Bottlehead Forum
Bottlehead Finished Products => Legacy Products => Topic started by: pdxgrampa on November 04, 2017, 10:10:56 AM
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This is not a new build has been in service off and on for a few years.
It would drop out briefly and then recover and then failed completely.
A side LEDs were on B side not then A side LEDS were off but MJE 350 was conducting.
H1: 24.5 VOLTS
H2: 29.4 VOLTS
A SIDE HIGH VOLTAGE B SIDE HIGH VOLTAGE
7: 223 VOLTS 7: 222 VOLTS
9 : 213 VOLTS 9 : 221 VOLTS
10; 204 VOLTS 10: 221 VOLTS
TERMINAL
12: 116 VOLTS
15: 78 VOLTS
21: 115 VOLTS
22: 21 VOLTS
31: 78 VOLTS
32: 115 VOLTS
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Are you able to post photos of the PC boards?
For the most part, on just about every Extended Foreplay III that I have serviced that was initially in working order, I end up building a new center PC board for the high voltage shunt regulator.
It's very easy to see if this is the issue, as the center board you have now will be a bit black under where the MJE-350s each sit.
-PB
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This the B side MJE 350
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Can you tell me what voltages you get at:
1. The metal tab of each MJE-350 on the center board.
2. Kreg A and Kreg B on the center board.
3. The metal tab of each MJE-350 on the outer boards.
4. The metal tab of each MJE-340 on the outer boards.
-PB
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Paul here is what you asked for:
All voltages referenced to terminal 18
The voltages on the side MJE 350s and 340s are all 78 volts
Tab on A side shunt reg board 350 is 117 volts dropping slowly from 123 at first measurement.
Tab on B side is 116 down from 126
A side Kreg is 0 volts
B side Kreg 7.5 volts
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Doesn't look like picture made it .
I'll try again
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Pull the outer two 12AU7s and retest the center PC board.
(Also, the MJE340 tabs should be a volt or two higher than the MJE350 tabs on the outer PC boards when all the tubes are plugged in and running)
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Ok tubes out:
A side B Side Shunt Reg
350: 146.8 volts 350: 146.8 A side 350: 149
340: 150.9 340: 150.0 B side 350: 148.5
A side Kreg; 0
B side Kreg: 8.72
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A side Kreg; 0
B side Kreg: 8.72
It's odd that the A side Kreg is stuck at 0V but the regulator appears to work. With 0V available for the TL431 to operate, I would expect your regulated voltage to be just a volt or two less than your unregulated voltage.
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PB,
Unless there is something else to measure/try
Should I just contact the Queen on Monday for a board and Parts?
Thanks for your help
Greg
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That particular PC board is NLA, and several of the parts are also no longer stocked in our inventory. There are some workarounds for this situation; feel free to contact me and we can go over the options to get you back up and running.
-PB
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Thanks Paul,
I didn't see a way to PM you.
so I will call the store on Monday if that works for you.
Greg
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You can e-mail me at pb(at)bottlehead(dot)com.
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Will do Paul
Greg