This amp may actually be a Series VII in a VIII chassis not sure. Says ZEUS -1 on the board, and revision AA. Board is missing ALL TIP102 drivers in the PS/Vari circuitry. This board has no added components nor modifications what-so-ever.
Amp will work but from what I can tell the PS pulses on/off every ~1/4 second. I cannot probe pin #3 of the TL494 very well; especially unwell with a source plugged into RCAs. That source has common ground and good connections case-to-shields.
TL494
1. 3.384
2. 3.356
3. 4.61 <-- Had to measuring with Fluke 16 set to max/peak hold as it fluctuates every 1/4 second
4. 0.308
5. 1.479
6. 3.548
7. 0 <-- Black probe connected directly here
8. 14.19
9. 0.2 (Strobes)
10. 0.2 (Strobes)
11. 14.19
12. 13.62
13. 5
14. 5
15. 10.89
16. 6.75
Now, if I plug in something into the RCAs with good common ground the amp stabilizes slightly. As I increase input signal the amp becomes more stable.
Fear the PS FETs getting hammered on/off like this would cause failures.
Resistance between B- and RCA shields is 670ohm. Secondary ground is connected to RCA shields.
If I lower input voltage to about 10vDC, the amp locks into full duty cycle and stabilizes.
Any thoughts why this amp is cycling every 1/4 second at 14.4vDC?
Amp will work but from what I can tell the PS pulses on/off every ~1/4 second. I cannot probe pin #3 of the TL494 very well; especially unwell with a source plugged into RCAs. That source has common ground and good connections case-to-shields.
TL494
1. 3.384
2. 3.356
3. 4.61 <-- Had to measuring with Fluke 16 set to max/peak hold as it fluctuates every 1/4 second
4. 0.308
5. 1.479
6. 3.548
7. 0 <-- Black probe connected directly here
8. 14.19
9. 0.2 (Strobes)
10. 0.2 (Strobes)
11. 14.19
12. 13.62
13. 5
14. 5
15. 10.89
16. 6.75
Now, if I plug in something into the RCAs with good common ground the amp stabilizes slightly. As I increase input signal the amp becomes more stable.
Fear the PS FETs getting hammered on/off like this would cause failures.
Resistance between B- and RCA shields is 670ohm. Secondary ground is connected to RCA shields.
If I lower input voltage to about 10vDC, the amp locks into full duty cycle and stabilizes.
Any thoughts why this amp is cycling every 1/4 second at 14.4vDC?
A Audiopipe 2k i had here was doing the same thing , and it was Couple of output fets ( power light was flashing and there was a whine when cycling). i dont know if its a similar issue but i posted it.
Have all of the missing parts been replaced?
Does the amp produce audio at lower voltage?
Does it produce continuous audio when the supply is pulsing?
Have you tried to adjust the bias?
Does the amp produce audio at lower voltage?
Does it produce continuous audio when the supply is pulsing?
Have you tried to adjust the bias?
So, these boards I've seen often go through remediation where the PS is enhanced with added drivers and then TIP102 drivers are added to the Variable drive circuitry. This amp has none of those components provisioned nor retrofitted.
The amp produces audio at all signal AND input voltages. If it weren't for the pulsing I'd consider this amplifier to be -OK-.
I'm going to try posting a 1-minute video I think best describes the situation going on with the PS.
The amp produces audio at all signal AND input voltages. If it weren't for the pulsing I'd consider this amplifier to be -OK-.
I'm going to try posting a 1-minute video I think best describes the situation going on with the PS.
I set bias accordingly. No difference with setting bias. The amp also have a 56v pot. I set the positive rail to 56v. Neither fixed the PS pulsing.
In this video, 5uS, 2v/Div measured at a leg of one of the FETs. I varied input voltage from 9.9 up to 14.4, and then back down to 9.9. Adjusted input signal which is a 1khz sine wave. Amp is loaded with a 4-ohm load speaker. Obviously low amperage draw. Idles at about 1A. Peak about 2.5A.
I'm concerned about the PS pulsing at low signal input over 10vDC supply.
In this video, 5uS, 2v/Div measured at a leg of one of the FETs. I varied input voltage from 9.9 up to 14.4, and then back down to 9.9. Adjusted input signal which is a 1khz sine wave. Amp is loaded with a 4-ohm load speaker. Obviously low amperage draw. Idles at about 1A. Peak about 2.5A.
I'm concerned about the PS pulsing at low signal input over 10vDC supply.
I don't do video. They are virtually always useless for me.
Is the amp trying to overshoot the 56v rail voltage and that's what's causing the pulsing?
Is the amp trying to overshoot the 56v rail voltage and that's what's causing the pulsing?
56v rail is soundly set. Its funny you ask that though; because I have another Zeus VIII that is actually over-shooting. Similarly, there seems to be something a bit off regulation-wise in this amp and that one as well.
That's why I asked about the bias. The biased outputs might give enough of a load to prevent the overshooting.
Where are you getting all of these old hifonics amps?
That series 5 make me wonder how there could have any previous series.
Where are you getting all of these old hifonics amps?
That series 5 make me wonder how there could have any previous series.