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Pioneer 1980 failing DBT

Leokarma

Leokarma

Well-Known Member
I recently got a dead Pioneer 1980 from an estate sale. Had the main 15A fuse burnt. Replaced the fuse, connected the receiver via DBT but it's failing the basic DB test. I used 60 watt, 150 watt and 200 watt bulb with same result. The bulb doesn't dim. Can someone help.....
 
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Unplug the amp boards completely and try the DBT again with a 100 watt bulb.
If it stays bright, rebuild the Power Supply.
If the amps are shorted out there will be some tears and alot of work.
This is the course troubleshooting method but you will get an idea of whats wrong with it.

Check this thread out!
 
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zebulon1 said:
Unplug the amp boards completely and try the DBT again with a 100 watt bulb.
If it stays bright, rebuild the Power Supply.
If the amps are shorted out there will be some tears and alot of work.
This is the course troubleshooting method but you will get an idea of whats wrong with it.

Check this thread out!
Click to expand...

Thanks and sorry for late reply as I was away. I just disconnected both the amp board, plugged it back and same result. It's failing DB test. I'm planing to completely recap this but before I do that I would at least like to troubleshoot and turn it ON. Is that possible ? Once I figure out what the problem is I can rebuild the PSW. OR do you still suggested that I rebuild the PSB first and then recap ?

One more thing. The original fuse that I have removed is white but the fuse I've replaced is the standard glass fuse. I hope this is ok right ?
 
It's failing DB test. I'm planing to completely recap this but before I do that I would at least like to troubleshoot and turn it ON. Is that possible ?
Click to expand...
method of elimination perhaps!
You have no idea where the short is, so you need to figure out where it is. You can start by doing lots of ohmmeter measurements, with power off of course, to help deterime the area in ?
OR
you can continue isolating loads on the supply to determine, if/where there is a short in the loads or if it is the p/s itself causing the short with no load. Isolating loads is a PITA considering that many of the loads are hardwired. The unit was never designed for easy troubleshooting.
As for the mains fuse, as long as it fits, is a fast blow type, the correct amperage and 250V you are good to do.
 
petehall347 said:
the manual shows various internal fuses ..try pulling them all out and see if bulb dims ..
Click to expand...

apart from the main fuse (15 A), there are 5 other fuses on the Power supply board (two each 1A & 1.5A and one 2A). I removed all 5 but same result i.e. failing DB test. So even with no fuse, disconnected amp boards, it still shows short.
 
whilst it is possible its unlikely ..
most likely is outputs followed by rectifier diodes ..
test outputs for short first to try and narrow it down to one channel .
 
measure resistance across the main filter capacitors,

go from the silver grounding straps, to the dual rectifier heat sink type straps that rise above the left (gwr-106) and right (gwr-107) rectifier board assemblies in the little boxes, they are the common DC point, the AC comes in on the individual diode leads.

The cap hot leads themselves are shrouded by the left and right rectifier board assemblies.

somebody that understands this, please talk him through it.

something that pulls THAT much juice should stick out like a sore thumb.

The rectifiers themselves rarely fail, none have been mentioned in this forum in all the time I have been here, to my knowledge.
 
petehall347 said:
whilst it is possible its unlikely ..
most likely is outputs followed by rectifier diodes ..
test outputs for short first to try and narrow it down to one channel .
Click to expand...

Thanks but I have already disconnected both the amplifier boards and still have the problem. You still think it could be output transistors ?
 
sorry not familiar with that model so i don't know if pulling the boards removes output transistors from the power supply or not ..
do as mark says and measure resistance at the rectifiers ..it should show where the obvious short is then we can work forwards ..
power off and unplugged from now on please ..
 
The amp boards have white Molex plugs on the top and bottom.
Did you pull all the Molex plugs on each amp board?
 
zebulon1 said:
The amp boards have white Molex plugs on the top and bottom.
Did you pull all the Molex plugs on each amp board?
Click to expand...

There are 4 Molex connectors per board. 2 connects output transistors to the amp board and 2 connects power amp board to other boards of the receiver including main DC power supply. I disconnected only 2 connecting the power supply. I did not disconnect the power transistors from the amp board. I guess not required as there is no power supply to the amp board.
 
Wrong.
You have to remove both the regulated and unregulated supplies.
All kind of things go on in that amp board!
All the connectors need to be removed.
Now if the DBT dims you know a output(s) is shorted. Hopefully that's all it is. But that wont be an easy or cheap fix.
 
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petehall347 said:
sorry not familiar with that model so i don't know if pulling the boards removes output transistors from the power supply or not ..
do as mark says and measure resistance at the rectifiers ..it should show where the obvious short is then we can work forwards ..
power off and unplugged from now on please ..
Click to expand...

removing 2 molex connector completely isolates the power amp board including the main transistors.

can you please give little more details on how should I measure the resistance. Attach please find is the picture of the power supply board
 

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zebulon1 said:
Wrong.
You have to remove both the regulated and unregulated supplies.
All kind of things go on in that amp board! a Feed back circuit for one.
All the connectors need to be removed.
Now if the DBT dims you know a output(s) is shorted. Hopefully that's all it is. But that wont be an easy fix.
Click to expand...

OK thanks. I'll check later tonight and report....
 
Leokarma said:
removing 2 molex connector completely isolates the power amp board including the main transistors.

can you please give little more details on how should I measure the resistance. Attach please find is the picture of the power supply board
Click to expand...

each side of your pic there are 2 bars holding the rectifier diodes .. these bars are where the main power rails for the output transistors derive from . one is negative rail the other positive .. there are 2 for each channel "left and right " measure from here to ground with power off . one will likely show an obvious short .
 
to the grounding BAR, black dmm lead/probe. down in and right next to each rectifier board in those little open faced boxes., connected DIRECTLY to the big capacitor's terminals.

And the power transistors are STILL connected to the main caps when the amplifier board is completely unplugged (all 4 connectors)

I don't have room to post a marked up picture, if someone (pete, leo) wants to pm me an email address I send them a marked up picture. They can post it if they wish.
 
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