Sinclair ZX80 / ZX81 / Z88 Forums

Do you mean a professional repairer?

Mark

1024MAK wrote: ↑Fri Mar 06, 2020 8:13 pm
Also with the machine switched off / disconnected from power, test pin 2 to 14, and then pin 2 to the power rails: +5V, +12V, -5V and 0V. Then compare with pin 2 on the other lower RAM DRAM chips. If you get any unusual results, post up your findings.

Mark

"Test" how? Resistance? Continuity? What results should I spect..
(I am on an issue 2 TS1016 rampack now)

bola_dor wrote: ↑Mon Mar 16, 2020 1:06 am

1024MAK wrote: ↑Fri Mar 06, 2020 8:13 pm
Also with the machine switched off / disconnected from power, test pin 2 to 14, and then pin 2 to the power rails: +5V, +12V, -5V and 0V. Then compare with pin 2 on the other lower RAM DRAM chips. If you get any unusual results, post up your findings.

Mark

"Test" how? Resistance? Continuity? What results should I spect..
(I am on an issue 2 TS1016 rampack now)

Resistance. Pin 2 to pin 14 should be zero Ω or nearly zero Ω.
The other results should all be greater than 5kΩ.

Mark

1024MAK wrote: ↑Tue Mar 17, 2020 3:28 pm Resistance. Pin 2 to pin 14 should be zero Ω or nearly zero Ω.
The other results should all be greater than 5kΩ.

Mark

They are ok then.. I posted here.. viewtopic.php?f=7&t=3606&sid=e38b8fa285 ... e9345e11fd

1024MAK wrote: ↑Sat Mar 14, 2020 10:02 pm Do you mean a professional repairer?

Mark

Pro or not. Anyone who has sufficient electronic knowledges to repair a Spectrum (in fact, I have two Spectrum to repair).
This afternoon I will try to replace TR3 as I have read somewhere that it is also involved in the RAM function.
I have also a TR6 on my Z80 (issue 2 motherboard), TR6 is there to correct a bug on ULA, so it should not be involved in my RAM problem, but I am wondering anyway ...

TR3 supplies the clock signal to the Z80. If TR3 is defective, the Z80 will do absolutely nothing and the machine will fail to start up (but you will get a screen of random colours and random pixels as the ULA may still be working).

I’ll point you in the direction of professional repairers later.

Mark

Mark, thanks a lot for your TR3 information.
Because of Covid19 I will not send my Spectrum's for repair before 4 or 5 months ... So before that I would like to try all I can to fix them.
I will soon (I hope) receive a new small oscilloscope. This one :
https://www.amazon.fr/gp/product/B077CZ ... U1VE1O4ZFQ

I never used any oscilloscope, so I will train myself to use it when received.
Will you be able to explain me how to use it to try test some components of my Spectrum ?

This "Oscilloscope" is no use for Sinclair stuff because its limited to 200khz.
Thats good for Audiosignals, but as the Sinclair oszillators are about 7 MHz the needed Oscilloscope will be twice of that (15MHz) at least. 20MHz analogue is ok for that. That is the usable frequency, not the sample rate. Sample rate in digital oscilloscopes need (again) be twice (better 5 times) the usage frequency (30megasample/second).
Its always good to go a little higher, so sample rates of 40megasample/second will be fine.
Examples are:
MongKok DSO168 or better Dastrues Digital Mini Oscilloscope 2.4 Inch https://www.amazon.fr/Oscilloscope-mini ... ljaz10cnVl
when staying with Amazon

Thanks a lot for your quick answer, I will check that.
EDIT : AAaargh ! it's much more expensive ... As I do not know if I'll be able to use it in other cases than for the Spectrum ... I need to think about it ...

Do you have a 4020B or a 4060B CMOS Logic chip?

Mark