wellswang
Member
Hi,
I have a TRS-80 CC2 which model no is 26-3127. I checked the manual and found that it may simlar to 26-3027.
Please check the mainboard:
When I power on, the display screen twisted at first:
I found +5v of all chips is below 4v, about 3.5v. The AC input is not AC15v, it measured only AC10v.
So i disconnected AC transformer and soldered a +5v DC input on C5 positive.
The display screen not twisted again, but it shows some vertical bars and question marks.
I thought RAM chips may corrupt, so I desoldered all RAM chips and replaced with new 4164s.
But problem still exists. All 8 RAM chips passed tested on another system.
Then I replaced following chips:
MC6809: tested on another CC2, and it's OK. replaced with another MC6809, problem still exists
74LS783: tested on another CC2, it's ok. replaced with 74LS785, problem still exists
74LS138: replaced with another 74LS138, problem still exists
74LS244: replaced with another 74LS244, problem still exists
74LS02: replaced with another 74LS02, problem still exists
MC6847: tested on another CC2, it's ok. replaced with another MC6847, problem still exists
MC6822: tested on another CC2, it's ok. replaced with another MC6822, problem still exists
MC6821: replaced with MOS6520, problem still exists
NE555: replaced with new NE555, problem still exists
I replaced almost all chips but problem still exists.
I also tried to use 27C64 to replace the ROM chip and built an DIP28-24 adaptor. It still failed.
28-24 adaptor connection (red pin number were connected each other):
Please help me to find out the problem. Thanks!
BR,
Wells.
I have a TRS-80 CC2 which model no is 26-3127. I checked the manual and found that it may simlar to 26-3027.
Please check the mainboard:
When I power on, the display screen twisted at first:
I found +5v of all chips is below 4v, about 3.5v. The AC input is not AC15v, it measured only AC10v.
So i disconnected AC transformer and soldered a +5v DC input on C5 positive.
The display screen not twisted again, but it shows some vertical bars and question marks.
I thought RAM chips may corrupt, so I desoldered all RAM chips and replaced with new 4164s.
But problem still exists. All 8 RAM chips passed tested on another system.
Then I replaced following chips:
MC6809: tested on another CC2, and it's OK. replaced with another MC6809, problem still exists
74LS783: tested on another CC2, it's ok. replaced with 74LS785, problem still exists
74LS138: replaced with another 74LS138, problem still exists
74LS244: replaced with another 74LS244, problem still exists
74LS02: replaced with another 74LS02, problem still exists
MC6847: tested on another CC2, it's ok. replaced with another MC6847, problem still exists
MC6822: tested on another CC2, it's ok. replaced with another MC6822, problem still exists
MC6821: replaced with MOS6520, problem still exists
NE555: replaced with new NE555, problem still exists
I replaced almost all chips but problem still exists.
I also tried to use 27C64 to replace the ROM chip and built an DIP28-24 adaptor. It still failed.
28-24 adaptor connection (red pin number were connected each other):
Please help me to find out the problem. Thanks!
BR,
Wells.