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New guy vs CR-840

Kirk V9

Kirk V9

New Member
Just joined up a few days ago and I have a project that I want to try to get going. From my previous career in the AF I have some electronics training that was quite a while ago but is slowly coming back to me.

Last week I picked up a rough CR-840 off of the local classifieds. It’s not pretty but it gives me something to work on. The unit is complete although a little dirty, it definitely been sitting for quite a while unused most likely because it doesn’t work.

I’ve downloaded some really bad copies of the owners manual, parts list and service manual online.

When I got it home I plugged it in to see what there was to see or not see. After cleaning the power switch so that would work properly I pressed it and the red power light comes on. It starts dim and gradually gets to its maximum brightness, on shutdown it is the opposite. Starts bright and slowly dims.

The speaker relay does not click or activate, non of the display lights come on, and there is no movement in the signal or tuning meters.

All the fuses have been checked and are serviceable.

There is definitely minor bulging on some of the electrolytic caps.

I have tested the power supply voltages and got the following readings:

Blue & Yellow - 27.5 VAC
Blue & Orange - 51.7 VAC
Yellow & Orange - 79.9 VAC

From another thread I read that TR801 regulates the 41 V, this is the one with the square tube heatsink near the big caps. TR805 (same type of transistor near the 9 pins) regulates a 26V B supply to the tuner board. If either of those transistors are toast the protection circuit will not work.

TR801: -4.5 VDC
69.6 VDC
0.1 VDC

TR805: 36.4 VDC
36.4 VDC
35.9 VDC

Also from another thread The three wires going to the tuner board should be; white = neg 41V, red = pos 41V, and orange = pos 26V. If all three voltages are correct then the transistors are OK.

My readings at these points:
White: - 46.5 VDC
Red: - 4.5 VDC
Orange: + 35.7 VDC

So after saying all of this I am not certain but it seems to me (and my limited knowledge) that the voltages at TR801 and 805 are incorrect.

So my questions are for anyone who can help:

1. Do you see any problems with my testing so far?
2. What would be my next step?
3. Where can I get some decent schematics, block diagram and service manual (paper or PDF) that will allow me to zoom in and read the small print?

Thank you

Kirk
 
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If the power LED takes time to get bright there might still be a power switch problem. Do you hear a crackling from the switch as it powers up? The switch could be arcing. That's probably not causing the other issues but should be addressed. You could put a short across the switch to hotwire it on for now.

It would help to know which pin of the transistors is which. (Emitter, collector, base). If it is the TO-220 transistor, which I think, the pinout is BCE left to right if you are facing the lettering. You can google the number (plus 2S at the front, so it looks like 2SD313 or something like that.) And the datasheet will confirm pinout. The 69V pin on TR801 would be the collector I think. Looks like you have a power supply issue but hard to say which part it is from here.

Hopefully the output modules are okay.

It would help to build a dim bulb tester to make sure you don't cause further damage as you work on it. Lots of posts on this forum for how to build one. Basically a light bulb in series with the mains supply to limit current.
 
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Raccoon1400 said:
If the power LED takes time to get bright there might still be a power switch problem. Do you hear a crackling from the switch as it powers up? The switch could be arcing. That's probably not causing the other issues but should be addressed. You could put a short across the switch to hotwire it on for now.

It would help to know which pin of the transistors is which. (Emitter, collector, base). If it is the TO-220 transistor, which I think, the pinout is BCE left to right if you are facing the lettering. You can google the number (plus 2S at the front, so it looks like 2SD313 or something like that.) And the datasheet will confirm pinout. The 69V pin on TR801 would be the collector I think. Looks like you have a power supply issue but hard to say which part it is from here.

Hopefully the output modules are okay.

It would help to build a dim bulb tester to make sure you don't cause further damage as you work on it. Lots of posts on this forum for how to build one. Basically a light bulb in series with the mains supply to limit current.
Click to expand...

The power switch is not making any noise. When I first brought the unit home the switch wasn’t latching properly so I gave it a good cleaning and operated the switch a lot before applying power. It SEEMS like it is working correctly.

I will build a dim bulb tester tomorrow and figure out where the voltages are on those transistors.
 
avionic said:
Hifi Engines service manual's schematic is totally wrong.. It shows a discreet amplifier schematic. But the CR-840 has "chip " amplifiers.
Click to expand...
The power supply section is on the same incorrectly illustrated schematic.I'd have to assume that it is incorrect as well.
 
Quick update.

I’ve downloaded an awesome copy of the service manual that I can actually read with my old eyes.

I made myself a dim bulb tester. With a 60W bulb and power applied to the tester, I plugged in the 840 and depressed the power button to the “on” position. The tester bulb started semi bright and then gradually dimmed to the point where it wasn’t visible any longer. If I understand correctly then this proves that there is not a short within the receiver.

I tested TR 801 & 805 again and noted the values as follows:

TR801 Collector: +66.5 VDC
Base: - 4.5 VDC
Emitter: - 3.6 VDC

TR805 Collector: 34.3 VDC
Base: 34.3 VDC
Emitter: 33.8 VDC

I had to remove 805 to figure this out. It’s soldered back in now.

Kirk
 

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Kirk V9 said:
Quick update.

I’ve downloaded an awesome copy of the service manual that I can actually read with my old eyes.

I made myself a dim bulb tester. With a 60W bulb and power applied to the tester, I plugged in the 840 and depressed the power button to the “on” position. The tester bulb started semi bright and then gradually dimmed to the point where it wasn’t visible any longer. If I understand correctly then this proves that there is not a short within the receiver.

I tested TR 801 & 805 again and noted the values as follows:

TR801 Collector: +66.5 VDC
Base: - 4.5 VDC
Emitter: - 3.6 VDC

TR805 Collector: 34.3 VDC
Base: 34.3 VDC
Emitter: 33.8 VDC

I had to remove 805 to figure this out. It’s soldered back in now.

Kirk
Click to expand...
Kirk
Have a good look at TR803 it may be shorted C-E. Also have a look at C803,5 and 9.
 
Can I check that TR in circuit or will it need to be removed?

none of the caps look HORRIBLE, but some of them are bulging a little on top and one has some white crud on it.

I’m planning I’m doing a full recap if I can get this thing powered up.
 
Kirk V9 said:
Can I check that TR in circuit or will it need to be removed?
Click to expand...
To check just the C-E leads no. Just check them for a shorted condition with no power applied. To properly check all junctions yes it will need to be removed.

C1815 is ECB..
 
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