I will check C504 to see if I can get any pulses out of it.Probably the BU407 is faulty. If it is, you are lucky - it will have over 100V pulses on its collector so your scope would be dead by now!
Next guess would be C504 is open circuit.
Brian.
UPDATE I get pulses out of C504, it does not seem bad.I will check C504 to see if I can get any pulses out of it.
The scope has 250V input at 1M (max), I do not think it will find any trouble, do you?
Ok, the thing was working ok, but then some nice guy thought that it would be a brilliant idea to change some chips with ceramic versions, as well as the ROM with an EPROM. When fitted the EPROM, it was working ok, but when changed a few other logic chips it stopped working. It stopped doing the start up sound. At some point, (he does not remember if it was at the same time or afterwards), he noticed this screen problem as well (filaments not glowing).Hello neazoi,
There would be nothing wrong with Q502 (BU407), as you would be measuring R507 (4.7Ω) resistor in the circuit.
This is measuring between the base and emitter.
I also doubt that there would be anything wrong with T501. It is possible you could have shorted turns, but unlikely.
Try removing T501 from circuit, then remeasure it. If you find it OK, then you need to look elsewhere.
The filaments won't glow if the high voltage isn't working (flyback transformer (T502)).
Looks like you need to check voltages...
Please let us know how you get on.
By the way, what exactly is it's symptoms apart from the CRT not glowing?
Regards,
Relayer
I desoldered the BU407D (Q502) and checked it on a components tester. The result is short in the checker.Probably the BU407 is faulty. If it is, you are lucky - it will have over 100V pulses on its collector so your scope would be dead by now!
Next guess would be C504 is open circuit.
Brian.
As far as concern the logic board, I get no clock signal if I connect the scope to each pin of the crystal of the cpu. What does this mean?I desoldered the BU407D (Q502) and checked it on a components tester. The result is short in the checker.
I also soldered a BU508AF (from an old TV I happened to have) in place, as a quick test.
Now the filament works and I get these waveforms at it's base and collector. Note the scope values.
With about 3vpp at the base it produces 93vpp pulses at the collector.
I can hear a high pitch sound from the vectrex, it might be normal or it might be HV arcing? I can see no visible ark, but of course this is difficult to say. It might be the HF deflection I do not know. The volume is not high, but neither as low as I can remember on the old CRTs. I do not remember if the working vectrex had that sound, cause it's speaker has a lot of hum normally. Also, now I have the cabinet open, so it is heard a bit more.
I still see nothing on the screen but I can also hear no startup sound due to the faulty logic board.
Is it safe to leave this replacement transistor there for my tests, until I get the original one?
I can find these transistors locally, cheap. But thank you very much for your kind offer anyway!The BU508 is fine for testing.
I have some BU406D transistors here if you need them. They are identical to the BU407 but have a higher VCE rating.
The scan and HV seems to be working so you now need to concentrate on the logic board. If it doesn't initialize you will never get any sound or video.
Brian.
I put the 10x scope probe to each of the pins of the CPU and I get no clock or pulsed signal at any of them. I only get 0v or 5v or some voltages in between, but always DC. I tried different horizontal scope settings. On changing the CPU to 68B09 instead of 68A09, I notice a steady 5v DC on one of the cryatal pins, whereas with the A version I sense almost no DC.The clock should run regardless of any other circuitry so get that working first.
Use x10 probes on the crystal, otherwise the probes themselves may stop it oscillating.
Note that with the exception of the 555 you have already conformed is working, there are no other clock sources in the machine. This means if you see activity on the other pins, even if the crystal appears to be dead, it is almost certainly running.
Brian.
I tried 1M across the crystal but no luckHi,
Seeing DC (close to VCC or GND) on an XTAL surely means it is stopped.
The problem is: even a scope probe (with it's impedance) is able to stop an XTAL oscillator.
Thus it's more informative to measure the oscillator OUT than the IN, because it is less sensitive on load.
If the oscillator input is stopped by some leakage current on the IN node (dirt, humidity, internal currents, flux residuals...) then a 1M across the XTAL may help to start oscillation.
Also you may replace the capacitors.
Klaus
RST pin 37 on the CPU is high +5V.Again, looking at the data sheet, if -RES is above 4.0V (note this is higher than normal logic 1 threshold) there should be activity on the other pins, even if it is just searching for instructions. It is pulled high through R201 with C224 and C228 delaying it's rise at power-on. If it is lower than 4V check the component on the reset line and reset switch. Note that the reset pin on the sound generator IC is an input so it shouldn't be able to drive the reset signal.
Brian.
Thanks for that info.Hi,
what´s the exact part number of both ICs?
they may end with -P or -EP or else (While the -EP is likely not to work with your circuit, because it is not designed for XTALs)
Klaus
I fixed it!Hi,
so,
* Don´t use one with an "E" in the suffix.
* MC68A09 and MC68B09 should work(speed), but MC6809 may not work with 6MHz.
"C" means extendend temperature range (does not matter)
"P" means plastic package (does not matter)
"S" means ceramic package (does not matter)
So after power ON I´d check (in this order)
* power supply voltage
* reset level
* XTAL activity
(I think this is as you did)
Klaus
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