d500 signal loss

vmaxman

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#1
I hooked up a source to amp and get no sound from either channel, left channel meter does jump around, I assume signal makes it to that point. Can someone help me troubleshoot and locate source of signal loss. Amp powers up and speaker relay engages, happy thanksgiving to all
 

grapplesaw

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#2
Good you got the resistors fixed John

We are traveling so hope you get some ideas here.
I still think you should remove control wires and bypass the speaker out put and power relays till you get it putting out on both channels. Use the variac to power it up and discharge the main caps when working on it when switched off. Remember that think had 240 volts that can kill you.
Did you do full test off both channels through dim ups first?
Did you measure dc offset after dim bulb is removed.?
Did you measure bias’s for both channels?
Do you have signal voltage at the input On the control board connections ?
Do you have signal voltage between the blue and violet wires connected to the bases of the m21195’s?


John you have follow from the start point and work your way through.

Let’s hear on these item Ok
 
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vmaxman

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#3
To be clear I am to d/c all wires from the front relay, Leave the middle relay as is. bypass the rear relay? This supplys power to the power amp board only? Power up with variac and DBT in circuit? With these in circuit where do I test DC offset? Bias measurement? What should the signal voltage be?
 

grapplesaw

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#4
Front relay is high low rail voltage center is on off back one is speaker output. Pull control wires from all three move wires on middleone and rear one so current passes through them. You no longer have on off button working. Use power bar to switch on and off

Did you power up through DBT with rail fuses in. You can test one channel at a time.
Bringing power up through variac allows you to watch DBT and react if it get to bright.

After testing supply current through DBT remove it from circuit is all is good

As to other tests John they are well laid out in the service manual as to how and where to test


Good luck and get some answers.
 

vmaxman

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#5
trying to be clear on bypassing relays. I am to bypass the rear relay (speaker relay) and middle relay. Front relay I should remove all wires from that relay. Correct? I will take a pic and send.
 

vmaxman

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#6
As far as speaker relay engaging, I was only using the variac in circuit, slowing bringing it up.
 

grapplesaw

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#7
trying to be clear on bypassing relays. I am to bypass the rear relay (speaker relay) and middle relay. Front relay I should remove all wires from that relay. Correct? I will take a pic and send.
Remove only low voltage control wires that come from meter board

in addition Move two wires on middle and rear relays. I emailed you all theinso on doing this while back. Do not remove or move the heavy red wires on the ffront relay
 

vmaxman

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#9
All of the 8 agx fuses are blown. DBT is plugged into a variac. I replaced them and without fuses in circuit DBT is Dim. With fuses bulb is bright and I have around 7dvc going to speaker terminals. Can I test the amplifier without output transistors in the circuit? Thanks
 

grapplesaw

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#10
John at this point I think you should think about shipping it to me. I will fix it for you in January if you like.
 

grapplesaw

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#11
When I repaired the boards they were tested on an other amp and had excellent specs.
Something is wrong in the main amp wiring. Period. I am sorry to say but you do not have the proper tools to repair this amp.

The unit is worth about $1,000 - $1,400 as is less eBay fees if you want out. Get it fixed it’s worth up to $2,500 with the repairs you have done
 

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mlucitt

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#13
I repaired a Hafler DH-500. They are not much different than any other half kilowatt amp. Standard troubleshooting rules apply to the PL Dual 500, extra caution is warranted around the power supply because it can kill you .0000001% easier than a PL 700.

Schematics are available I believe, and we have access to a great audio engineer who can help. Half the work is already done because the control boards have been tested sat by Grapplesaw.
 
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