Search found 41 matches
- Tue Jun 23, 2020 5:37 pm
- Forum: Hardware
- Topic: TS1000 RF output
- Replies: 20
- Views: 6105
Re: TS1000 RF output
What is the voltage at the emitter? If it is zero then the transistor is faulty or the ground connection of R is dry. You should be carefully with this wiring without any caps, a short at vid-out could kill the ULA.
- Tue Jun 23, 2020 5:20 pm
- Forum: Hardware
- Topic: ZX81 16K / 32K 62256 didn't work.. advice?
- Replies: 5
- Views: 8249
Re: ZX81 16K / 32K 62256 didn't work.. advice?
Pin27 has to be connected with /WR. If you just use a pull up resistor, then a writing to the RAM is impossible. My board looks as follows (no further wires on the component side, but a cut for pin 26. Pin26 has to be isolated from +5V and connected with D3 or D5 on your board. (You can permute D1, ...
- Sun May 24, 2020 10:44 pm
- Forum: Hardware
- Topic: Yet another 48K restoration (no tape loading sound on speaker)
- Replies: 7
- Views: 7701
Re: Yet another 48K restoration (no tape loading sound on speaker)
I had the same problem: No tape loading sound and no BEEP. There was even no signal at pin 28 of the ULA. The reason was a faulty ULA.
- Sat May 04, 2019 3:03 pm
- Forum: Hardware
- Topic: TS 1000 artifacts after warming up
- Replies: 14
- Views: 4381
Re: TS 1000 artifacts after warming up
Check, if the oscillator frequency (at Pin 6 CPU) is stable at 6.5MHz. Could you replace the ULA?
- Wed Aug 08, 2018 8:30 pm
- Forum: Hardware
- Topic: Help in resurrecting my ZX81
- Replies: 64
- Views: 29107
- Wed Aug 08, 2018 7:04 pm
- Forum: Hardware
- Topic: Help in resurrecting my ZX81
- Replies: 64
- Views: 29107
Re: Help in resurrecting my ZX81
Sorry, Martin,
what I said was nonsense! I have mixed it up with the ZX Spectrum scheme! You are right: The collector of Tr2 should show the clock signal, i.e. it should pulsing (or 2-3V on your multimeter in DC). The same at CPU(pin6).
what I said was nonsense! I have mixed it up with the ZX Spectrum scheme! You are right: The collector of Tr2 should show the clock signal, i.e. it should pulsing (or 2-3V on your multimeter in DC). The same at CPU(pin6).
- Wed Aug 08, 2018 5:52 pm
- Forum: Hardware
- Topic: Help in resurrecting my ZX81
- Replies: 64
- Views: 29107
Re: Help in resurrecting my ZX81
Hello Martin, you should not unsolder the socket if there is no serious reason to do so! Look to the scheme again: The amplifier of the clock is Tr3 (not Tr2) for Iss3 board. So, you should check the join between Tr3(collector) and CPU (pin 6). Tr2 is mixing the FBAS signal and has nothing to do wit...
- Tue May 23, 2017 3:25 pm
- Forum: Hardware
- Topic: Resurrecting a ZX81 - Step by step help appreciated.
- Replies: 26
- Views: 11923
Re: Resurrecting a ZX81 - Step by step help appreciated.
But would a "bad" transistor make the signal disappear after C7/R6? I will try decreasing the Y values to see if the signal is low. Yes, it would in case the Tr2 has an inner short from emitter to basis. Replace that transistor by a new one. The amplitude at the mentioned point should be at least 0...
- Mon May 22, 2017 9:35 pm
- Forum: Hardware
- Topic: Resurrecting a ZX81 - Step by step help appreciated.
- Replies: 26
- Views: 11923
Re: Resurrecting a ZX81 - Step by step help appreciated.
Check R6 for the right value with a meter. It should have 2.2kOhm and it is located between the ULA and the CPU for Iss3 boards.
- Fri Apr 28, 2017 4:19 pm
- Forum: Hardware
- Topic: Opinion poll - AY channel mixing.
- Replies: 24
- Views: 7230
Re: Opinion poll - AY channel mixing.
This is the AY-board ("Mr. X") made by Sascha: channel C is fed into channel A and B. AFAIK the 470 Ohm resistors are now 1K: http://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=464&p=29208#p29133 Siggi The shown scheme is not due to Sascha but it is a modification of a scheme done by Wilf Rigter...