Issue 4A with no colour!

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Muttley Black
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Re: Issue 4A with no colour!

Post by Muttley Black » Sun May 05, 2019 9:17 pm

Look at the video below. JoulesperCoulomb shows the way you can test transistors. He do it on Tr4 Tr5 that is for dc converter. Do the same test on TR1,TR2,TR8,TR9 and post the results here.

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Muttley Black
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Re: Issue 4A with no colour!

Post by Muttley Black » Sun May 05, 2019 9:45 pm

You change the TR1 & TR2 with BC549C just to give more brightness to your screen, am I right? If yes, that’s mean that you still got the 2x ZTX313 and they are in working order. Have you tried to put them back and see the results?
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LET REPLY$="OFF-TOPIC"

Post by Guesser » Sun May 05, 2019 9:58 pm

PRINT COMIC$="GREAT"

:)
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Re: Issue 4A with no colour!

Post by Liveinabin » Sun May 05, 2019 10:07 pm

Muttley Black wrote:
Sun May 05, 2019 9:17 pm
Look at the video below. JoulesperCoulomb shows the way you can test transistors. He do it on Tr4 Tr5 that is for dc converter. Do the same test on TR1,TR2,TR8,TR9 and post the results here.
Superb video. Thanks. I'm getting around .7v on those transistors so, according to that guide, they check out, yes?
One alarming thing. Early in that video, there is a test for the voltage regulator. Should give a reading of >100 kOhms. I get 76.
Last edited by Liveinabin on Sun May 05, 2019 10:10 pm, edited 1 time in total.
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Re: LET REPLY$="OFF-TOPIC"

Post by Liveinabin » Sun May 05, 2019 10:09 pm

Guesser wrote:
Sun May 05, 2019 9:58 pm
PRINT COMIC$="GREAT"

:)
FOR A=1 TO 10
PRINT "THANKYOU!!"
NEXT A
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Re: Issue 4A with no colour!

Post by Liveinabin » Sun May 05, 2019 10:14 pm

Muttley Black wrote:
Sun May 05, 2019 9:45 pm
You change the TR1 & TR2 with BC549C just to give more brightness to your screen, am I right? If yes, that’s mean that you still got the 2x ZTX313 and they are in working order. Have you tried to put them back and see the results?
Sorry, just spotted this. Um, no. I changed them a couple of weeks ago and stupidly didn't keep the bits. I do have 4 more unused BC549Cs and a single (new) ZTX313 but I could easily pick up more if you think it's worth try. They're not expensive :)
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Re: Issue 4A with no colour!

Post by Muttley Black » Sun May 05, 2019 10:44 pm

Basically, this video talking about some test we need to do before switch on a ZX Spectrum. Mostly because the most common problem on ZX's are the transistors TR4 /TR5 that was used on dc circuit to provide the -5volt & +12volt that 4116 lower ram need. Missing the -5 volt can easily blow away all the 4116 ram. In the other hand a faulty 4116 ram can easily blow TR4 transistor. But all this is not part of your story. Anyway, is always good to test the voltages on your ZX just to be sure about them. Pins 1,8,9,16 of any 4116 ram can give you this results. About 7805 voltage regulator, the only thing it does is to convert the (about) 9volt to 5volt.

Now about transistor test, you need to do them with your multimeter set on "diode test". See the test on the video carefully. You should post 4 measurements for every transistor.
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Re: Issue 4A with no colour!

Post by Liveinabin » Sun May 05, 2019 10:50 pm

Oh right, of course. I’ll post results tomorrow. Thanks for all of your help tonight. Sorry to take up so much of your Sunday evening 😊
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Re: Issue 4A with no colour!

Post by Liveinabin » Mon May 06, 2019 1:05 pm

Readings taken (I am learning a LOT about electronics here)
Four readings for each:

pos at base
1) neg at collector
2) neg at emitter
neg at base
3) pos at collector
4) pos at emitter

TR1 (BC549C)

0.63
0.70
1.73
1.68


TR2 (BC549C)

0.70
0.70
1.19
1.30


TR8 (BC184)

0.75
0.75
open
open


TR9 (BC184)

0.75
0.75
open
open
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Re: Issue 4A with no colour!

Post by Muttley Black » Mon May 06, 2019 8:40 pm

TR1 looks faulty to me. Cause with neg at base, you should get "open", both on collector and emitter if i am not mistaken. If you are sure that you measure TR1 as TR1 and TR2 as TR2 then replace TR1. I say that because your TR1 measurements fit more to TR2 transistor. Anyway, to be 100% sure replace both TR1 & TR2 with new BC549C transistors and tell as if the problem solved. The other transistors looks ok.

Also post your voltages just to have a picture about them. With neg probe to ground measure voltages on pins 1,8,9 and 16 from the IC6 and post them here.
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