. As more power is lost in the resistor, and you also have the problem of the voltage ‘lost’ across the resistor means that the circuit that is being supplied no longer sees the correct supply voltage. I just read this ag...
- Tue Nov 06, 2018 11:26 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Ok, so I tried with some primitive PSUs only for the 5v line. I connected the positive terminal from the power source to the positive pin of the voltage regulator output, and the negative to the negative pin nearby. I observed that I have some massive voltage drop - somewhere like 4.1v are reaching ...
- Tue Nov 06, 2018 9:00 am
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Following the post above,
TR4 seems to work... Maybe I should try pumping 12v + 120 Ohm (0.1A) resistor to the D20 diode and check some voltages? Do you have some advice what voltages should I check first to spot this cursed short?
TR4 seems to work... Maybe I should try pumping 12v + 120 Ohm (0.1A) resistor to the D20 diode and check some voltages? Do you have some advice what voltages should I check first to spot this cursed short?
- Mon Nov 05, 2018 4:13 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Thank you very much for your answer... Sorry for asking all these questions that the answer can be pretty obvious for an experimented person. Is clearly making some light in the understanding of how these circuits work and hope that will also help others. So basically I could first try checking if T...
- Mon Nov 05, 2018 10:53 am
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Oh, by the way, to reduce stress on the PCB, when removing a component where you are not intending on reusing it (such as an electrolytic capacitor), it’s better to note down the holes it uses and the polarity (or take photos), then cut it’s legs, then desolder the legs, then fit the new one. Mark ...
- Wed Oct 31, 2018 3:59 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Electrolytic capacitors can cause all sorts of problems. If you are good at soldering and desoldering, you should indeed replace any that look like they are leaking, or may leak. Mark Hey Mark, Thank you for the reply, can you please tell me if the steps from this previous post: https://spectrumcom...
- Tue Oct 30, 2018 10:08 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
In the meantime I tested the coil resistance: Primary winding (connected to the transistor collector) 0.05 ohms. Secondary winding (connected to the transistor base) 0.05 ohms. Primary winding to secondary winding: greater than 20M ohms (it kept growing, 20M is maximum on my multimeter) Do you think...
- Mon Oct 29, 2018 1:22 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
The 7805 voltage regulator supplies the +5V Rail. If the voltage on the input to the 7805 voltage regulator is at least 7.5V, then the output should be within +5V +/-5% at worst. So 4.75V to 5.25V. Most 7805 voltage regulators manage better than +/-5% though. If the regulator and it’s heatsink are ...
- Sun Oct 28, 2018 7:41 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Hey Mark, thank you for your replies I checked the R79 and R78 outside circuit and indeed they are good, thank you for the tip! R78 is correct at least on my board - and is indeed connected with C27 TR9 can be burned if is reversed (sorry my noobines)? I initially intalled it with the emitter on the...
- Sun Oct 28, 2018 4:05 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Think that I found R52, it has continuity with D19 and I think is the one.. The thing is that I'm reading seomething like 10k value on it (on circuit), and the colors doesn't seem to match the color charts - it has a gold band but it should be brown so to be 2.2k ? And the Tolerance band is black, b...
- Sun Oct 28, 2018 3:16 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Thank you for your reply, Mark! Is there any way to test the coil? Visually it look fine ... I was wondering, is possible that a resistor to allow this failure of the transistor? I checked on circuit the R79 transistor and I have no reading on it - I also checked R54, R55, R30,R78 and these have som...
- Sat Oct 27, 2018 10:08 pm
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122
Re: ZX Spectrum +2 booting problem
Hey thank you for the reply! Seemed that the voltage regulator went crazy... I had more than 5v in the output. I tried with another one, voltages are correct now, but... :D I also observed that I have only 4.72V on the ram chips from the right side of PCB and 4.69v in the far left side. The TEA2000 ...
- Mon Oct 22, 2018 10:11 am
- Forum: Hardware
- Topic: ZX Spectrum +2 booting problem
- Replies: 30
- Views: 7122