QM-800 Help
- Thread starter QSilver
- Start date
QSilver
Super Member
I put in a new pair of driver transistors KSA1220AYS and KSC2690AYSTU and I still had the distortion... I thought the next thing to try would be to check the outputs. I pulled Q13 after fighting with the gunk holding the bolts on... It seems that the collector is connected through a threaded plate underneath that the bolts screw through and then the bolt onto the transistor makes the conneciton. I thought maybe a dirty contact might be causing the issue so I replaced the bolts, nuts and washers, and cleaned the TO-3 wings off with some wirewool.
I then refitted everything and powered up. The distortion didn't appear for a few second but after that, when I tapped Q13 with a wooden dowel, it would disapear and didn't come back for a minute or so - mean while I was tapping on the heatsink to try and get it to come back and it didn't. It still comes back occasionally but a light tap on the same transistor cures it almost instantly.
Should I keep on clenaing? I'm thinking of pulling Q13 from the other board and trying it in here just to make sure.... or I could just replace all the bolts and keep on cleaning the wings on the outputs off... I'm not sure which is a better idea....
I then refitted everything and powered up. The distortion didn't appear for a few second but after that, when I tapped Q13 with a wooden dowel, it would disapear and didn't come back for a minute or so - mean while I was tapping on the heatsink to try and get it to come back and it didn't. It still comes back occasionally but a light tap on the same transistor cures it almost instantly.
Should I keep on clenaing? I'm thinking of pulling Q13 from the other board and trying it in here just to make sure.... or I could just replace all the bolts and keep on cleaning the wings on the outputs off... I'm not sure which is a better idea....
QSilver
Super Member
I swapped out Q13 from a good and working channel, removed all the output transistors and cleaned the areas where the bolts contact the collector, then I reassembled it with new bolts all round and still had distortion.
I then replaced R8, R9, R10, R11, R34 and R36 and I STILL have distortion... but the smallest tap towards to centre of the board usually clears it up. Only thing I have found now is that when I have distortion, the collector voltage on Q13 drops down... would it be worth making a jumper wire to run from Q13 colector to R38 where the trace would usually carry it? I'm at a loss as to what to do next...
I then replaced R8, R9, R10, R11, R34 and R36 and I STILL have distortion... but the smallest tap towards to centre of the board usually clears it up. Only thing I have found now is that when I have distortion, the collector voltage on Q13 drops down... would it be worth making a jumper wire to run from Q13 colector to R38 where the trace would usually carry it? I'm at a loss as to what to do next...
QSilver
Super Member
Could this be a grounding issue? I tried measuring a voltage on the chassis and ground pin 13 with my black probe connected to my domestic grounding rod and I get a reading that sways from +100mV to -100mV if I attach a ground to the amp chassis from my grounding rod, I can hear a slight clicking through the speaker and soemtimes the distortion clears up. once it is grounded the chassis measures 0.1mV or 0. How could I isolate this? Any ideas?
QSilver
Super Member
One of those moments..... I think I might have tracked it down to the protection relay.... 
I'll try looking into that and see if it all goes away...
EDIT:
took the cover off the relay and worked the contacts while it was on and the slightest adjustment makes the distortion change or cure so I guess I need a new relay.
Any recommendations? The current one is an OMRON MY4.
The current relay is mounted with a bolt and nut between the coil terminals. Can I get a relay that will mount in the same way?
I'll try looking into that and see if it all goes away...
EDIT:
took the cover off the relay and worked the contacts while it was on and the slightest adjustment makes the distortion change or cure so I guess I need a new relay.
Any recommendations? The current one is an OMRON MY4.
The current relay is mounted with a bolt and nut between the coil terminals. Can I get a relay that will mount in the same way?
Last edited:
QSilver
Super Member
I fitted the new relay today - using the metal tabs either side of the mounting hole to hold the new relay in place as the new one doesn't have a threaded bolt or bolt hole. I next moved onto the speaker terminals for front left and right as these have been changed around.
Firstly, all the solder joints are poor or broken but there are two wires excluding the grounding wire to each speaker + terminal. The extra wires run from the protection relay to pin 8 & 5 on the protection board. The original rear speaker connector only has the wires from the relay and then ground connected to it and I can't find a mention of these extra wires running to protection post relay on the schematics... do they need to be moved or changed?
Firstly, all the solder joints are poor or broken but there are two wires excluding the grounding wire to each speaker + terminal. The extra wires run from the protection relay to pin 8 & 5 on the protection board. The original rear speaker connector only has the wires from the relay and then ground connected to it and I can't find a mention of these extra wires running to protection post relay on the schematics... do they need to be moved or changed?