HK 930 main fuse keeps blowing
- Thread starter TheStump
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- help needed solid state
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Welcome to AK.
Do you have a dim Bulb Tester, if not then do an AK search and build one, you will need it.
I'll track down the service manual. You may have blown the rectifiers or...
Important, if you are not sure then ask, plenty of people on AK to help. Had one guy smoke a nice amp because
he couldn't wait an hour.
Do you have a dim Bulb Tester, if not then do an AK search and build one, you will need it.
I'll track down the service manual. You may have blown the rectifiers or...
Important, if you are not sure then ask, plenty of people on AK to help. Had one guy smoke a nice amp because
he couldn't wait an hour.
Are you saying you shorted the +B1 and +B2 pins on the predriver board, in which case the DBT may not be required.
Both +B1 and +B2 are at about +34V, you would be unlucky if you did any damage to components on the predriver board.
Visually check for any heat stressed/charred components in the power supply and predriver boards. Candidates being,
R610, 604, 605, 630, 624, 625. You should diode test TR605 and 625. Incircuit should be ok. All resistance checks and diode
tests with amp unplugged. Nice graphic from markthefixer on diode/transisor testing
Both +B1 and +B2 are at about +34V, you would be unlucky if you did any damage to components on the predriver board.
Visually check for any heat stressed/charred components in the power supply and predriver boards. Candidates being,
R610, 604, 605, 630, 624, 625. You should diode test TR605 and 625. Incircuit should be ok. All resistance checks and diode
tests with amp unplugged. Nice graphic from markthefixer on diode/transisor testing
Only got a few minutes.
Suggest you diode check above mentioned transistors and measure resistances with amp unplugged else sparks will fly.
Use the diode function on your multimeter. RED/BLACK in graphic refer to probe orientation. Expected results are 650mV
(550mV-800mV) or OL/Open circuit.
OK that it's bright at initial power on, but if it remains bright then you still have a short.
Do not undo wire wrap as a general rule. Looks like you've got a short somewhere so this action is unnecessary.
Suggest you diode check above mentioned transistors and measure resistances with amp unplugged else sparks will fly.
Use the diode function on your multimeter. RED/BLACK in graphic refer to probe orientation. Expected results are 650mV
(550mV-800mV) or OL/Open circuit.
Not sure if you have resolved your issue. If main fuse is the issue, check the bridge rectifiers. I had the same issue before and then I found one of the bridge diodes shorted out.
Also, how do you remove the predriver board for recapping? I found it pretty difficult with so many wires connecting the board at the bottom.
Also, how do you remove the predriver board for recapping? I found it pretty difficult with so many wires connecting the board at the bottom.
I fixed the bridge rectifiers, but have found that a problem still persists in the output phase. With the pre/main jumpers removed there is dc in the output. All of the 2sc897 are fine, so I will proceed to check the other semiconductors.
As for removing the prescriber board, I remove the output transistors from the heatsinks and take out the heatsinks. I keep all wires attached to the terminals since they are a huge PITA to put back on. With the heatsinks out and the predriver board no longer secured to the chassis, I carefully maneuver it so my iron can reach the contacts with adequate space and I do my work.
I will say that if all you want to do is recap. Don't do it. There is a very good chance nothing is wrong with the capacitors in place. Unless there is a leaky cap, I wouldn't do the work since the terminals are prone to get loose from the board and you could end up with the same problem I have right now or even worse.
As for removing the prescriber board, I remove the output transistors from the heatsinks and take out the heatsinks. I keep all wires attached to the terminals since they are a huge PITA to put back on. With the heatsinks out and the predriver board no longer secured to the chassis, I carefully maneuver it so my iron can reach the contacts with adequate space and I do my work.
I will say that if all you want to do is recap. Don't do it. There is a very good chance nothing is wrong with the capacitors in place. Unless there is a leaky cap, I wouldn't do the work since the terminals are prone to get loose from the board and you could end up with the same problem I have right now or even worse.
I finished a complete recap on an HK 930 yesterday. I have done dozens, up to and including Sansui G-9700, G9000, etc. This one was tough, but went brilliantly. Doing the Pre Driver board last, and it was difficult to pull the board out far enough to work on, but not that bad. Just loosen the wiring harnesses under chassis and board puls out nicely. Thought I was done, and did a successful DBT. It sounded perfect so I kept running it with the DBT for about 15 minutes when bulb flared and I lost sound. I quickly turned off HK. No fuses were blown, but now when I run a speaker load PA seems like a dead short. I hate these fused speaker protection units. I dissagree with previous post, I like to recap everything, they do sound better after, although I did advise this client not to rebuild this 930, as it sounded pretty fair, but because I knew it would be a difficult rebuild. Also no FM reception, is it likely to be the Motorola MC1307P IC? Gonna be at it again tomorrow.