Orion HCCA 225 Digital Ref will not power on - diyAudio
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Old 28th October 2011, 03:22 AM   #1
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Default Orion HCCA 225 Digital Ref will not power on

I bench tested a used HCCA 225 and it does not blow the fuse, but it also does not power on. It appears that the power supply is not coming up.There are no burn marks or discolorations anywhere. I checked voltage on the 3300 uF 50v caps and they are showing 13.3 V on both of them which is my supply voltage. I wanted to check some of the components so I pulled the board tonight (Thanks to Perry B. for showing me the trick for getting the clamping rails safely off) and everything I check appears good. I notice that there are large blobs of solder around one of the 3300 uF 50V caps legs so I have to think someone has been in here before. All of the caps I check are charging up and seem good with the meter.

Luckily I have a working HCCA 225 Dig Ref to compare my readings against. Unfortunately I do not have a scope to check any signals. I'm kind of surprised I was expecting to see LM317/337's in here for the low voltage supplies. I'm guessing that the extra 2N6488/2N6491 on each side are the low voltage regulators.

Anyone got any ideas on what I should check at this point?
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Old 28th October 2011, 11:34 AM   #2
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The digital reference amps had 2 different boards if I'm not mistaken. Post a photo of the board in your amp.
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Old 28th October 2011, 01:32 PM   #3
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Quote:
Originally Posted by Perry Babin View Post
The digital reference amps had 2 different boards if I'm not mistaken. Post a photo of the board in your amp.
Okay I'll get a picture of it posted this evening.

I stumbled across a partial 225 schematic, I think it might have been yours Perry. I'll try powering up the amp tonight and watch pin 12 on the TL494 to see if I'm getting the "on" signal. Are the TL494's prone to failure on these amps?
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Old 28th October 2011, 11:04 PM   #4
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Quote:
Originally Posted by Perry Babin View Post
The digital reference amps had 2 different boards if I'm not mistaken. Post a photo of the board in your amp.

Here are a few pictures of my amp pcb, hopefully these are good enough to identify it.

I am going to solder in some new power/gnd wires tonight and then I will run a few checks on it.

HCCA25_PCB.jpg

HCCA25_PCB1.JPG

HCCA25PCB2.JPG
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Old 29th October 2011, 01:11 AM   #5
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I finished installing my new power leads and checked pin 12 on the TL474, it does switch to 12.5 V when the remote signal is applied. I performed the diode test on the 4 MPSA's in the power supply section and they appear to be good.
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Old 29th October 2011, 05:22 AM   #6
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With the black probe on the amp ground, what is the DC voltage on pins 9 and 10?

With the black probe on the RCA shield, what is the DC voltage (positive and negative) on the various large emitter resistors?

Only list the greatest positive and negative voltages you find.
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Old 29th October 2011, 02:12 PM   #7
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Pin 9 - 4.89V
Pin 10 - 4.9V both in relation to amp ground.

The emitter resistors have all have +/- 22.1V on them in relation to shield ground. So the power supply is coming ON, but the ON LED is not coming on and there is no sound.

I checked the DC current draw on the amp and its idling at .77A. The DC offset at the speaker outputs is .02V and .03V.
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Old 29th October 2011, 06:32 PM   #8
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Its fixed.....I've got it playing on the bench now.

Thankfully it ended up being two simple problems. The first was that the gain pot has a dead spot in it that encompasses about 2/3 of its rotation. When I tried bench testing this amp the first time I set it for the middle of its rotation which also happens to be part of the dead zone. The second problem was that the Power LED wasn't lighting up. Someone had pushed on that LED in the past and it had a broken leg on it.

The combination of the two problems, no "ON" LED and no output had me thinking the amp was not turning on. When I realized that I had power showing everywhere throughout the circuit I started turning the gain pot up and when the pot finally made contact the volume was so high it just about blew my speaker. Scared the hell outta me too.

Does anyone have any recommendations for a good drop in gain potentiometer for this amp that they have used in the past?
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Old 4th September 2014, 05:46 PM   #9
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Anyone have a Orion HCCA 225 schematic, my intentions are to use the amp as a DC power supply to run a DBX processor.
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Old 5th September 2014, 02:34 AM   #10
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Please don't post in a repair thread that was started by someone else unless you are trying to help them.

Click on the red triangle in the lower left corner of your post and ask a moderator to move your post (and any replies to it) to a new thread (my post should be deleted).

After it's moved, I'll try to help you.
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