Hi Lyle,
My comments are below:
On Fri, May 6, 2022 at 02:18 PM, <lylejlarson@...> wrote:
Heres a summary of what Ive done:
Using isolated PS503 and (2)PS501 Supplies I measured:
Voltage across C1066: 0 Volts.
Also, Voltage across C1025: 0 Volts.
Voltage at Q1021-C: 1.5V
Voltage at Q1021-E: Around 20V or more.
Voltage at Q1021-B: 6.5V (!)
Voltage at Q1022-C: 6.5V => No current thru R1023
Voltage at Q1022-E: ~6.0V.
Voltage at Q1022-B: 6.5V
2465 schematic I found is missing proper measurement references, there is only one (REF) line. If you look at 2465B PSU schematic, which is almost identical, some voltages are measured wrt REF1 (inverter driver ground), and some measured wrt REF2 (U1030 ground). Voltages around Q1021 are measured wrt to REF2, makes more sense as U1030 supply is built on top of REF2.
From your comments I assume you already know how to deal with measuring signals with floating high voltage reference points using an isolation transformer and safety precautions.
¡.
All of the supply outputs are all behaving similarly. Most exceed their
listed voltage
levels when U1030 stops pulsing.
Some possibilities:
1) There may not be enough load. Is fuse F1102 intact? From your comments about +10V I assume the PSU is connected to the rest of the scope. You can also test PSU in isolation by connecting one 2-ohm 25W to P232 and one 2-ohm 25W to J303 (+5VD) as described in the service manual. Others had the PSU running with only one 2-ohm 25W if you only have one such resistor. Running the PSU with the dummy load is better especially if some voltages are overshooting.
2) Another (unlikely) possibility is over voltage protection, U1030 pin 15 is kicking in. Pin 15 of U1030 wrt REF2 (ground of U1030) should be ~ 0.8V according to the schematic. If it gets close to 0V that says primary voltage of T1060 exceed the limit and error amp will turn off the switcher.
If over voltage is the issue, and FB path is suspect, disconnecting the FB line should run the switcher at the lowest primary voltage.
However, I don¡¯t think this fault puts the switcher in ticking mode so it is unlikely.
3) Over current, perhaps some caps or diodes in the rectifier section are bad. R1050 is the sense resistor. if Q1040 turns on, it turns off the supply to U1030. PSU is disabled until C1023 charges again and C1025 charges back to trip voltage of Q1021 network. Once Q1021 turns off, its emitter needs to charge back to ~ 20V or so before it turns on again because of the hysteresis through R1024.
You can tell if overcurrent is the issue by measuring the voltage across C1023 and C1025 wrt REF2. If C1023 drops below ~ 7V at ticking rate while C1025 is still above ~13.2V then over current is triggered. You can also measure Vbe of Q1040 but it would be more difficult with all the switching waveform.
Over current circuit is interesting, it depends on CR1040 to be a Ge diode so that Q1040 is off until ~ 0.3-0.4V is dropped across R1050. Mentioning it just in case it was replaced with a Si diode.
Time constant of ticking with a short would be similar to what you are seeing.
The FB line has a very suspect shape. Dropping , I'm going to
Disconnecting FB runs the switcher at its lowest output voltage, if ticking is still going on without FB line FB signal is not the issue. Using a dummy load and testing PSU in isolation doesn¡¯t apply any FB signal and it is a good test too.
check LINE UP, and FB, then PWR UP
Line Up and Power Up just tell the scope power is good. I don¡¯t think an error in those lines could put PSU in tick mode.
Pulses seem clean at U1030.9, but weak and faulty (not clean pulse) throughout
the "Inverter Drive" Section.
This could also be the reason for over current. If only one driver is on, current is applied to one side of the transformer only and primary would look like a DC load. Q1060 and Q1070 should alternate at every pulse from U1030. Or if there is no drive to Q1060 and Q1070 there won't be any pulses in T1050 to keep switcher going. Since you are measuring some voltage at the secondary one of the driver transistors should be passing current though.
Ozan
On Fri, May 6, 2022 at 02:18 PM, <lylejlarson@...> wrote:
...
Connected to Line voltage. The ticking is back. With each tick, the 87V UNREG
line
spikes near 120 V, (but it varies considerably), 42V UNREG behaves similarly,
but with ~1/2 the voltage. Blower motor turns about 1/2 rotation with each
tick.
I can think of two possibilities (not to say these are the only two possibilities):
1) There may not be enough load. Is fuse F1102 intact? From your comments I assume the PSU is connected to the rest of the scope. You can also test it in isolation by connecting one 2-ohm 25W to P232 and one 2-ohm 25W to J303 (+5VD) as described in the service manual. Running the PSU with the dummy load is a better idea especially if some voltages are overshooting.
2) Another possibility is over voltage protection U1030 pin 15is kicking in. Pin 15 of U1030 should be ~ 0.8V according to the schematic. If it gets to close to 0V it will turn off the switcher. If over voltage is This could be related to FB signal, disconnecting the FB line should run the switcher at a lower primary voltage at T1060.
Pulses seem clean at U1030.9, but weak and faulty (not clean pulse) throughout
the "Inverter Drive" Section.
