CROWN 5000VZ |
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kedwardsleisure
Old Croc Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4938 |
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if the temp measurement is out of spec is must be fairly simple. It's a 3-legged IC (looks like a transistor) embedded in the heatsinks. The signal comes out of this and goes right up to the main control board with very few components in between, a couple of resistors etc, check the diagram.
I have had the tracks rot through underneath the actual ribbon cable headers. I remove them, fix the track and then fit new headers for reliability's sake. Once the temp is in spec you can look at the current feedback rails from the output modules, they're sampled across the emitter resistors. They're combined and added into the ODEP integrating circuit. Again the diagram shows where the signal path goes. There's a signal for each of the 4 parts of the output stage (low side npn/pnp and high side npn/pnp). You wont get any bias reading if the amp is in fault protect mode as the protect and/or odep circuit removes drive from each section. Everything else should be working first. I'm sure it must be something related to corrosion as you found so many tracks open. It could even be a resistor, as damp can leach up the legs and impair the lead-to-body connection. Check the static and dynamic balance pots as they can fail open to give strange fault symptoms. It might be worth seeing if you can get 1 side working first using the best of the 4 output boards. You can remove the AC fuse in the other channel and leave its output board out of the amp. Removing the fuse means the capacitors on that side wont be charged to full with no discharge path while you're working on it. The amp won't mind and is capable of working with just 1 side ok and the other either dead or missing. Once you've got 1 side working then you can use the 2 good boards to fault-find the opposite channel. I'm assuming you're happy with the power supplies and soft start etc on both sides and that isn't leading us up the wrong path. The feedback loop for the amp comes right off the back of the rear speaker terminals (literally) so the gold flexi foil ribbons must always be connected when doing power-on checks. |
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Kevin
North Staffordshire |
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richardleonard
Registered User Joined: 07 May 2020 Status: Offline Points: 12 |
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Thanks again for your helpful reply. Great idea regarding swapping between the boards, i will definitely try that next.
Regarding the temperature measurements... I have found U500 and U501 on the boards and schematics. U500 is connected to three resistors
On both boards I can confirm that the resistors above read within 5% correctly, and the traces connecting them to U500, as well as the traces from this temperature circuit to the +15V rail and TEMP rail are measuring with continuity. U501 is connected to three resistors
On both boards I can confirm that the resistors above read within 5% correctly, and the traces connecting them to U501, as well as the traces from this temperature circuit to the +15V rail and TEMP rail are measuring with continuity. This suggests to me that the temperature measuring circuit is working correctly. At this point should we assume that the temperature circuit is working correctly and it is measuring high voltage due to excess heat? |
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kedwardsleisure
Old Croc Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4938 |
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I dont know..are the heatsinks getting hot?
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Kevin
North Staffordshire |
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richardleonard
Registered User Joined: 07 May 2020 Status: Offline Points: 12 |
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I mean... given that the voltage is shown literally the moment it is turned on, i suppose it rules that out too. They certainly don't feel particularly hot.
I tried your board swapping suggestion... very interesting results. So I used the best looking boards, and avoided the one with the 3.5v out of spec temperature reading. I removed the 20a fuse from the unused side of the amp. Now - when powered on, instead of the fans spinning at full speed they barely move, just turning ever so slightly. The DC/LF lights are still on on both sides and the (even with missing output board on one side!) and the SIGNAL / IOC and Load / Limit lights are also still on on both sides. I note that the SIGNAL / IOC light is flickering now on the side with the amp board and fuse present. The temp readings are normal at 3.01 and 2.99 respectively. Odep still doesn't kick in.
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kedwardsleisure
Old Croc Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4938 |
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Ok, you're making progress.
Ignore the fault lights on the side with no fuse! If the fans are now just ticking over then that's a start. It means one of the boards you've taken out was making that happen. Ignore the signal/IOC lights for now, they will come on if the amp can't null the error amp, which it only achieves when the amp is actually working properly. If the load-limit light is on, it means the circuit thinks the module is taking a substantial current, so I would investigate the signal paths (tracks etc) between the current sense lines (the long thin lines that radiate from the emitter resistors) all the way back to the top board. The diagram will show you where they go. The schematic tag numbers start IC..something (there are several per bridge section). The lines are integrated, summed and consolidated in quite a complicated manner, hence why its important to try and ascertain exactly which board the fault is on! Very occasionally a fault on the output board(s) makes it up to the main board, though usually as a result of blown output transistors. The main boards come in lots of revisions if you need to trace the circuit, so make sure you have the right diagram for those. The output module boards dont really vary if at all. |
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Kevin
North Staffordshire |
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richardleonard
Registered User Joined: 07 May 2020 Status: Offline Points: 12 |
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Sorry for the delay.
I have done a great deal of investigating of the output boards. I can say with absolute confidence that EVERY trace is intact. The current sense lines included. I have further evidence for this claim. After doing all this work - I took the two boards which were not setting off the fans on channel 2 and moved them over to channel 1. The fans spin at full speed again! This suggests to me that the problem is on the main board, rather than the output boards... would you agree? I've also found that the heatsink temperature measurements have not followed the output boards. So putting these two 'good' boards in channel 1 - they now measure the same as the other boards did in channel 1 with one of the temperatures reading at 3.5v. According to the manual, the temperature sense drives an over-temperature amp U117A. Would that be a good place to check next? |
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kedwardsleisure
Old Croc Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4938 |
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the temp signals are buffered by U10 for the test points, and U117 for the odep circuit. I suppose it's possible that one or the other IC has failed in a way that tries to drag down (or pull up) the temp signals somehow. But I would still concentrate on getting one side working fully, otherwise putting what might be a faulty output module into a channel with other faults already might have you chasing round in circles.
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Kevin
North Staffordshire |
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richardleonard
Registered User Joined: 07 May 2020 Status: Offline Points: 12 |
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I don't think there is anything wrong with the output boards - i've pretty much checked every component on every output board at this stage. I think the problem must be with the main board or power supply. I'm totally tearing my hair out here :(.
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1103 |
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It sounds like a heat sensor problem to me, for the sake of just replacing both and the fact they are only about £1.00 each could save you a load of grief in labour time.
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richardleonard
Registered User Joined: 07 May 2020 Status: Offline Points: 12 |
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Are you referring to the ones in the heat sinks on the output boards? I think it’s unlikely to be them because the temperature readings stay the same when I swap boards between channels 1 and 2?
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