CA 800 recovery

B

bubba_pa

New Member
brand new to board, and have to say some great info and minds. Got brave enough to disassemble and clean speaker selector switches on my originally owned B-2, and replace protection relays. Now I don't have to get up every 5 mins to tap the switch. Too new to dig into the B-2 further at this time, but want to try to resurrect my CA-800 for learning, so some help needed.

Last played 3 years ago, but would only play (with distortion) in class A. Even that is not working now. Yes, over the years I did switch between normal and A with amp on. Didn't know any better.

Visual inspection, 6300 uF, 50 v caps bulging. I plan to replace these with nichicon LKG1H682MKNS if they will fit (taller than stock). If there is another cap that would be better, can you name it? I will also replace micro switches for A/AB selection and clean/ rework all other switches/pots. Before I sink much money into this, is this a reasonable place to start and then replace/restore from there? All fuses good and protection relay clicks (will also replace at some point). What preliminary readings should I get before I begin work. I've downloaded the manual and have reasonable technical skills, but no technical knowledge, but want to learn.

I would like to use this as a starter project before working on the B-2. Any and all help appreciated. And yes, I did just plug it in to see, I know I'm not supposed to do that. I also have a DBT for the B-2 (kidding).

Thank you, Paul
 
Fantastic that you want to learn, but take it slowly, the CA-800 is a testing refurb. A fellow AKer suggested desoldering the 3(or so) wires
on the filter board that way the tone, filter and volume boards can be removed together, makes life easier.

The main filters should be upgraded to 63V at least, the rails run at about 51.xVolts, little close for comfort. I would also suggest upgrading
to 10000uf. I've done 2, used 13600uf.

A full upgrade will include the following,
- clean all switches pots especially speaker selector and coupler switch
- check for dry solder joints as part of the recap
- check all fusible resistors
- replace known problematic transistor (2SC458) on heat sink of power amps with KSC1845
- replace speaker relay
- replace class A micro switch
- Nichicon PW and EP caps on relay board
- Replace polar tantalums with low noise Nichicon KL, some people use MKS
- Replace the 4 trimmers on the power amp boards with multiturn types (3296P)
- ...

The CA-800 is a nice amp, you will learn a lot...
 
mbz said:
Fantastic that you want to learn, but take it slowly, the CA-800 is a testing refurb. A fellow AKer suggested desoldering the 3(or so) wires
on the filter board that way the tone, filter and volume boards can be removed together, makes life easier.

The main filters should be upgraded to 63V at least, the rails run at about 51.xVolts, little close for comfort. I would also suggest upgrading
to 10000uf. I've done 2, used 13600uf.

A full upgrade will include the following,
- clean all switches pots especially speaker selector and coupler switch
- check for dry solder joints as part of the recap
- check all fusible resistors
- replace known problematic transistor (2SC458) on heat sink of power amps with KSC1845
- replace speaker relay
- replace class A micro switch
- Nichicon PW and EP caps on relay board
- Replace polar tantalums with low noise Nichicon KL, some people use MKS
- Replace the 4 trimmers on the power amp boards with multiturn types (3296P)
- ...

The CA-800 is a nice amp, you will learn a lot...
Click to expand...
Thanks for posts. I have been trying to pour through the info and have seen
 
A lot of suggestions. Trying to sort out a good starting point, so do really appreciate you input. I've recently been able to dig out and set up all my old stuff - B2, Threshold SL 10, Rega 3 with Magnapan tone arm and AQ cart. Even out of spec,they still sound great. Haven't played vinyl for years, forgot what true dynamic range of good recordings sounds like compared to CDs.

I'll look up some numbers for the caps. Can I run them by folks here for approval/alternate suggestions? Starting small and working my way up. Way, long way to go to get to even what some folks here have forgotten, but I'm willing to try.
 
bubba_pa said:
Trying to sort out a good starting point
Click to expand...
Down load the service manual from hifiengine, safe, no spam. The SM is poor quality so also dow load SM for CA-1000, very similiar.
Easy starting point would be relay board underneath. Think there are 3 2SC458's there that should be replaced with KSC1845's.
Alternatively start on the power amps, Nichicon ES and KZ or elna Silmic II's. Clean, reapply thermal paste on outputs. These boards will
build up your confidence...
 
Thanks, have manual for 800, will get 1000.

Spent some time looking it over and the one of the micro switches is definitely fried. No "clicky". Poured through list of caps and transistors for replacements, relay and micro switches.

Found a 3296 multi turn pot http://www.newark.com/bourns/3296y-1-472lf/trimmer-pot-4k7-25turn-th/dp/06X8943. Now my question is, do I need to "center" the pot before wiring it in? Does that question make sense? Want to make sure enough upside and downside regulation to adjust.

Now, wait for parts and time to get them in.
 
For Bias (idle current) trimmers. I preset for zero mv ( usually fully ccw). For DC balance (DC offset) centered..
 
Sometimes the parts list or the schematic or whats actually installed in the unit . Do not agree with each other. Always go with whats installed. Unless your absolutely sure someone else has installed and incorrect part.
 
Finally had some time to work on this. Love the learning curve. the 40 X 80 Nichicon caps for the mains of course did not fit. Went with some 35 mm dia Nichicon 6800 uF, 63 v's. Replaced relay and caps on power board (except the non-polarized). replaced the 2 micro switches on the A/AB selector. Deoxed all other switches/selectors and disassembled and cleaned coupler switch. Checked output transistors (not shorted) and remounted (mica and silicon oxide). Replaced 2SC458' with KSC1845's on Main amp boards. New trim pots on MC. Looked for cold joints, being new, certainly may have missed, but did best I could with decent Weller iron.

On DBT, light comes on strong, dims and then settles down (not dim, can see element, not bright). Protection relay does not activate and no power light. Also low voltage at switched and un-switched outlets on back (44 VAC).

I know that the fusible resistors on MC are not at spec and have ordered new metal films to replace, but not sure that this is the total problem. Also, after disconnect from DBT and switched off, when I checked the single diode on the power board, the protection relay would release, so believe the PR to be good.

Readings so far:

SP out to E, on L -9.38 V, R 0 V. Half way there.
E to -50/+50: L -16.83/15.36 R -16.76/15.33
E to -B/+B L -10.51/10.5 R -10.54/10.55
E to A L 9.78 R -1.26
E to B L 11.02 R 2.43
E to C L 11.01 R 2.43
E to S L 11.24 R 3.03

I know that voltage at SP out to E should be 0, problem appears to be on Left side. Adjusting VR601 doesn't do anything. Haven't tried to make any more adjustment as it won't come out of protection mode.

All measurements no speaker load, coupler "off", DBT on, but still in protection mode.

Being new to all of this, what is my next step? No smoke and flames yet, so still feeling optimistic. Pre-amp section did work before I started this project. Neither A/AB power amp side did. Class A was last to go.

I also don't have internet access at home where I work on this amp and end up going back and forth to research, then repair, so takes so much more time. Thanks for any and all help. I'd like to hear the amp come to life again.
 
bubba_pa said:
SP out to E, on L -9.38 V, R 0 V. Half way there.
E to -50/+50: L -16.83/15.36 R -16.76/15.33
E to -B/+B L -10.51/10.5 R -10.54/10.55
E to A L 9.78 R -1.26
E to B L 11.02 R 2.43
E to C L 11.01 R 2.43
E to S L 11.24 R 3.03
Click to expand...
Are these readings with the dim bulb ? Nevermind..helps if you read the entire post..:rolleyes:
 
Last edited:
Also check your output transistors case (collector) voltages. Thats your +/- 50 PS.
 
That would be the resistor case(collector) to E, correct? Previously checked Base to case with red VM lead to case and black VM to emitter and all showed conductivity.
 
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