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Peavey PV-1.3K power up mute.
Peavey PV-1.3K power up mute.
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Old 10th January 2019, 08:18 PM   #1
Boelserwis is offline Boelserwis  Poland
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Location: Fajslawice, Poland
Question Peavey PV-1.3K power up mute.

Hello,
My name is Boguslaw, I am from Poland.

I'm new to this forum and have a question about repairing a old Peavey PV-1.3K power amp I am using.

Unfortunately, I do not speak English and I am using an interpreter, so I can translate something wrong. I am asking for understanding.

The amplifier works well, however, the power up mute system does not work.

2 seconds after turn "off" the power switch, appears thump might in the speaker on channel A, and another 5-6 seconds later thump might in the speaker on channel B.

I've tried everything, but I can not deal with this problem.

I will add that I also use the Peavey PV-4C amplifier, in which this problem does not absent.

I do not know if the fault is on the driver's board or on the output board? Or maybe the capacitors in the power supply are a problem?

I have a schematic, but the construction of the PV series is specific.

I am asking for help and hint which elements are responsible for muting the speakers after turning off the power supply?
Which elements should I check or replace?

Greetings from Poland!
Thanks.
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Old 11th January 2019, 12:54 AM   #2
indianajo is offline indianajo  United States
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q101 & Q201 silence the inputs of the respective channels. Likely the timeout capacitors C107 c207 are dried up. As are all other electrolytic caps at this age. these are on the input boards. check the +-16 power supplies while you are at it. Sometimes output failures cause the zeners to these to blow up, but cheap repairment don't check that far back. If the +-16 make a sudden shift, that could cause a whomp noise. Set meter up before you turn it on to monitor those supplies, that they ramp up smoothly and together.
Notice on these the harness allows you to reverse the position of the input boards so you can work on the one on the bottom. Just put bottom on top and flip the harness ends.
Looks like you lucked out in Poland this month. all the snow is in Austria and Italy! We're getting our snow tomorrow. Last week it was 25 deg C & sunny here!
best of luck.
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Last edited by indianajo; 11th January 2019 at 01:07 AM.
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Old 11th January 2019, 08:15 AM   #3
Boelserwis is offline Boelserwis  Poland
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Thank you indianajo for a hint.
I suspected these capacitors, I even bought them, but I did not replace them ...
The output board is functional and has never been repaired, but I will also check these zener diodes. I am taking repair.
For me, in the Lublin area we have snow and -9 degrees Celsius.
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Old 11th January 2019, 09:28 AM   #4
Boelserwis is offline Boelserwis  Poland
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Voltages measured on P102 pins have + 16,87V and -16,06V.
I do not know if this level of tension is acceptable?
I took care of channel A. If I manage to fix it, I will take care of the repair of channel B.
Unfortunately, replacing the capacitor C107 did not give anything.
I tried to replace the transistor Q101. I used BSJ174, which according to datasheet is the equivalent of J174, but it did not help.
I also replaced U100, U101, U102 substituting them with a functional PV-4C. With no effect.
I will try to replace C106, C119 and C112, but I have no hope ...
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Old 11th January 2019, 01:31 PM   #5
Boelserwis is offline Boelserwis  Poland
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error... measured voltage is +16.87V and -17.06V
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Old 11th January 2019, 05:38 PM   #6
indianajo is offline indianajo  United States
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Well, .3 v difference in power supplies is not significant. .9 v would be.
BTW my PV-1.3k doesn't whomp powering off.
I would check the J174 before replacing. They should measure a fixed resistance from both ends and a diode drop (.6v) from gate to each end. Of course infinity backwards.
J174 are getting very hard to get here in the US. I bought a few from ON semi at $.35 a few years ago, now farnell has some from a nobody factory for $2.50. There are also two pinouts of J174, the Nat Semi with gate in the middle and the Phillips with the gate on one end.
Next thing to do is measure with an AC analog voltmeter through the signal path and see where the turnoff whomp is coming from. Then examine the first stage where the whomp appears.
You may have a RMS digital AC voltmeter at school, but since they are minimum $170 here and don't measure above 7 khz, I don't have one. My regular DVM produce random numbers on music frequencies other than 50 and 60 hz. BTW dual slope integrator DVM average signals over a couple of seconds, are fairly useless for transient pulses.
I use an anolog voltmeter with 2 vac and 20 vac scales. The needle will kick on a 100 ms pulse. In a fully equiped lab a memory scope would help with the trigger set to a suitable DC value to only trigger on the whomp sound. Those were $7000 last time I shopped for a tek 377.
You might have a failed cap somewhere else throwing power supply voltages off. I wouldn't suspect anything in the output stage. How old are the e-caps on the +-16 v? This would be on the power supply board in the bottom.
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Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 11th January 2019 at 05:47 PM.
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Old 11th January 2019, 09:51 PM   #7
Boelserwis is offline Boelserwis  Poland
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Thank you indianajo.
In fact, capacitors in the +/- 16V power supply can be important.
I did not think about it. If the voltage supplying the preamplifier is lost sooner than the supply of the output stage, then the silencing system will not work ...
Tomorrow I will try to replace these capacitors.
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Old 12th January 2019, 03:10 AM   #8
indianajo is offline indianajo  United States
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Taking data with a fast meter may help find the stage that has the problem. Yes, the electrolytics in general need updating, the small ones more than the rail caps i have found. New 1500 uf caps will keep the +-16 zeners from being blown.
But PV-1.3k was a bargain amp. They didn't go cheap on the output transistors, but they did on the caps on the driver board. There are lots of little 1 and 2.2 uf ceramic caps rated at 50 v. They provide local stable +-16 voltage to the op amps and such. Those are cheap as dirt and one might be shifting leakage current as voltage collapses. I sure had a lot of them open up. Finding the stage where the power supply shifts, or the output shifts, is where to replace those. They may not be off value in capacitance but may leak under 16 v. I also had one of those green cylinder capacitors that look like resistors in the VI limiter circuit open up.
Zeners are also failure prone parts after more than 10 year life. That funny +16 voltage you got may have not been an error. It may have been a variation.
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