Repair HAMEG oscilloscope

[mpavlica]

Hello

I have HAMEG HM604 which is in mint condition. Only couple of working hours. My dad barely used it...
Anyway, I started using it, and suddenly, beam intensity is lost.
When I switch it ON, i get beam with high intensity and it is wide on X axis. After second, or two, intensity is lost and I can barely see beam. Also, beam is narrow/short on X axis, covering only center of screen, about 1cm shorter from each side.
Ive opened it up and first i checked PSU, all good, voltages are fine.
I measure on Z board volts, and there I found a problem.
When Component Tester is OFF, point where VR601/R620 and T604 are, and schematic says that it should go from 0...1.4V for DARK, i get 1.3...2.8V... And R639 voltage, that should go from +8..55V goes only up to 33V
When component tester is ON, i get 0V at emitter of T604 and +55V at R639, but beam intensity is still low.
VR601 at wiper side is OK, i get from -11,5....+11,5V so thats fine.
BIAS INTENS i can adjust to have +82V, thats okay.
When i switch lights off so i can see beam, i can regulate focus, i can see changes on a beam.

Any ideas where to move on? I am a bit lost now...
THANKS!!

73 de YU7XW
 

[WaveyDipole]

You say that VR601 seems to have the correct voltages around it (+11.5/-11.5). Do you see any variation in intensity when you operate the INTENS control? If so, then this section is probably OK, but it might be worth checking the biasing resistors in case any have drifted value - R620, R621, R622, R623, and whether R624 is open.

If BIAS INTENS is at 82v as indicated then your HV output is probably OK.

Have you checked voltages around VR604 as well as VR605, also the heater voltage (F1/F2)?

 

[mpavlica]

Yes, I do see, a very small, from complete loss of beam, up to just to see it when it is at MAX
VR604 and VR605 voltages are same as in manual. Heater voltage is 6,3 so thats fine.
Also, resistors 620 up to 624 are okay and within specs.

[mpavlica]

OK, I just took my TDS3014 to measure some signals, i used multimeter before...

So,  ZUP SQW from TB board is okay
First photo shows square wave signal at D613 ANODE. Looks okay
Second photo shows signal at cathode D613 / anode D612
Third photo is signal at cathode of D612.
Any ideas?