EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: cprobertson1 on March 07, 2018, 11:54:45 am
-
Good Morning folks!
Link to Manual (http://radionerds.com/images/8/88/TM_11-6625-3200-14.PDF)
I've just done the first wave of repairs on my Racal-Dana 5002 wideband level meter - the mains filter blew (https://www.eevblog.com/forum/chat/iec-mains-filter-failures/msg1443991/#msg1443991) and I've since replaced it.
The unit now has power-up issues, which I've partially resolved, I'm getting an "Er 01" error showing on screen:
Er 01 displayed.
Step 1. Press RECALL key, then number 0 key twice. Enter 97 . 1 using numeric
keys. Press SHIFT then SF keys. Verify display shows <50?V and Ur.
• If incorrect, proceed with step 3.
Step 2. Using Digital Voltmeter, verify BT1 voltage > 2.5Vdc (fig. FO-2, sheet 2).
• If correct, Voltmeter is operational.
• If incorrect, replace BT1 (para 5-36).
Step 3. Troubleshoot around RAM A1U20 and U21 using (fig. FO-2, sheet 4).
• Replace faulty component.
Firstly, the battery is missing (the previous owner must have removed it) - so I've bodged in some wires so I can hook it up to the bench meter for now (I'll add in a lithium button cell holder if I have a spare kicking around somewhere)
However, even when supply the specified 3V, the error remains - so proceeding forward to step 3 - "troubleshoot the ram using FO-2-pg4"!
So - the question is this! How do I test these CY7C148 (http://media.digikey.com/PDF/Data%20Sheets/Cypress%20PDFs/CY7C148.pdf) RAM ICs to confirm they are working? :-DMM?
My first instincts are to:
- Check the voltage rails
- Look for data (in and out)(poke with oscilloscope)
- Check CS/WE pins
- Dig out the logic probes
- But having said that, I've never tested a RAM IC before... RAM assemblies, sure, just use memtest.exe - but never the ICs themselves!
Stuff I've done so far (only had an hour last night before I decided to go to bed! I'll have something like six hours to look at it tonight though ;))
- Replaced mains filter
- Hooked battery to bench PSU (unit reliably powers up, but still gives error code 01
- Confirmed voltage rails on board (but not at the RAM ICs
-
Urgh that was a nuisance.
Ended up digging out the logic analyser.
The data entering the IC was fine, but readback was corrupted - so it either wasn't writing or reading properly - well I suppose it could actually be both.
Whatever the problem was, I've replaced it with a modern equivalent and we're up and running!
It's even been in spec for the few measurements I've made with it so far; pretty good for a 30-year old bit of free kit!