• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Onkyo TX-2500 no power

bzb882

bzb882

AK Subscriber
Subscriber
I bought a 2nd TX-2500 for the faceplate glass and the bonnet. It looks so pristine I don't want to use it as a parts unit. As advertised it does not power up. All 4 fuses test good as does the power cord. I tried cleaning the power switch with deoxit and used a jumper wire between the two wires attached to the power switch. No go. I removed the jumper wire and verified that I have 120 VAC at the two wires connected to the power switch. However, when I engage the power switch that drops to either 0.022 VAC or 5.022 VAC. There's no relay, but I'm guessing some sort of protection circuit is doing that. Any ideas as to where to look?
 
Register to hide this ad
i just picked up a tx-2500 mkii, I am no expert but it appears that there is a protection circuit. Page 6.
 
The protection circuit won't drop power to to the power switch. That should be a constant.
The protection circuit will not work if the power supply can't produce the voltage needed for that circuit to even work.

Seems you have a power supply problem.
 
Many transformers have an internal primary "safety" fuse. Supposed to open up if transformer overheats, but sometimes (with age..) just goes open. Power off, measure the resistance of the primary winding. If open, may be the culprit. Some times the transformer can be opened and the fuse link replaced. Sometimes just need a new transformer. (but sometimes it's something else....) No documentation in the manual.
With unit unplugged, measure resistance between yellow and whit primary leads of transformer. Should be a couple of ohms DC. good luck,.
 
sregor said:
Many transformers have an internal primary "safety" fuse. Supposed to open up if transformer overheats, but sometimes (with age..) just goes open. Power off, measure the resistance of the primary winding. If open, may be the culprit. Some times the transformer can be opened and the fuse link replaced. Sometimes just need a new transformer. (but sometimes it's something else....) No documentation in the manual.
With unit unplugged, measure resistance between yellow and whit primary leads of transformer. Should be a couple of ohms DC. good luck,.
Click to expand...

2 ohms, so transformer should be ok?
 
bzb882 said:
Thanks, sregor! Anyone have an idea as to what I should check next?
Click to expand...
Before powering up, check connections - one side of AC should go to fuse then to yellow lead, other side of AC goes to switch, then to white lead.
If connections are okay, plug in and turn on.
Next check secondary voltages. Should be about 6.3 volts AC between the two grey transformer leads, and about 50 Volts AC between two red transformer leads.
If AC voltages okay, check DC voltages on filter caps.
 
bzb882 said:
I bought a 2nd TX-2500 for the faceplate glass and the bonnet. It looks so pristine I don't want to use it as a parts unit. As advertised it does not power up. All 4 fuses test good as does the power cord. I tried cleaning the power switch with deoxit and used a jumper wire between the two wires attached to the power switch. No go. I removed the jumper wire and verified that I have 120 VAC at the two wires connected to the power switch. However, when I engage the power switch that drops to either 0.022 VAC or 5.022 VAC. There's no relay, but I'm guessing some sort of protection circuit is doing that. Any ideas as to where to look?
Click to expand...
How are you measuring the AC? When you measured across the open (off) switch you should have 120vac with the probes connected to each wire.
When you turn it on the switch completes the circuit and your probes are no longer inserted completing the circuit. Now you're effectively measuring with both probes connected at the same point.
 
Last edited:
Wiring looks correct to me. Here's the measurements I took:
Grey wires: 6.3 VAC
Red wires: 50 VAC
Back filter cap: 0.5 mV DC (positive terminal to ground)
Front filter cap: 272 mV DC (positive terminal to ground)
 
Looks like a short some where. I've had to study the schematic and see where I can remove parts of the circuit to find the short.

Not easy and can take time.

Have you studied the schematic? Can you read and understand it?

I'm traveling now so I haven't looked at the schematic but I'll try tonight.
 
Can you see any DC voltage after the 50vac rectifier? My guess this feeds the outputs.
 
<edit> updated voltages for tx-2500 schemo </edit>

Looks like b+ and b- is +-31v. I might pull the outputs and see if that helps.

Do you have the +-13v?

I also see +14v and +19v.

Do you have these?

If only the b+ and b- are missing maybe the outputs are the problem.

Seems odd both the positive and negative sides are out.
 
Last edited:
rickl said:
Looks like a short some where. I've had to study the schematic and see where I can remove parts of the circuit to find the short.

Not easy and can take time.

Have you studied the schematic? Can you read and understand it?

I'm traveling now so I haven't looked at the schematic but I'll try tonight.
Click to expand...
Really can't read schematics well emough to make a difference, wat should the filter caps have read (ballpark)?
 
I'd you decide to pull the outputs, I'd unsolder the pins and slip some heat shrink over them to separate them from the board. No sense making more work.
 
Don't know if this helps, but when I first powered it up (on my DBT) the light lit and then went out in maybe 2 seconds,
 
TX-2500 here:
Filter caps should be around ±31vdc. Points 15 and 16.

Screenshot (1422).png


Screenshot (1424).png
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom