Back to Life.. almost..from dead to no audio and a faulty RAM

[bola_dor]

Ok Here is the thing..
I am new to Spectrum.. but a CZ1000 guy since 14 years old..
CZ1000 are argentinian rebranded TS1000, the only difference is a sticker covering the Timex TS1000 painting with one reading Czerweny CZ1000 and they are PAL-n (same 50Hz that PAL-b in case of BW).
Ok the Spectrum: this is a CZ2000.. a Portugal Timex made hardware assembled in Argentina, with a ISSUE 6A board (48Kb ofcourse) and a a PAL-b video output in a black plastic case like that of the TS1500 and the same rubber keyboard with the metal plate as the Sinclair Spectrum...
I've got this completely dead. No video.. and the -5v and 12v rails dead... I've made a complete electrolytic recap (cheap black radials, ).. nothing new.. then I changed Tr4 and Tr5.. and did the composite mod with a capacitor... Luckily the low ram was not dead.. and it opened her eyes to life again..
keyboard membrane tapes were broken so I managed to fix them.. (will ask for a replacement later).. and the loud speaker is not beeping.. (good news is that if I plug the mic to my notebook I can hear the typing.. so tomorrow I will change TR7 and perhaps D9..

I have lot of trouble loading programs but that's not a surprise.. I think I need an amplifier...

I tried the https://github.com/brendanalford/zx-dia ... Tape-Tests sadly it didn't pass the checksum returning to BASIC with a " 4 Out of memory "
I tried several times with always the same results..
So I Have a faulty memory between 25000-32767 .
I think I will replace e all the low RAM 4116 using 4164 that are more reliable and will cost me about 4£ from China the lot of 20... ( I have a CZ/TZ1016 RAMPACK to repair to)..

Note the TR4 replacement I used.. its ratings are lower than the original ZTX650 and had to cross its legs (with the red insulator) but I couldn't find any of the regular equivalents near here.. so far it seems working OK...

[bola_dor]

I can't found a good proven replacement for TR7 about the loud speaker..
I wonder if the C635 I used to replace TR4 would work?
I don't even know if it will last as TR4..
I had to cross its leads but gave me 12V rail up again..

Another question is if this replacement can be the cause of bad quality video even I 've made a composite mod with a capacitor.. I have some gosting in borders of colors and dark pixel mainly.. "m" or "w" looks like pasted and "u" looks like "ü" as examples..
Thanks you all...

[1024MAK]

I can't found a good proven replacement for TR7 about the loud speaker..
I wonder if the C635 I used to replace TR4 would work?
I don't even know if it will last as TR4..
I had to cross its leads but gave me 12V rail up again..

Another question is if this replacement can be the cause of bad quality video even I 've made a composite mod with a capacitor.. I have some gosting in borders of colors and dark pixel mainly.. "m" or "w" looks like pasted and "u" looks like "ü" as examples..
Thanks you all...

Hi

The NPN transistor for TR7 is not particularly critical. And general purpose ‘audio’ transistor that can handle a collector current of 150mA, is rated for 1W power, and which has a reasonable gain (hFE) should be okay. Ideally with a hFE of greater than 50. The BC635 when used at audio frequencies looks to be okay for use in position TR7.

Once you replace the 4116 DRAM chips with 4164 DRAM chips, this will considerably reduce the strain on TR4. Then a BC635 should be okay in this position.

In terms of the quality of the video picture, due to design limitations, you will always get colour bleed where certain colours meet horizontally. Be it the vertical border lines or vertical lines within the normal display area.

I’m not sure about your other video problem. Can you please post a photo showing the problem.

Mark

[bola_dor]

I can't found a good proven replacement for TR7 about the loud speaker..
I wonder if the C635 I used to replace TR4 would work?
I don't even know if it will last as TR4..
I had to cross its leads but gave me 12V rail up again..

Another question is if this replacement can be the cause of bad quality video even I 've made a composite mod with a capacitor.. I have some gosting in borders of colors and dark pixel mainly.. "m" or "w" looks like pasted and "u" looks like "ü" as examples..
Thanks you all...

Hi

The NPN transistor for TR7 is not particularly critical. And general purpose ‘audio’ transistor that can handle a collector current of 150mA, is rated for 1W power, and which has a reasonable gain (hFE) should be okay. Ideally with a hFE of greater than 50. The BC635 when used at audio frequencies looks to be okay for use in position TR7.

Once you replace the 4116 DRAM chips with 4164 DRAM chips, this will considerably reduce the strain on TR4. Then a BC635 should be okay in this position.

In terms of the quality of the video picture, due to design limitations, you will always get colour bleed where certain colours meet horizontally. Be it the vertical border lines or vertical lines within the normal display area.

I’m not sure about your other video problem. Can you please post a photo showing the problem.

Mark

Hi Mark, thanks for your your replay.. Fortunately now the little machine is working quite well.. sound is playing good now.. I 've uploaded a video to show what kind of artifacts you can see. May be is part of the same "bleeding". I am using a switching PSU so that may be a cause too.. I 've made a video cable using coaxial I've got from an old MRI machine body coil (it is a big antenna) (it's a very good shielded cable).. with metallic plugs (the cable is not in this pictures.. ) but image kept the same..

Memory issue may have been a program loading problem as once I could load something using a netbook I did run for a while without any problems) I know that lower memory is not being tested as hard as I wish biy I don't have any means to test from ram..
I wonder if it is not possible to move the routines and most variables to upper memory.. perhaps will have to keep some system variables low but wouldn't be more that some bytes and then test more exhaustively the lower ram ??
I do have lots of problems loading from audio.. but seems to be related to the program or the file I am using.. I mean I have some TAP or tzx files I can load without a problem but others I can't.. some I can load with OTLA.. others playing a WAV generated from TZX or TAP files.. some of then I can't find a proper volume to load .

[1024MAK]

That “smudging” of the m and w looks like an artefact caused by the TV enhancement processing system. On some TVs you can turn all the picture enhancements off. Also play with the sharpness control. Note that with some LCD TVs, they still do some image processing even with all the picture enhancements off

If you have other TVs, also try these

Most consumer audio devices including laptop computers have audio output limiting. Either to protect users against ear damage, or because they are only designed to work with earphones.

The ZX Spectrum was designed to work with mono ‘shoe box’ type cassette recorders and in the 1980s, these had an eight ohm loudspeaker. The ear output socket was from the same audio power amplifier, so they can produce a considerable volume on their ear output.

So if using a modern audio source or laptop, the volume output may be marginal. The only solution is an external amplifier. The old style powered PC speakers that have a headphone output socket are normally suitable. Or buy a audio amplifier based on a LM386 chip from eBay or similar marketplace. E.g. this one.

If the memory/system diagnostic passes, BASIC and at least some games all work fine, and there is nothing weird going on with the display, then the ‘lower’ RAM is likely to be okay.

Mark

[bola_dor]

I'm using one of those old speakers with an earphone output socket.. I don't think is a volume problem now .what I 've noticed is that some programs hangs the load a t the same point every time even if I use WAV audio made from different TAP or TZX files Even I've made new tap files from eighty one just to check the file was usable at firs. That's why I suspect a faulty memory being hit.. but is only a guess..
I can use ffmpeg to rise the volume at the wav itself just to keep amplifiers at some point less than 100%..
Is there any enhancement or equalization made by software that may help the loads?
I have the parts to make the ZX81 "scrubber duber" .. I only have to figure out how to mount it on a stripboard.. (I ve read the 16 pages thread at the zx81 hardware forum)..
My rriginal idea was to use it on my CZ/TS1000, do you think will it be usefull with spectrum?
Thanks again

[1024MAK]

The ULA used in the ZX Spectrum uses a much better input circuit design compared to the rather crude ZX81 design. So if the audio was not very good, a device like the ZX81 scrubber dubber would help. But if the audio signal is good, it’s not likely to make any significant difference.

If you are making one anyway, of course try it

Normally you should avoid any enhancement or equalisation unless you are trying to restore a WAV or similar file recorded from an actual tape.

When a tape loads, if is a BASIC program, it starts loading into the lower RAM first and continues loading at ever greater memory addresses. If the tape contains a game written in machine code, then it can load at any address. But wherever it starts, it will load at ever greater memory addresses. If a machine code game uses a custom loader rather than the loader in the ROM, then it may load into memory in a different order, and may load faster or have so called anti-copy features.

Note there are some some bad game files on the Internet. Do the games run on an emulator?

The RAM test program you have should tell you if any of the upper RAM is faulty. It can also test some of the lower RAM. If it fails to find any problems, then either there are none, or the fault is an unusual one.

Mark

[bola_dor]

The ULA used in the ZX Spectrum uses a much better input circuit design compared to the rather crude ZX81 design. So if the audio was not very good, a device like the ZX81 scrubber dubber would help. But if the audio signal is good, it’s not likely to make any significant difference.

If you are making one anyway, of course try it

Normally you should avoid any enhancement or equalisation unless you are trying to restore a WAV or similar file recorded from an actual tape.

When a tape loads, if is a BASIC program, it starts loading into the lower RAM first and continues loading at ever greater memory addresses. If the tape contains a game written in machine code, then it can load at any address. But wherever it starts, it will load at ever greater memory addresses. If a machine code game uses a custom loader rather than the loader in the ROM, then it may load into memory in a different order, and may load faster or have so called anti-copy features.

Note there are some some bad game files on the Internet. Do the games run on an emulator?

The RAM test program you have should tell you if any of the upper RAM is faulty. It can also test some of the lower RAM. If it fails to find any problems, then either there are none, or the fault is an unusual one.

Mark

Great as always...
Yes it runs on eighty one.. so.. I'll Keep testing..
Thanks a lot