SX-1250 Problems After Rebuild

ILikePioneer

Riddle Me This!
Good Morning, I have just completed a 1250 rebuild with the help of parts list from MTF and Mattsd, thanks guys. Here is my problem: getting ready to power her up on the 100 watt DBT I have just the protection and stabilizer plugged into the unit. I get a dim bulb and 65VDC on both sides of the stabilizer. I then attach one of the power amps to the left side of the receiver, the bulb dims but not all the way and now i'm getting 40VDC on the stabilizer both test points. Same thing with the right side power amp board. Idle current is out of whack on both power amp boards. I rechecked all my transistor and cap positions on both amps and all look ok. I did have a slight problem with the equalizer when rebuilding that. Before I started redoing that board I noticed an entire trace was lifted and broken on the back of the board. I fashioned a jumper wire to connect the base of Q12 to R41 & R42, not sure if that is the problem but I'm stuck here now.
Schematic is attached of the equalizer.

Thanks for the help!
 

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Your going to have a nice pioneer collection, or is this the second 1250? :D

Recheck the output locations on the heatsinks. I used "mattsd" restoration Thread for guidance. He has before and after photos of all the board assemblies and heatsinks. Compare the photos to yours. The EQ board has a voltage regulator on it. Check the voltages on the EQ with just the Stabilizer plugged in. This is a safe start to trouble shooting the issues.

Also: You should post all the voltages on both the Stabilizer and EQ boards without the amps connected (on the DBT. What wattage bulb are you using?).
 
FWIW, a 100W bulb in the DBT may not be sufficient to get line up to the point where the regulators have enough bus voltage to work with. From my notes taken after reworking my 1250, the DBT ended up with a 150W lamp to get a reasonable start with reasonable operation, and even after that the voltages had to be readjusted after going to line voltage.
 
Thanks guys, the outputs are installed correctly, I am using a 100 watt DBT, I have used that a few times before for a 1250 resto....when powering up only with the protection board and the stabilizer, the relays both click and I get 65VDC on both test points, once I attach a power amp on either side the stabilizer drops to 35-40VDC....
 
Hello,
disconnect one of the Power Amp modules, maybe one of them is bad. If the speaker relay energizes you have the good one
 
what are your initial offset and idle current settings - never mind the cw and ccw bupkus, idle current pot should be zero ohms indicated on real test.
 
Hi Mark, the idle current pots are at 1.2ohms and the offsets were high and not near zero OHMS, I dialed them back down to 1.3 OHMS, could that have been the problem?
What is my next step, power up on DBT?
 
thanks echowars, i went and adjusted the offset pots, does anyone have an idea about whats going on with this...

thanks
 
Keep the amp boards disconnected and go full line on just the stabilizer and protection boards (You said you had a good dim bulb and could set the regulated supplies). Set the regulated 65v to +- 65.5v. This will get the set up to line voltage. Go back on the DBT and connect one amp board. set the bias to zero volts and see if the idles respond to VR movement. I used the MJ21193 and 94's so the best Idle I could get was 50mv but you are "Tickling the dragon" on the DBT so just check and see how the VR's are responding. One amp board at a time. Its been awhile but I think the 100 watt is good for the adjustments. Its been it my rig for over a year and I have completed at least one 1250 since then.
 
Keep the amp boards disconnected and go full line on just the stabilizer and protection boards (You said you had a good dim bulb and could set the regulated supplies). Set the regulated 65v to +- 65.5v. This will get the set up to line voltage. Go back on the DBT and connect one amp board. set the bias to zero volts and see if the idles respond to VR movement. I used the MJ21193 and 94's so the best Idle I could get was 50mv but you are "Tickling the dragon" on the DBT so just check and see how the VR's are responding. One amp board at a time. Its been awhile but I think the 100 watt is good for the adjustments. Its been it my rig for over a year and I have completed at least one 1250 since then.


took the words out of my mouth zeb... :D :thmbsp:

one amp at a time, checking to see if it behaves itself.

one addition:
at each stage (no amps, left anp only, right amp only) measure the awr-107 R3 and R4 voltage drops ACROSS each resistor, not ground based, one dmm lead on each side of that resistor at the same time.
That will give us the total current drains, and we will have a fighting chance of figuring things out.
OH, and before powering up, be absolutely sure the 10 ohm resistors ARE 10 ohms and not damaged.
 
As the regulator warms up (and it really, really does warm up), the +/-65V rises. If you set to +/-65.5V, after as hour or so you'll probably be over +/-66.5V. Set to 64.5V for now.
 
Thanks guys for helping out, here's what I did so far...

Powered up full power with just protection board and stabilizer attached, both power amps have been disconnected. Powered up fine, both the soft start and the protection relay clicked in nice. I adjusted the stabilizer on both test points to 64.5V as suggested by Glenn. I then took measurements of R3 &R4 on the AWR-107 power supply board.
R3- full power -0.448VDC
R4- full power +1.056VDC
Next should I go back to dim bulb and test one amp at a time? If so and I'm getting low stabilizer voltages what next?

Thanks
 
Ok left amp attached, 100w dim bulb test. Fired up no relay click(either one), bulb semi dims. Bias set to 0VDC..Getting 135mv on amp with trimmer fully CCW, turning the adjustment does nothing...No smoke , no smell...Readings from power supply resistors:
R3 -0.555VDC
R4 +0.351VDC
 
Right amp attached, left amp disconnected. 100w dim bulb test. Fired up no relay click(either one), bulb semi dims. Bias set to 0VDC..Getting 135mv on amp with trimmer fully CCW, turning the adjustment does nothing...No smoke , no smell...Readings from power supply resistors:
R3 -0.555VDC
R4 +0.351VDC
Same exact results as left amp. Where now?
 
Set the +- 65v on dbt (150w if possible) before repeating.

Please redo R4 and R3 with both amps disconnected.

1.056v unloaded to 0.351 with the addition of either amp has me puzzled, need quiescent drain anyway.

WHICH trimmer? The offset voltage adjust or the idle current set. It is ambiguous.

Be SURE when testing Idle current it is left at minimum / 0 ohms.

edit:

Bias set to 0VDC..Getting 135mv on amp with trimmer fully CCW

so 135mv is idle current and is unaffected by VR2?

take / post voltage readings of Q4, Q6 including a reading across r16 220 ohms.
 
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I would recheck Q7, 8, 9, and 10 for placement and orientation. It would be strange that both boards would have the same self induced problems. Anyway recheck all the trace connections on the boards and wait for more experienced help.
 
Yes idle is 135mv fully counterclockwise. Adjusting it makes no difference. I will recheck the resistors tonight. Zebulon I have checked leg placements many times already. They are all good
Mark readings of Q4 and Q6 on the power amp board?
 
yes, q4 and r16 are vital.

can you SEE the resistance on vr2 go from 0 to 500 in circuit when adjusting it with board out and no power?

have zeb and you swapped pictures or just went with verbal descriptions?

Since BOTH are acting the same, there has to be an error or miscommunication somewhere.
 
I know my questions are more related to my brain and can be annoying but both boards not working? Two separate systems, with the same problem? Sounds like a procedure error. Could you of used the wrong transistors by inadvertently swapping their positions? Note: Not just leg placement but actual transistor positions.

Sorry if I keep hitting you up on this. I know how it is. If on one set I didn't look a million times and didn't see my duff.
 
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