I also repair some Spectrum that people gave me to see why they didn't work. Today, It's not posible to repair a ULA fault but it's posible to repair a Z-80, memory, transistor fault, etc, etc.

Found cases



  Model Bug Repair Solution
divIDE Spectrum started like divIDE was not connected. Spectrum didn't show divIDE screen and also NMI button didn't work. Yes GAL A fault. Changed by a new one GAL22V10.
Electronica CIP-03 Romanian spectrum 48k. It started with a black screen with some vertical lines.Touching RAM chips, the screen changes and showed a lot of colour blocks. Yes This clon only have one RAM bank made by 4164 chip.Changed two chips.
Sinclair QL Ql started with white screen (normally it was ram fault). With minerva ROM the Ql showed RAM fault at chip two (see photo) but the ram chips were fine. Yes IC21 74LS245 fault.
Spectrum 48K It started with normal screen but it had some cyan pixels. The message "1982 sinclair research" was corrupted. Yes Lower memory fault. Changed IC10, 4116 chip with a new one.
Spectrum 48K At start, the screen showed a white border, cyan paper and a tiny black line of pixel in the middle of the screen. Yes Lower memory fault. Changed IC10, 4116 chip with a new one.
Spectrum 48K It start, clear the screen but it hang and show white border and black paper. Yes Upper memory fault.Changed a 4532 chip (32Kx1) to new 4164 (64Kx1).
Spectrum 48K The screen showed a lot of colour pixel (there weren't anyone flash pixel). Yes Z-80 faulty
  Spectrum 48K It works but fail when load programs. yes Upper memory fault. Changed a 4532 chip (32Kx1) to new 4164 (64Kx1).
Spectrum 48K issue 2 Spectrum works but the screen is too yellow. It also shows a lot of interferences when spectrum warm up (ULA and 7805 warm up a lot in this spectrum model).
Power connector doesn't make good contact and fails. TR4 burns during testing because this problem.
yes Yellow colour: Adjusts white colour playing potentiometers VR1 and VR2.
False contacts: Change power connector with a new one.
Interference: Checked all electrolytic capacitors. C50 is damaged. C44 is changed because is some ripple in +12VA of LM1889. It doesn't solve the problem. Finally I discover that all electrolytic capacitors near of 7805 (C27,C46) fail when 7805 warm up. Diode D11 is also changed. Spectrum run very well.
  Spectrum 48K issue 3 After TR4 changing (there weren't -5v & +12v), the spectrum started well. Some tests working well but the spectrum didn't work properly. It hung / reset when It loaded games and also with some external interfaces. I check ULA (OK),Z-80 (OK) ,ROM (OK) y TR6 (OK). This spectrum is an 16K upgraded to 48K. In the service manual said that IC25,IC26 can't be National Semiconducter chips but this spectrum had national chips. yes Changed IC25 & IC26 74LS157 National chip for 74LS157 Texas.
Spectrum 48K issue 3B Spectrum issue 3B expanded to 48K with 4532-15 chips. This Spectrum had a previous failure and many 4116 chips were changed. It resets constantly and changes from white border and black paper to white screen and black dots. Yes Multiple faults. Changed: Four 4116-3 ram chips (one broken) by 4116-2 chips. One 4532-15 and one 4532-20 chips by 4164-15 chips. IC24 chip 74LS00 broken. 180pf C64 capacitor for a new 100pF(because the upper ram is 150 ns). New C25 capacitor (improve image quality).
Spectrum 48K issue 3B Many problem:
1) No power.
2) Doesn't start, no -5V.
3) No sound.
Yes 1)7805 was damaged.
2)TR4 fails. Changed ZTX650 is changed bya a ZTX651.
3)TR7 was fine but the diode D9 was broken. Changed 1N4148.
Spectrum 48K issue 3B It starts well but when we load any game, Spectrum always gives "tape error loading" at the end. This happens with a cassette tape and using DIVIDE interface. Yes This Spectrum was a 16K upgrade to 48K with 7 OKI 3732L-20 and a 3732H-20 chips. You can not mix H and L ram chips. Changed OKI3732H-20 with a 3732L-20 chip.
Spectrum 48K issue 4S At start, the screen showed a white border, black paper and many white dot line. Yes Lower memory fault. Changed IC6, 4116 chip with a new one.
Spectrum 48K issue 4S It starts well but the screen show a pair of black pixels. Touching any key, the spectrum hangs showing a black stripe on the bottom of the screen. Some RAM memory test says it's okay. Z80, IC3, and IC4 chips are OK. Yes Lower memory fault. Changed IC13, 4116 chip with a new one.
Spectrum 48K issue 6 At start, the screen showed vertical black and white lines. There were also some pixels across the screen. With red border, there was a lot of noise. Yes RAM test showed problems in low memory. I tested some chips but there were ok. I tested PCF1306P, ROM y Z-80 chips but there also were ok.Finally, I found that the scope showed some ac signal in the +12v. C44 capacitor was not working well.
After C44 changed, Spectrum started well. I decided to change some electrolytic capacitors. Now the Spectrum has very good image and low noise.
Spectrum +48K At start, the screen was alwash black (except a tiny white vertical lines). If I pressed reset then the screen changed but alwash black. Yes -5V and +12V line fault.Changed TR4 transistor ZTX650 by a new ZTX651.
Spectrum +48K At start, the screen showed white border and black paper with vertical lines. Yes Lower memory fault. Changed IC6 and IC9 4116 chips.
Spectrum +48K issue 3 At start, the sreen showed a black screen with some garbage vertical lines and a tiny dots. Test said that this spectrum had strange lower ram problems. Yes Before test ram chips, I tested IC3 & IC4 (74LS157) chips. One of then was broken.
Spectrum +48K issue 6 1) At start the screen showed white, black and some red vertical lines.
2) A spare 4116 ram chip burned, very noise screen, unstable voltages.
Yes 1)Lower memory fault. Changed IC9 and IC10 4116 chips.
2)Tested TR4 and TR5 (OK). Changed all electrolytic capacitors.
  Spectrum+128K It started but no there was no picture on TV.
It didn't start correctly (many pixel color on TV).
yes
yes
+12V fault. TEA2000 didn't have VCC. Changed TR4 (ZTX651) and TR5 (BC557).
Z-80 faulty.
Spectrum+128K issue 2.0 No power ON yes
No original power supply with only 500mA.
78S05 regulator fault.
Spectrum+128K issue 2.0 It always showed the same image. Using a interface with its own rom, the spectrum worked well. yes
Changed original EPROM with a new one.
Spectrum+128K issue 2.1 This spectrum had a important reparation. The cables came loose and caused a short circuit. Si 1) The screen didn't change after press reset. z-80 faulty.
2) The screen change a bit but it was very similar. PCF1306P faulty.
3) Memory fault. Changed one 4164 chip.
Spectrum+2 It started but there was a power supply problem ( I can see it on TV).
It didn't start correctly (pixel color and black vertical lines on TV).
yes
yes
78S05 regulator fault.
RAM IC 18 fault.
Spectrum+2 Many problem:
1) No power on.
2) No TV image. No +12v.
3) Very bad RF image. Compositive video OK.
Yes 1) 78S05 regulator fault.
2) TR9 transistor fault. Changed TR9 ZTX650 by a new ZTX651.
3) Modulator fault. Re-soldered the resistor that join PCB and RCA connector.
Spectrum+2 Erratic behavior. Sometimes it worked but most times it didn't. Sometimes it tried to start in 48K mode. Memory tests gave messages of upper RAM banks fault but It can not identify the damaged chip. Yes Ram memory fault.
Changed IC22.
Spectrum+2A At start, the screen was black with white border. If we pressed reset button, the border changed between white and black. yes Ram memory fault.
Changed IC 3 and IC 4.
Spectrum+2B At start, the screen was black with white border. Sometime moving colours pixels appear. yes Rom Fault.
Changed IC 8.
Spectrum+2B At start, the screen was black with white border. If we pressed reset button, the border changed between white and black. yes Ram memory fault.
Changed IC 3 and IC 4.
Spectrum+2B The screen showed a lot of colour pixel. If we pressed reset button, the screen didn't change. Yes Ram memory fault.
Changed IC 5 and IC6.
Spectrum+2B The screen showed a lot of colour pixel. Yes Z-80 faulty.
  Spectrum+2B The screen showed a completed black screen. Some RAM chip were very hot.
It still didn't work. Z-80 was fine.
Yes

Yes
Ram memory fault. Changed all ram chips.
Rom A fault. Someone got out the rom and when he put it back, he bent a pin.I repaired the bent pin.
  Spectrum +3 Not power ON.
It started but there was always the same picture on TV.
Yes
No
Power supply fault.
Fault ULA.
Spectrum ZX81 The image on TV is very dark. It's necesary to put the TV bright very high to see that ZX81 is working No The ULA wasn't broken. Some early ZX81 ULA version didn't make good video signal.
  Spectrum ZX81 White image without cursor Yes Changed TR2 (ZTX313) with a new 2N2369 transistor.

Timex FDD3 When power on, disk driver try to read the disk but it stops at few second. Yes RAM memory problem. This FDD has 16K RAM made by 4116 RAM Chips.Changed one 4116 Chip.

Timex FDD3000 it started but disk driver didn't work and alwash had led on. Yes +12v fault. I changed 7812.
Timex TC2068 It started but there wasn't "1983 TIMEX..." (It started correctly with external ROM cartridge).
Badly picture color on TV.
yes
yes
ROM fault. It changed the two ROM.
Fault capacitor around video circuit.

Timex TC2068 At power up, the timex showed black screen. With the scope, I detected that there were no activity in most Z-80 pins Yes Z-80 faulty

Timex TS2068 No power on.
It doesn't start
Strange colours.
Yes
Yes
Yes
No +5v. 78S40 changed
No +12v. 78L12 changed
TS2068 can be modificated to change original ROM by EPROMs.This TS2068 had this modifications but It still had ROMs. I remove this modifications and It works.
Adjust VR2 and VR3 resistors.

Timex TS2068 No power on. +5v power supply only gives +3v
No TV image. No +12v
It still doesn't start
Yes
Yes
Yes
2 RAM chips 4416 warm a lot. I desolder these 2 RAM chips and TS2068 gives +5v.
78L12 changed.
I desolder and test the rest of RAM chips. There were 2 more broken.