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Amplifier Problems With a Sansui QRX-9001

K

Kaleb Martin

Active Member
Hello, I have a problem with the amps in my Sansui QRX-9001. The problem being they’re totally dead. Aside from the amps the entire rest of the receiver works great. I added pre outs from the preamp outputs, and have been using it with external amplifiers, and think it’s about time I got her working again. So if anyone has any ideas of what could be wrong, I would greatly appreciate your thoughts.
 
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I had that thought as well. So I had cleaned all the pots and switches, and checked the pins for the amplifier cards, and the surrounding pins in that circuit, and carefully cleaned the pins that needed it. But even so there was no change (besides not having any static in the controls).
 
Is it coming out of protect? There is no indicator on the QRX-8001 and 9001, you have to listen for the relay click a few seconds after power up. If no click, it is probably stuck in protect mode. The driver boards on these are plagued by low value fusible resistors (among other shortcomings of age related component failure). Could also have a blown channel, shorted outputs etc.

One other thought, the headphone jacks disable speaker output when headphones are plugged in. Could conceivably be a failure of that relay.
 
I forgot to mention that, yes it does come out of protect. But it seems to me that it comes out of protect too quickly. It takes it about 2-3 seconds to come out of protect.
 
I also checked the output transistors and many of the resistors in the amplifier boards. The outputs tested good, and all the resistors I tested were either within spec or quite close
 
If the unit hasn't been off for an extended time, 2-3 seconds isn't that unusual. Plug in some headphones and see if you hear a relay making (and breaking when you unplug the headphones). Only need to plug into to one of the two (front or rear) to trigger the speaker cutout relay.

No click there would indicate it is failed in the headphones mode. Maybe a long shot, but needs checking to rule out, if nothing else. Also check to see if you have audio through the headphones on both channels when plugged in.
 
I just checked, the relay does deactivate when I plug a headset in, and reactivate when I unplug the headset. And I do get sound out through the headset.
 
It’s puzzling, the entire thing works great even the protect relay, with the headset. I just have dead amplifiers. Do you think it could be a dead component on the protect board?
 
I can get activity from the front two meters, but only with the Dolby NR play cal, or record tone. I don’t even get meter activity on startup or shutdown.
 
Has the carrier board for the two pluggable decoder/synth boards been reworked to stabilize the vias (pass through solder joints)? Your last post in particular reminds me of the problems I had with the first 9001 I worked on ~20 years ago when the knowledge on repairing these was quite limited, compared to now.
 
This 9001 has been through quite a bit. I had bought it on eBay about 7 years ago. It had been supposedly fully restored and recapped. Low and behold, it was not. It was in terrible shape, so I took it to a tech in Texas, Dallas Vintage Audio. I told them to fix my problem, (nasty static, and failed solder joints on the 4-ch switch board). They fixed the static and recapped the amplifier boards, pre power supply boards, and the main power supply board. But the 4-ch board was still in dire need of re pinning, so I took it back and they covered that repair under warranty. About 2 years later I started to have problems with the 4-ch switch board again, so I took a look at it. It had not been re pinned, so I assume they just reflowed the solder. It was shortly after that, that I got a nasty pop sound, and there the amps went. So I decided to repin it, and fully recap the receiver. After that the amps still didn’t work, so I tried it using the record out jacks. That worked, so I decided to add pre outs to the preamp, and that worked, and it worked so well the sound quality blew me away, (I’m currently using two McIntosh MC2205 amps in place of the internal amps).
 
Just a side note, about a week ago my back right channel started to have an excess of static. I troubleshot the issue and found it was coming from the back tone card. Specifically the BA312 I.C. had gone bad for that channel, so I ordered the part and am waiting for it to come in. Since I had to tear back into her I decided I might as well go ahead and get the amps working again.
 
Aside from that BA312 I.C. and the amps, the thing works perfectly. The volume and filter board, the 4-ch board with all quad modes/circuits (including CD-4 which didn’t work properly until I recapped it), the Dolby NR circuit, and the tuner.
 
Ok. Wanted to make sure the 4ch switch board was out of contention as a source of problems. Probably need to verify operation of the protect circuit (including that the relay is passing signal even if it appears to be making when the coil is powered).

If you have good audio from all channels on the headphones, then the driver and main output stage are not suspect. At the risk of asking a stupidly obvious question, did the mod to add preouts leave the connections intact to the driver board inputs, or were main ins also added, using outboard jumpers going from the preouts to the main ins?
 
The connection to the amplifiers are intact. As the pre outs are only temporary, I just have wires connected to the clip harness making contact with the pins. It’s not great, but does the job. And another side note, I’ve learned that if the amplifier inputs are disconnected from the preamp, the protect relay stays in protect.
 
Careful of working around live voltages, do not attempt any of this if not sure of safety precautions!
Those amplifier boards are not happy when you dis-connect the harness due to the grounding design used. Do you have a way to limit current (dim bulb tester or variac) and a multimeter?
I am curious as to what values you see when measuring offset at the speaker terminals (if any)
You will want to have your meter hooked up to the speaker terminal red/black set to dc, volume at 0 (no volume) and observe behavior with speaker selector on when you turn on the receiver, see if the meter reacts. If it does not we will have to look at the feeds to the relay board pins 1 through 4.
With a scope it would be simple to trace the signals, without we will have to do some sleuthing.
Also need to verify voltages in a couple of places once you report back with offset readings, if not sure how to do that will walk you through the process.
 
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I have a multimeter, a variac, and a dim bulb tester. I do not have a scope. I just measured the dc offset. The offset is negligible. At power up it goes up to about 0.006 for an instant, when the relay kicks out of protect it goes to about -0.004 for an instant, and switching the speaker selector gives a drift of -0.001 to -0.008, and it always quickly settles back down to -0.001 or 0.
 
Need to carefully measure on the protection board dc voltage pins 1 through 4 to ground with receiver powered on. The zero voltage at the speaker terminals indicates to me that there is nothing getting through the relay.
 
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